Ecology and Behavior

of the Giant Wood Spider

Nephila maculata (Fabricius)

in New Guinea

MICHAEL H. ROBINSON

and

BARBARA ROBINSON

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 149
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SMITHSONIA N CONTRIBUTION S T O ZOOLOG Y • NUMBE R 14 9

jicology and Behavior

of the Giant Wood Spider

Nephila maculata (Fabricius)

in New Guinea

Michael H. Robinson

and Barbara Robinson

SMITHSONIAN INSTITUTION PRESS

City of Washington

1973
ABSTRACT

Robinson, Michael H., and Barbara Robinson. Ecology and Behavior of the

Giant Wood Spider Nephila maculata (Fabricius) in New Guinea. Smithsonian

Contributions to Zoology, number 149, 76 pages, 30 figures, 11 tables, 1973.-—

Investigations of the seasonal, reproductive, and population ecology of Nephila

maculata are reported in detail. In an investigation of feeding ecology over a

one-year period, the discarded remains of the prey caught by a sample population

of ten adult female spiders were collected daily. These remains were identified

(where possible) and the accumulated weekly discards from each spider were

dried and weighed. Data from this study are analyzed, tabulated, and compared

with the catches from insect traps located in the study area. The study included

an investigation of web structure, frequency of web renewal, and the number of

kleptoparasites associated with Nephila maculata.

Studies of behavior included courtship, mating, predatory behavior, and

responses to predators, sunlight, and rainfall. Courtship behavior included a

complex pattern of silk deposition by the male on the female, here reported for

the first time for the Araneida. The predatory behavior of N. maculaia is analyzed

in terms of behavior units and behavior sequences and is compared with that of

other Nephila species, related species, and that of other araneids studied by the

authors.

The phenological aspects of the study are stressed and discussed.

OFFICIAL PUBLICATION DATE is handstamged jji a limited .number of initial copies and is recorded

in the Institution's annual report, Sm^tnsonian Year. SI PRESS NUMBER 4779. SERIES COVER

DESICN: The coral Montastrea cavemosa (Linnaeus).

Library of Congress Cataloging in Publication Data

Robinson, Michael H.

Ecology and behavior of the giant wood spider Nephila maculata (Fabricius) in New Guinea.

(Smithsonian contributions to zoology, no. 149)

Bibliography: p.

1. Nephila maculata—Behavior. 2. Spiders—New Guinea. I. Robinson, Barbara, 1931—

joint author. II. Title. III. Series: Smithsonian Institution. Smithsonian contributions to

zoology, no. 149.

QL1.S54 no. 149 [QL458.A65] 591'.08s [595'.44] 75-1905

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C., 20402 - Price $1.45 (paper cover)
Contents

Page

Introduction 1

The Species 2

Techniques of Study 3

The Study Area 7

Natural History and Ecology 7

Web Studies 7

Web Location 7

Web Structure 8

Web Renewal 10

Web Strength 12

Reproduction 12

Males on Webs of Females 12

Egg-laying . 13

Hatchling Behavior and Dispersion 14

Phenology of Population Increments 15

Prey and Prey Captures 17

Taxonomic Range . 17

Numbers in Taxa 17

Temporal Distribution . 19

Weights of Prey Remnants 21

Comparison with Argiopc argentata 23

Comparison with Insect-Trap Catches 24

Rejections of Trapped Insects 27

Kleptoparasites 29

Numbers and Nature 29

Activities 30

Colonization of Host Webs 32

General Considerations 32

Energetics 33

Phenology 33

Behavior . 34

Terminology 34

Sexual Behavior 34

Finding the Female 34

Courtship 35

Copulation 41

Discussion 41

Predatory Behavior 44

Behavior Units of Nephila maculata 44

Behavior Units of Other Species 52

Behavior Sequences 54

Comparison with Argiope aemula . 59

Comparison with Nephila clavipcs 60

iii
Page

Categorization of Araneids by Predatory Behavior 62

Behavior of Prey in the Web . . 63

Responses to Environmental Factors 64

Defensive and Escape Behavior . 66

Discussion 67

Phenology .. 67

Behavior 69

Literature Cited 70

Appendix 1: Activities of Male Nephila maculata during

Courtship Silk-deposition 73

Appendix 2: Verbatim Notes on Selected Sequences Given

to Large Acridiids 75
Ecology and Behavior

of the Giant Wood Spider

Nephila maculata (Fabricius)

in New Guinea

Michael H. Robinson

and Barbara Robinson

Introduction

Araneid spiders belonging to the genus Nephila

form a conspicuous element of the invertebrate

faunas of both the Old and New World tropics.

In addition, they extend into north and south temperate regions. The adult females of most species

are large and build strong webs of golden silk that

are often of considerable size. McKeown (1963)

cites examples of Nephila species catching and consuming small birds and also mentions that the

natives of the South Pacific use the webs for catching fish. An interesting account of the use of

Nephila silk for fishing appears in a work of fiction

by Olaf Ruhen, a New Zealander with wide experience of the Pacific region. He states (1969:64)

that the web is matted into a wad the size of a

human thumb and flown over the surface of the

sea suspended from a kite. There it is seized by

garfish which are unable to disentangle their teeth

from the silk and are caught. Surprisingly there

have been few studies of the biology of Nephila

species and attention has largely centered on the

taxonomy and zoogeography of this group. Fischer

(1910a, b, c), Hingston (1922a, b, c; 1923), and

Thakur and Tembe (1956) have published short

Michael H. Robinson and Barbara Robinson, Smithsonian

Tropical Research Institute, Post Office Box 2072, Balboa,

Canal Zone, Panama.

accounts of the natural history of Nephila maculata

(Fabricius) in India. Bonnet (1929), Coleman

(1948), Gerhardt (1930), Jager (1960), and McKeown (1963) have written on various aspects of

the behavior or ecology of other Nephila species.

Peters (1954, 1955) studied the web construction of

Nephila clavipes (L.).

Studies of the predatory behavior of Nephila

clavipes in Panama (Robinson and Mirick, 1971)

led to the conclusion that this species was primitive

(Robinson, Mirick, and Turner, 1969). At this

stage we thought that a more comprehensive study

of a Nephila species would be worthwhile and

rewarding. We were able to make some observations on Nephila and related Nephilengys species

in West Africa during February and March 1970,

and further observations on Nephila and Nephilengys in Madagascar and on Nephila and Herennia

in India (March/April 1970). In New Guinea we

found that Nephila maculata was abundant in the

Wau valley (Morobe District) where we were to

spend one year at the Wau Ecology Institute. The

spiders living in the arboretum of this institute

were protected from disturbance and we decided to

make a long-term field and laboratory study of this

species.

This paper is based on our studies in New

Guinea but also includes comparative data from
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

the observations carried out in West Africa, Madagascar, and India, and unpublished data from the

study carried out by Robinson and Mirick in Panama. The New Guinea studies were basically

ecological and behavioral. Ecological studies in

eluded observations on web structure and habitat,

sampling of potential and actual prey, phenological

studies of reproduction and predation, investigation

of population numbers of kleptoparasites, and

recording population fluctuations of adult and immature Nephila. The behavioral studies were mainly concentrated on predatory behavior but also

included studies of mating behavior and responses

to sunlight and rainfall. Some effects of behavior

are dealt with in the ecological section of this

paper because the underlying behavior patterns

were not directly studied. This was the case with

respect to prey-rejection, web-renewal and egglaying. Some studies that are referred to in this

paper, e.g., those on web adhesiveness and population fluctuations in Wau araneids, were carried

out in conjunction with our colleague Dr. Y. D.

Lubin and are to be published separately. The

study of five species of Argiope that we carried out

in New Guinea is referred to in the comparative

section on predatory behavior, but it is to be published in detail elsewhere.

ACKNOWLEDGMENTS.—We thank Dr. Y. D. Lubin

for her assistance during this study. She provided

both ideas and practical help. We are extremely

grateful to the staffs of the following institutions

who helped our work in Africa and India: Department of Zoology, University of Ghana, Legon;

O.R.S.T.O.M. and the Institute de Recherche

Tropicale in Ivory Coast; O.R.S.T.O.M. in Madagascar; Bombay Natural History Society; University of Delhi; Hindu University of Varanasi;

Forestry Department of Assam; and, particularly,

Dr. T. N. Ananthakrishnan in Madras.

In New Guinea we received much help from the

staff of the Forestry School at Bulolo, The Lae

Botanic Gardens, and the entomologists of the

Division of Entomology laboratories at Bulolo. Our

native helpers, Rennie, Lik-lik Boy, and Polino

were superb naturalists and cheerful assistants

throughout the study.

Our colleagues at the Smithsonian Tropical Research Institute, have, as always, contributed much

to the development of the ideas presented in this

paper. In particular we are grateful to Dr. A. S.

Rand and Dr. H. Wolda for advice and help with

the analysis of data.

THE SPECIES

Fr. Chrysanthus identified the Wau material as

Nephila maculata. The species has reportedly a

wide distribution in the Old World tropics and

subtropics (Roewer, 1942; Bonnet, 1958). Roewer

(1942:929) gives the distribution as "Ceylon, Indien

bis China u. Australien," while Bonnet (1958:

3077) adds "Afrique occidentale et Afrique australe" and "PMexique." The records of the species

from New Guinea have been detailed by Chrysanthus (1959, 1960, 1971). The species occurs in all

parts of the Wau valley where trees or bushes persist

and we have recorded its presence to a height of

approximately 2000 meters on the slopes of Mount

Kaindi. Densities are often high in coffee plantations, where the species builds its webs in the

flight paths of insects between the rows of plants.

Some details of the appearance of adult males

and females are evident from the photographs illustrating this paper (Figures 17, 18, 19). The adult

female varies in size from just below 40 mm in

body length to over 50 mm; most of this variation

is due to variations in the length of the opisthosoma. Legs i are the longest, legs iv are usually

longer than legs n and legs m are the shortest at

around half the length of legs i. See Table 1 for

specimen measurements, note that there is often

asymmetry in leg lengths. We have records of the

weights of adult females ranging from 2-4.25 grams

and think that the variations in adult weight probably extend above and below this range (taken

from a sample of 10). The adult female is dull and

dark in coloration contrasting markedly with some

other common Nephila species in this respect.

Yaginuma (1969, pi. 29) gives a color illustration

of the Japanese form. The Wau specimens differ

from this in that the opisthosoma is completely

unmarked dorsally. The Japanese form evidently

has pale yellow lines and spots on this region.

Dorsal markings of the opisthosoma are present on

immatures at Wau. They are not present on the

penultimate instar. Hingston's (1922a) description

of Nephila maculata in India refers to striking

coloration of the dorsal surface of the abdomen.
NUMBER 149

TABLE 1.—Sizes of adult female Nephila maculata

(- = leg missing.)

Spider

1

2

3

4

5

6

7

8

9

10

Average

Wet Opisthoweight Length Prosoma soma

(gm) (mm) (mm) (mm)

Leg lengths (mm)

II III IV

R R

4.25

2.725

2.055

4.134

3.575

3.387

3.80

2.93

350

3.75

3.38

41

40

37

40

48

46

47

40

44

50

43.3

11

12

10

11

12

13

12

10

11

13

11.5

30

28

27

29

36

33

35

30

33

37

31.8

82

85

83

84

80

81

79

85

86

82.78

80

86

81

85

83

82

82

82

87

84

83.2

68

72

67

70

67

71

70

67

71

68

69.1

66

71

68

69

68

69

58

72

70

67.9

41

40

42

40

41

39

41

38

40

41

40.3

39

40

39

37

40

38

42

39

40

39.3

69

71

68

70

68

69

70

69

69

68

74

69

56

69

71

74

71

68.9

Juveniles up to at least half the adult size (Figure

1) possess the dense hairy "gaiters" on the distal

portions of the tibiae of legs i, n, and iv that are

FIGURE 1.—Juvenile Nephila maculata showing "gaiters" on

legs (arrowed) that are lost in later stages. Length ca 25 mm.

characteristic of all stages of Nephila clavipes and

several other Nephila species. The females of later

stages lose the gaiters as Thakur and Tembe (1956)

have also noted. These authors include a figure of

an adult female showing dorsal lineation and spotting on the opisthosoma (1956, fig. 1). The opisthosoma of Wau adults is a dark slatey color (almost

black) with an overlying "bloom," or "patina," of

gold; the latter appears to wear off with time. We

found a number of adult females in the Wau area,

which had conspicuous pale yellowish brown legs

in marked contrast to the black legs of the "normal" form. One of these is illustrated in Figure 2,

and a specimen is deposited with Fr. Chrysanthus.

This form is a distinct one, and not merely a product of slow deposition of the appropriate pigmentation.

Adult males are very small, ca. 4-6 mm in body

length and transluscent red to reddish orange in

coloration, often with black markings on the tarsi.

TECHNIQUES OF STUDY

During the period May 1970 to May 1971 we

carried out daily observations on a sample population of adult female spiders present in the study

area (described later); and from June 1970-April

1971 we carried out the sampling of flying insects

in the same area. During daily observations we

noted the state of the web and its position; the

presence or absence of males and kleptoparasites,

the presence or absence of prey, and evidence of

egg-laying as reflected in sudden reductions in the

grossness of the female opisthosoma and/or the
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FKU U 2.—Revene color form of adult Nephila maculata in typical predatory position at hub.

presence of nearby egg-sacs. This recording involved

visiting ten marked adult spiders daily. Prey traps

were placed under the webs of these spiders and

discarded or rejected prey were collected daily for

further examination and analysis. In addition to

this daily routine we carried out (with Dr. Y. D.

Lubin) weekly counts of all the visible araneids in

three 100x2 meter transects, one of which bordered

the study area. These counts included counts of

adult and immature Nephila maculata. We also

censused the kleptoparasites present in Nephila

webs outside the study area but within a 500 meter

range of its center.

Behavioral observations were carried out on adult

spiders living in the study area but not forming

part of our sample population. The investigations

on predatory behavior utilized similar techniques

to those employed by the senior author and coworkers in earlier studies and will not be described

in detail here. New techniques used for the first

time in this study are described in the appropriate

section of the main text. Extensive use was made

of filming and film analysis, particularly in the

study of mating behavior. We used Super 8 inm

movie film for this purpose. This allowed us to use

considerably more portable equipment than was
NUMBER 149

possible in previous studies where we used 16 mm

film. For filming behavior sequences we used a

Canon 518 camera equipped with the manufacturer's close-up lens. This enabled us to fill the frame

with a portion of the body of the adult Nephila

female, and, incidentally to use the viewing system

of the camera to watch events that were not clearly

visible to the unaided eye. Using zoom optics for

this purpose provides an admirable technique for

studying the behavior of small animals from a convenient distance (Robinson and Robinson, 1972a).

All the black and white photographs were taken

with a 6 cm square single-lens reflex camera equipped with close-up attachments. The photography of

spider's webs is difficult (see Langer and Eberhard,

1969) but can be facilitated by spraying the web

with matt-white aerosol paint and then interposing

a black background between the web and surrounding vegetation. All the accompanying photographs

of web structure were taken by utilizing this technique.

The rainfall data that we include in the phenological analyses are derived from the records of the

Wau Ecology Institute and New Guinea Gold fie Ids

Company.

PREY TRAPS.—Our observations on the prey of

Argiope argentata (Fabricius) in Panama were

carried out by visiting ten webs at two-hourly intervals throughout the day and recording details of

the prey present in the web. This method is extremely tedious and time-consuming and does not

permit a determination of weights of prey except

by extrapolation from weighed samples. Spiders

are suctorial feeders and discard "trash packages"

of prey remains after feeding. We decided to collect these packages for weighing and identification.

To do this we placed meter square pieces of fine

nylon netting under the webs of the ten "sample"

spiders and collected the remains each morning. To

prevent ants from removing prey debris we coated

the prey trap attachment strings (one at each corner) with tanglefoot. The method proved entirely

satisfactory. The traps caught the remains of

quite small prey (as small as 5 mm insects), the

conspicuous remains of large prey, and the dead

bodies of rejected prey items. The latter was a

"bonus" item resulting from the fact that N. macula t a rejects many items of obnoxious prey after

a preliminary bite. (If heavy rain occurred during

the 24-hour interval between emptying the traps, it

may have washed some very small fragments of

prey through the mesh, but we think that this

factor was a very small source of error in our

results.)

The material from each trap was placed in a

separate vial each day, dried in a drying oven, and

the seven samples from each spider were examined

under a binocular dissecting microscope at the end

of each week. This process allowed us to make a

record of prey caught, on each day of the week.

We also obtained a weekly total for the dry weight

of prey remains discarded by each spider. (We

decided that weighing the wet remains would not

give any useful information because of wide variations in water content due to climatic conditions.)

Sorting the material under a binocular microscope

was not easy since the masticatory process results

in the extreme comminution of those insects that

have thin cuticles. It proved possible, however, to

identify most trash bundles to order and often to

lower taxonomic divisions. The jaws and jumping

legs of orthopterans served to identify the fragmented remains of those insects and the color of

the cuticular fragments was a further guide to

separation. Lepidopteran remains were characterized by the presence of wing scales. The elytra of

even the smallest coleopterans survived the comminution of other parts. Compound trash parcels

could often be separated into their multiple constituents by counting elytra, jaws, and other hard

parts, and the number of prey items thereby calculated. Occasional forceps marked the presence

of dermapterans and we were able to sort out some

dipterans and hymenopterans on the basis of their

membranous wings. Catches from the nearby insect

traps were useful in giving an indication of the

potential presence of some groups of flying insects

that were periodically in abundance. These data

helped in the determination of dubious prey remains. Larger insects that were not caught by the

prey traps (e.g., melolonthids and sphingids) were

seen at our Mercury vapor (Mv.) insect light and

very abundant flights were noted for comparison

with the prey trap data.

The spiders were marked with Humbrol modelmakers enamel paint using a color/position code to

identify individuals. The paint peeled off the surface of the opisthosoma after about one month so
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

it was necessary to re-mark the spiders every three

weeks. We usually had twenty marked spiders in

the study area; the ten sample spiders and ten "reserves." The latter were used when one of the

sample spiders died, disappeared or moved into an

inaccessible position. Movement to an inaccessible

position occurred very rarely since we were able to

arrange the prey traps at most web sites (even when

this involved some removal of surrounding vegetation.) The fact that the spider builds its web across

gaps in vegetation, in flight paths, normally ensured that there was a fairly clear space beneath

the web in which to erect the prey trap.

We recovered the dead bodies of some spiders

from the prey traps but lost most of our sample

specimens by "disappearance." Our very skilled and

sharp-eyed New Cuinean assistants usually found

spiders that had merely moved long distances from

the original web sites but many spiders disappeared

without trace at some stage in the prey census. We

discovered at an early stage in the study that very

fat spiders would disappear for one or two days and

then return, much depleted in size, to the same web

location. These had produced egg-masses. As a

consequence of this observation we decided not to

replace missing sample spiders until they had been

absent for three morning censuses. In time we

noticed that egg-laying absences were often preceded

by nonrenewal of the web and a fall off in catches

for the days immediately prior to the absence, and

this factor helped in the interpretation of disappearances. Spider movements largely occurred at

night, and were noted the following morning, when

the trap could be relocated. Thus there was very

little disturbance of the data collection by movements from web site to web site. Individuals remained under observation for several months and

provided data on minimum periods of adult

longevity.

INSECT TRAPS.—To sample the availability of

potential prey we used two techniques. We placed

three window-pane traps at sites in the study area

that were typical of web locations and collected the

insects from these, each morning, over most of the

study period. We also used two sticky traps for a

shorter period (necessitated by the late arrival

of our supplies of tangle-foot); these traps were also

serviced daily.

We chose window-pane traps as a sampling deFIGURE 3.—Window-pane trap in study area.

vice since we considered these to be less conspicuous

to flying insects than the opaque mass of a sticky

trap. They, in fact, trapped insects not caught by

sticky traps but failed to catch some insects known

to be in flight (from our observations of the spider's

prey and Mv. light catches.) These insects, including large beetles and moths, were not caught by

the sticky traps either. We have discussed elsewhere

(Robinson and Robinson, 1970a:356) the problems

involved in sampling the prey available to large

orb-weavers and do not consider that these have

yet been solved.

The window-pane traps were constructed of

pieces of 24-ounce clear sheet grass 24 X 24 inches

in size (about 61 x 61 cm). This was mounted in

a light wooden frame and its lower edge dipped

into a 3 cm tleep trough of water. The water

contained a wetting agent and a small quantity of

phenol. Figure 3 shows a trap in situ. We mounted

the traps on wooden legs with their centers about

1 meter above ground level.
NUMBER 149

The sticky traps were made by smearing both

sides of a meter square of nylon mosquito netting

with tanglefoot (I.C.I. Osticon) and mounting the

net on a light wooden frame. The traps were

erected with their bottom edges about 75 cm above

ground level.

Insects from the window-pane traps were preserved in 70 percent ethanol and those from the

sticky traps were collected in gasoline and transferred to alcohol after the tanglefoot had been

dissolved. The daily catches were examined monthly, sorted taxonomically, and graded into size

ranges.

THE STUDY ARKA

The approximate boundaries of the study area

are shown on Figure 4. The area was originally a

coffee plantation but, over a period of years, has

been converted into an arboretum by the activities

of the Wau Ecology Institute (formerly Bishop

Museum Field Station). Trees from Mount Kaindi

and other areas in the Wau-Bulolo region have

been planted and have reached a considerable

height above the remaining rows of coffee. The

latter is picked periodically but was not pruned

FK;I!RK 4—I'lan of study area (hatched). (Black circles = large

trees, b — bamboo thicket, s^sticky trap, w = window-pane

trap. Stiplcd area is transect 1.)

during our study year. Some of the tree and shrub

species occurring in the area are as follows:

Rubiaceae: Gardenia species, Neoxandia species, Psychotria

species, PaveUa species

Euphorbiaccac: Phyllanthus species, Euphorbia pulcherrima,

Macaranga species

Meliaceae: Disoxylon species, Toona sureni

Moraceae: Ficus calopilina, Ficus dammaropsis

Sapindaceae: Dyclioneura species, Allophyllus species

Elaeocarpaceac: Elaeocarpus sphericus, Elaeocarpus dolichostylus

Anonaccae: Anona muricata

Solanaceae: Datura Candida

Araucariaccae: Araucaria klinkii

Sterculiaccac: Sterculia species

Myrtaccac: Eugenia species

Lauraccac: Litsia species

Melostomaceac: Astronia species

Rhamnaceac: Alphitonia incava

Verbenaceae: Callicarpa longifolia

Some idea of the height of the background vegetation can be gained from Figure 3. The area

supports a diverse fauna including numerous arthropods that are predators of arthropods. Among these

are trap-building spiders of the families Uloboridae,

Amaurobiidae, Pholcidae, Araneidae, Tetragnathidae, Agelinidae, Linyphiidae, and Theridiidae.

Araneids included three species of Gasteracantha,

two of Argiope, two of Leucaxige, one of Cyrtophora, one of Arachnura, several araneus-like nocturnal forms, Herennia ornatissima, Cyclosa

insulana, and the, as yet, unidentified "New Guinea

ladder-web spider" (Robinson and Robinson,

1972b). The theridiids include solitary, colonial,

and kleptoparasitic forms. The trap-building spiders exist alongside a large hunting spider population and some sedentary raptors (dinopids). In

addition there is a diverse assemblage of predatory

insects including mantids and reduviids.

Natural History and Ecology

WEB STUDIES

Web Location

Webs of adult female spiders are almost always

located with the bottom edge (lower foundation

thread) above the herb layer, even when this

attains a height of more than 1 meter. A proportion

of webs may be built with the prey capture area
8 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

partially overlapped by nearby vegetation but in

most cases webs span natural gaps in woody vegetation. Hingston (1922a:643) notes that Indian

N. maculata often builds its web where "it finds a

tunnel in the tangled growth where the insects

pass to and fro." We found webs located in trees

at heights of more than 5 meters above the ground

and even sited on telephone and overhead power

cables. Webs of males and immatures were discovered closer to ground level and sometimes within

the herb layer. Back-to-back, web building, as noted

in the case of N. clavipes (Shear, 1970), was uncommon in the Wau area.

Web Structure

In common with the webs of those other Nephila

species that we have seen, the webs of N. maculata

are markedly assymmetric in that the hub is always

located in the upper third of the web. Peters (1954,

1955) has given details of the structure of the N.

clavipes adult web, which is frequently incomplete

above the hub (see also Kaston and Kaston, 1953).

The web of N. maculata differs in being almost

always complete above the hub, i.e., with the prey

capture area intact in this region. Some sample

dimensions of webs made by adult females (N = 10)

convey the structural aspects of the web of N.

maculata:

Range

0-10

55-90

69-110

Viscid spirals above hub

Viscid spirals below hub

Radii (counted halfway between

hub and periphery)

Compared with webs of adult males (N=5), the

females' webs are appreciably larger (measurements

in cm):

Average

5.7

72.5

86.9

Female Male

Width

Height

Range Average Range Average

62-100 84.1 7.8-11 9.4

79-116 96.2 10.4-13.1 11.7

In our sample of 3237 webs, those with barrier

constructions occurred in 640 instances (19.8% of

total sample), of which 625 had dorsal barriers

only, and 15 had both dorsal and ventral barriers,

but none had only ventral barriers. We note, therefore, that barrier webs occur with maximum frequency below the orb, i.e., dorsal to the spider. The

structural spiral is left in during construction of

the viscid spiral but since four or five viscid elements are not interspersed between successive

elements of the temporary spiral, it does not present the "music-ruled" effect of the N. clavipes web.

The above web dimensions show that the webs are

often more nearly circular than those of N. clavipes

(i.e., with their greatest width not differing greatly

from their greatest height).

As in all the Nephila webs that we know of, the

lower radii are often branched (see Kaston, 1964,

for comments on evolutionary significance). The

hub is entire and surrounded by a spiral strengthening zone. The hub region often appears to be

braced by a thread leading from the hub silk to

some nearby piece of vegetation. The viscid spiral

is characteristically golden in color. Hingston

(1922a:648, 1922b:912,1922c:918) gives details of the

structure and process of construction of the Nephila

maculata web. He notes that the radii are branched

and numerous (more than 100), that the temporary

spiral is left permanently in place and that a barrier web is built above the main sheet. He also

observed a marked asymmetry in the placement of

the hub and quotes an example (1922c:918) where

a web had 130 turns of the viscid spiral below the

hub and only 3 above.

The webs of males were found sporadically in

the study area and we have seen mature males with

a web. They were all small and more like the

normal, almost symmetrical orbs of Araneus diadematus.

The webs of immature females proved to be of

great interest for two reasons. First, a proportion

were found that had linear stabilimenta (Figure 5).

These structures consist of a ribbon of silk placed

above and below the hub and consist of multistrand silk, laid down between adjacent radii in a

zig-zag line. We never saw any stabilimenta in the

webs of mature females. As far as we are aware this

is the first and only record of stabilimentum building by a Nephila species. We saw 14 such structures

in the course of examining hundreds of webs over a

one-year period. Although we never saw the spider

construct a stabilimentum it is obvious that it is

not an accidental structure resulting from some

anomalous aspect of web-building, but is added

alter the completion of the viscid spiral. It is

tempting to regard this aspect of N. maculata's web

building behavior as vestigial. Elsewhere (Robinson
NUMBER 149

FIGURE 5.—Juvenile Nephila maculata with stabilimentum.
10

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

and Robinson, 1970b) we have reviewed the various

theories about the function of stabilimenta and

concluded that in some cases, at least, a camouflage

sensu lato function, is improbable. This would

certainly seem to be the case with the rarely built

stabilimentum of N. maculala. (Nephila species do

apparently construct some camouflage devices; both

N. maculata and N. clavipes deliberately hang plant

material and discarded prey debris in their barrier

webs above the hub. Nephila plumipes (Latreille)

often hangs the corpses of prey in a line above the

hub.)

The second interesting feature of some juvenile

webs is the form of the barrier webs. Note in Figure 6 that the spider is standing on the main orb

and that there is a netlike large barrier web dorsal

to the spider and a smaller, incomplete, similar

barrier web below the main orb. The structure of

these barrier webs, an orb web structure with radii

and a structural spiral, has not been previously

described. The hub of the barrier orb is drawn

away from the functional orb by an attachment line

so that the effect is one of a conical dome above

and below the web proper. This highly organized

pair of structures is replaced at later stages by the

apparently disorganized maze of lines that make

up the barrier web (s) of the mature spider. As in

the case of the stabilimentum we were not fortunate

enough to see such barrier webs actually being

built. It is, however, clear that they are not adventitious structures built by other spiders. The

greater development of the structure dorsal to the

spider supports the suggestion that the barrier web

may protect the spider against its predators, in this

case it would clearly prevent, or delay, attacks by

spider-hunting wasps and parasitic dipterans. (A

number of explanations of the function of barrier

webs are current among arachnologists but few have

been published. Hingston (1922c) suggests that it

prevents the escape of large prey from the main orb.

He reasons that large insects may tear themselves

free of the viscid spiral but that they are then

likely to strike the barrier web and be driven back

into the main orb. This theory accounts for some

features of the structure of barrier webs but not

their preponderance below the orb, i.e., above the

spider's back.)

The plane of the N. maculata orb web seldom

appears to be perpendicular but is usually inclined

to a greater or lesser extent. We did not attempt

to measure angles of inclination but believe that

the majority of webs fell within the range of 5°-30°

deviation from the perpendicular. The spider assumes its predatory position on the undersurface

of the web. The slope must facilitate transportation

of prey on silk (the spider walks on the undersurface with the prey hanging away from the web, in

the lower and larger portion).

Web Renewal

Our morning census revealed that webs are renewed, entirely or in part, with greater frequency

than we anticipated. It was easy to distinguish renewed parts because the edges of the renewed area

are conspicuous. In addition, the new viscid element in the renewed area looks fresh by contrast

with the old element, in which the viscous droplets

are often irregular and patches of adhering detritus

are usually present.

Web renewal data from the daily census of 10

adult female Nephila maculata are as follows:

Days female absent or on scaffold only: 413

Total possible number of web days (3650-413) :3237

A total of 2388 webs were lenewed or repaired during the

3237 days (each web averaging 1.4 days duration)

Number of webs

renewed or repaired

1794

435

105

31

13

5

3

2

Total: 2388

After

24 hours

48 hours

3 days

4 days

5 days

6 days

7 days

9 days

Percentage of webs

renewed or repaired

daily 75.1

every 2 days: 185

every 3 days: 4.3

within 3 days: 97.6

Nephila maculata cuts away areas of web during

heavy rainfall and renews them later, without completely rebuilding the web. The spider cuts

through the radii, close to the hub, on one side of

the orb and an area of web collapses. (This behavior can be induced by spraying a web with water

and may be a means of preventing the collapse of

the entire web under the effect of a heavy load of

water droplets.) When heavy rainfall occurs at the

stage when the spider would be completing a new
NUMBER H<>

FIGURE 6.—Web of juvenile Sephila maculata showing highly organized barrier webs, spider is

visible on main orb (left center) , barrier web below spider (extreme left) is much smaller than

that above spider (center to right, conical).
12 SMITHSONIAN COM RIBUTIONS TO ZOOLOGY

web, by laying down the viscid spiral, this stage

may be deferred until rainfall ceases. Other stages

up to the addition of the viscid spiral appear to be

carried out during rainfall. Viscid spirals added

after long periods of intermittent rainfall are often

untidy and incomplete.

As mentioned above we carried out, in collaboration with Dr. Y. D. Lubin, a number of experiments on variations in web adhesiveness with time.

We used a modification of the technique used by

Eisner, Alsop, and Ettershank (1904) and tested the

adhesiveness of standard sized lengths of N. maculata viscid spiral, at intervals, over a period of

several days. The viscid spiral, when protected from

rain, maintained a high level of adhesiveness for

more than two days after it had been produced

(Robinson, Robinson, and Lubin, in prep.). This

suggests that chemical deterioration of the adhesive

is not the factor necessitating the recorded frequency of web renewal.

Web Strength

Dr. Y. D. Lubin (in litt.) has compared the

strengths of elements from the webs of Ar. maculata

with those of Cyrtophora moluccensis. The results

give no absolute values but show that the Cyrtophora silk is much stronger than the Xcphila silk.

The latter, however, is strong enough to retain insects in excess of 2 grams (large scarabaeoid beetles)

until the spider can subdue them.

REPKOIH'CTION

Males on Webs of Females

Figure 7 shows graphically the number of males

recorded on the ten study webs during the year and

also, for the second half of the study period, the

number of males recorded actually on the body of

the female during the morning census. We have

also plotted the numbers of males recorded on the

weekly census of transect 1 (p. 4) during the

same period. Males are present on the webs of

females throughout the year and the number

increases markedly from week 36 (commencing 20

January 1971) and remains high until the end of

the study period. The peaks in the number of

males seen on the body of the female coincide

with the peaks in the totals of males recorded on a

female's web, during the period of high numbers.

The greatest number of males recorded on transect

FICIRE 7—Weekly distribution of number of males found on webs of females in study area

and number of males seen on females themselves. Histograms show numbers of males censused

in nearby transect.
NUMBER 149 13

1 also occurs during the period from week 36 to 52.

Figure 8 shows the numbers of adult female and

immature Ar. maculata recorded on transect 1, and

it is interesting to note that the large population

of males on the study area occurs during a period

when the number of immature spiders is high on

the nearby transect (Figure 4).

Several males may attend a female at any one

time. Although we did not mark individuals we

have observed conspicuous individuals (naturally

marked by the loss of legs, or distinctive coloration)

to be present on the same web for several clays.

When not actually on the body of the female the

males take up positions on bridge and frame

threads, on elements of the barrier web (s), within

the upper part of the prey capture area, and at the

hul). Males were also observed on the webs of immature females, often when these must have been

at least two or more molts away from maturity.

We have one record of a male mating with a female

shortly after she had ecdysed, at a stage, in fact,

when she was still hanging from her cast exoskeleton.

Egg-laying

PERIODICITY.—During the year of study, the 10

adult female Nephila maculata produced an estimated total of 89 egg-sacs, which on a monthly basis

were counted as follows: May, 4; June, 9; July, 7;

August, 8; September, 9; October, 9; November, 8;

December, 6; January, 7; February, 9; March, 6;

April, 7. These figures are only for cases of what

we regard as certain instances of egg-laying. (We

scored egg-laying when we found a new egg-sac near

to a marked female that had been absent from a

web site for 1 to 2 days or when a female had been

absent for this period and returned considerably

reduced in bulk although no egg-sac was located.

Because of their camouflage, egg sacs are not always

easy to locale.) Spiders that simply disappeared

from our sample may have laid eggs but are not

scored. The estimate must, therefore, be regarded

as conservative.

There was a strong tendency for female spiders

to stop web replacement and repair some days prior

to egg-laying. There was also a tendency for them

to stop feeding in these circumstances. Although

these behaviors are not invariable they are apparent

in the majority of cases as Figure 9 shows.

The old webs occupied by females on the point

of egg-laying were often functional, and the falloff in prey capture was, therefore, in many cases,

50 MALES,PER WEEK. STUDY AREA

FIGURE 8.—Weekly distribution of numbers of adult and immature Sephila maculata on transect

1. Horizontal black bar shows weeks when males were present.
14

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

number of

old wobi

1 2 3 4 5 6 7 8 9 10 11 12 13 14

-spiders obsont

FIGURE 9 Number of prey caught per day and numbers of new webs per day during the two

weeks prior to an egg-laying excursion. Based on data from 50 periods prior to egg-laying.

due to the spider not responding to potential prey

that struck the web at this time.

All the egg-sacs that were found were similar

in structure and golden green in color. Most of the

egg-sacs were constructed under the shelter of

leaves in the upper branches of trees and shrubs

near to the parent female's web site. There, because

of their coloration, they are quite well camouflaged.

DEVELOPMENT PERIOD.—Unfortunately we failed

to obtain data on the development period of eggs

in situ, and eggs that we brought to Europe to study

under laboratory conditions failed to hatch.

Hatchling Behavior and Dispersion

After hatching the spiderlings remain in roughly

spherical aggregations around the egg-sac for up to

nine days. During this time they respond to air

currents by chopping on silk lines, but climb back

into the aggregation after the disturbance has

ceased. Figure 10 shows an aggregation of spiderlings two days after emergence from the egg-sac.

Presence of exuviae in some masses suggests that the

spiders may molt at least once before dispersing.

Lowry (in McKeown, 1963:150-151) described hatching and the subsequent behavior of the hatchlings

in the case of N. plumipes, reporting that the

spiderlings could remain within the egg-sac for a

considerable period before emerging to form a loose

cluster around it. She concludes that emergence

may be conditional on climatic conditions. Thakur

and Tembe (1956:331-332) give data on the shape

of the egg-sacs of N. maculata near Bombay, India,

and speak of the cocoon being placed in "a wellconcealed place." Fischer (1910a) never found the

egg-sacs of this species.

We did not see the process of dispersion but on

a number of occasions noted the overnight disap-
NUMBER 149

FIGURE 10 An aggregation of newly emerged Sephila maculata spiderlings beneath a leaf.

pearance of clusters of spiderlings. Although we

think it probable that they may disperse by ballooning on silk threads, we have not seen aerial dispersals of young in the tropics. Bristowe (1939:187)

has commented that "it is probable that the young

of most species disperse themselves by aerial methods in all countries where a sudden change in

ground temperature occurs in the morning, but

more observations are needed in the tropics before

we can be certain that this means of dispersal is as

important there as in temperate regions." Our

observations at Wau and in Panama suggest that

eggs are hatching at intervals over most of the

year and this fact probably explains the absence

of conspicuous massed migrations of ballooning

spiderlings in these regions. Such migrations are

typically autumnal in the temperate zones (Bristowe, 1939:182-201, for discussion and bibliography). We have certainly recorded the presence of

very young A', maculata, with webs, at distances

of over 50 meters from the nearest known eggcluster. It seems a logical assumption that these

spiderlings arrived at such sites by aerial dispersion.

The group of freshly emerged spiderings of Ar.

maculata shown in Figure 10 has produced a clearly

visible complex maze of threads. Such clumps may

contain more than 1000 spiderlings. Mortality in

the early stages of development must be high.

Phenology of Population Increments

Although we did not monitor the presence of

early stage spiderlings in the study area—an extraordinarily difficult habitat in which to count animals less than 3 mm long—we did census the

adjacent line transect (see page 4 and Figure -1).

Here we recorded the presence of all trap-building

spiders, scoring adult and immature spiders sep-
16 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

arately. It was not possible to measure the spiders

during the census so that records of immatures,

refer to obviously immature spiderlings and include

several instars. All large increments of immatures

were found to be due to early-stage spiderlings.

Figure 8 plots the outbreaks of immature Ar. maculata at this transect. There is a fairly regular increment of spiderlings during most weeks of the

census until week 25 (8 November 1970) when the

number exceeds 15 for the first time. Thereafter

it exceeds 15 until week 50 (2 May 1971). During

the period of this higher density of immatures the

number occurring at the weekly census exceeded

50 on 18 occasions. We think that Kcphila spiderlings are probably emerging over most of the year

in the study area and that the increments in the

marginal transect area support this view. The

larger increments in the wetter months suggest

that conditions may then be favorable for either

hatching, or the survival of the spiderlings, or

both. The occurrence of peak populations of

mature males during this period supports the view

that survival rates may be higher at this time, at

least for spiderlings up to the size of adult males.

This matter is discussed later in an overall consideration of the phenology of the species at Wau. The

data on egg-laying, on the presence of males in

female's webs, and on the occurrence of immatures

at the transect all suggest that reproduction in N.

maculata at Wau, occurs throughout the year. Near

Bombay, India, where Thaktir and Tembe (1956)

carried out their study the climate is much more

markedly seasonal than at Wau. Figure 11 gives

climographs for Bombay, and for Bulolo, New

Guinea, and monthly rainfall data for Wau. Bulolo

is the nearest locality from which we have reliable

temperature data. Near Bombay the N. maculata

population is markedly seasonal. Thakur and

Tembe (1956:330) report that the young appear

at the "end of August and early in September.

Their bodies then measure 1 cm." These are obviously not newly emerged spiderlings which are

smaller than 3 mm in length. Thakur and Tembe

(1956:331) also state that the females become

gravid "during Oc tober and November" after which

eggs are laid. The spiders become very rare by the

end of December, almost absent in January and

"no specimens at all were observed near Bombay

during other months of the year" (Thakur and

Tembe, 1956:330).

Allowing an extra month for the stages occurring

prior to the 1 cm young seen in August, it would

appear from this report that the spider is present

for, at the maximum, seven months of the year and

that five months, at least, are spent as eggs or in

the egg-sacs. Reference to the climographs shows

* » MatM* rainfall

-I" -0-° -

J 4 0 _L50

20

FIGURE II Above: Climograph for Bombay, India, and Btilolo, New Guinea; below, histograms

showing rainfall at study site during the study period.
NUMBER 149 1 /

that the spiders reappear about a month after the

return of waim wet conditions (June) and become

rare during onset of dry colder conditions (December/January).

PREY AND PREY CAPTURES

Taxonomic Range

Little is known of the taxonomic range of prey

caught by Nephila species. Osorio and Moreno

(1943) list 28 species of five orders of insects caught

by N. clavipes in Cuba.

Thakur and Tembe (1956:332) state that near

Bombay the food of N. maculata "consists almost

entirely of butterflies, moths, dragonflies and grasshoppers." Hingston (1922c:918) suggests that the

main prey are nocturnal "moths and flies."

Analysis of the data from prey traps and our

observations over the whole of the Wau area confirm that, as Turnbull (1960) reported for Linyphia

triangularis (Clerck), and we have reported for

Argiope argentata (Fabricius) (Robinson and Robinson, 1970a), the spider is essentially opportunistic.

Whatever is trapped at a particular web site and

proves edible is prey. To illustrate: one observed

spider included several winged phasmids, of two

species, in its diet for a period of about three weeks.

This is the only spider that we know of as taking

phasmids in any quantity. Since we were also

studying phasmids in this area we know that the

web of this spider was built next to the one tree in

the study area that was a food plant used by the

two species. Thus the spider was in a position that

provided it with a resource not practically available

to the others. Similarly one of the sample had,

for some time, a web site close to a colony of large

social wasps. For several weeks this spider caught

wasps of this species, which were not available to

others in the sample.

In general the taxonomic range of prey caught

by N. maculata at Wau was considerable. Analysis

of the prey trap data did not permit division into

taxa lower than the ordinal level in most cases,

since we were dealing with fragments and were not

prepared to devote a major portion of time to their

determination of lower taxonomic categories. Nevertheless, some simple clues were usable; in determining orthopterans we assumed that debris of a

particular green coloration represented tettigonioids rather than acridoids, since the latter were

characteristically brownish in coloration in the

study area. We also knew the coloration of the

predominant butterfly species and were able to

separate these from moth debris when wing fragments were large enough. This background must be

borne in mind when considering our data on the

taxonomic range of prey. (The dried prey fragments are available to any entomologist interested

in working with them, either as a whole or in a

particular order.)

Subsequent tables and figures show the data

grouped into seven orders and the categories "others" and "unidentified." The range of organisms

included in the "others" category are as follows—Araneidae: Gasteracantha species (1), Nephila maculata (3 males and 2 females); Salticidae

(1); Lycosidae (1); Isoptera (2); Dictyoptera: Mantodea (2); Phasmatodea: Eurycnema species (1);

Lepidoptera larva (1); and Dermaptera (1). Some

of the easily identifiable subtaxa within the orders

are as follows—Odonata: Anisoptera; Hemiptera:

Heteroptera, Pentatomidae and Homoptera, Cicadidae; Diptera: Tipulidae; Lepidoptera: Sphingidae;

Coleoptera: Scarabaeoidea, Staphylinoidea, Elateroidea, Cantharoidea, and Curculionoidea; and

Dictyoptera: Blattaria and Mantodea.

Numbers in Taxa

Table 2 shows the total numbers of prey in each

taxonomic category for the whole year. We cannot

reasonably allocate the unidentified remains to

orders by using the proportions obtained in the case

of the identifiable remains because two groups,

the Lepidoptera and Coleoptera, have features

that survive maceration. Insects of these orders are

thus less likely to become "unidentifiable" than are

insects that are fragile and soft-bodied.

Odonates contribute only a small number to the

total identified catch (12). Orthopterans are fairly

low in numbers (199) of which tettigonioids constitute a major proportion (ca. 75%). Grilloids (11)

and Acridioids (30) contribute relatively small

numbers but are probably useful food sources because of their size when able to fly (i.e., when trappable by the spider's aerial web).

Hemipterans (273) are numerically ahead of

orthopterans and the cicadas (139) are at least in
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NUMBER 149 19

the same size range. Lepidopterans make up the

second largest group of identified remains (1442)

and constitute 33.3 percent of these (23.9% of all

prey caught, including unidentified packages). Of

the Lepidopterans, moths (1428) constituted the

largest number; this remains true even if we admit

the possibility of some misclassification in this

category. The preponderance of moths can be

accounted for by a number of factors, one of which

may be a differential potential for web-avoidance

between diurnal and nocturnal insects of this order.

(There are undoubtedly differences in the numbers

of diurnal and nocturnal lepidopterans in the

study area and this point is discussed later). Dip

terans rank third in total numbers (575) and could

be heavily implicated in the unidentified category.

Their importance in the prey-economy of the adult

spider may be less than is suggested by their numbers since very few of those caught in the study area

exceeded 50 mg in weight. Hymenopterans totaled

184 and again may be well represented in the unidentified remains. Ants (74) were principally alates

and catches probably coincided with nuptial flights.

Wasps (25) and bees (32) are low in numbers. The

Coleoptera constituted 37.2 percent of identified

prey and are the insects present in the largest total

number (1610). Of these beetles, those definitely

identified as scarabioids (179) were probably the

heaviest insects caught by the spiders during this

study. Seventeen Dictyopterans were identified

among the remains. Since small adult roaches were

frequently observed at night and represented 12.6

percent of the total number of insects caught on

the sticky traps, they may be an important element

in the unidentified category. In Table 2 they are

listed as "Other orders."

It is very noteworthy that the relative proportions

of the major taxonomic groups that constitute the

spider's prey vary very little between the ten individuals that constituted our sample. (This relative

constancy is even more remarkable when it is considered that spiders nos. 1-10 were not the same

individuals over the year.) Table 3 gives the proportions of the total catch that were made up by

insects of the orders Lepidoptera, Coleoptera, Diptera, Orthoptera, Hymenoptera, Hemiptera, and

Odonata plus unidentified and "others." The greatest range of variation is in the "unidentified" category.

Temporal Distribution

Figure 12 shows the distribution of the proportions of prey numbers, by the same categories used

in Table 2, divided between the six driest and six

wettest months of the year.

The overall total for the six wettest months

(October, November, December, January, February, April) is less than that for the six driest months

(March, May, June, July, August, September) but

not markedly so (2586 against 3453).

Numbers of orthopterans, dipterans, lepidopterans, hymenopterans, and coleopterans are all

higher in the dry months than in the wet months.

Hemipterans are higher in numbers in the wet

season. The total weight of prey caught in the wettest months exceeds that caught in the driest

months—at least on the basis of the weight of

prey residues: 58.674 grams (47.5%) against 64.87

(52.5%) for the wet months.

The fluctuation in weekly total catches for the

major (ordinal) categories can be seen from Figure

TABLE 3.—Percentage composition of prey per spider plus composition of insects caught by window-pane

and sticky traps (total prey sample=6039)

Prey

Odonata

Orthoptera ...

Hemiptera ...

Lepidoptera .

Diptera

Hymenoptera

Coleoptera ...

Other orders

Unidentified

Spider

1 2 3 49

(N=6J9) (N=*

6 7 8

(N=601) (N=48i) (N=6S8)

9 10 Mean W. P. Sticky

(N=612) (\=69J) percentage trap trap

0.2 0.4 - 0.2 02 0.2 0.4 - 0.4 05 0.01

3.6 2.S S.9 2.2 2.0 4.0 4.7 3.8 4.6 2.5 3.3 0.8 1.0

4.4 4.8 3.7 3.7 4.6 5.7 3.6 3.9 7.6 42 4.5 7.5 8.1

245 25.9 20.1 23.9 23.0 23.2 21.2 21.2 22.9 305 23.9 23.1 1.7

9.5 9.3 8.2 10.1 10.0 9.3 7.7 8.9 12.8 7.4 9.5 26.6 11.2

2.4 3.0 2.7 2.9 3.3 2.9 3.8 4.4 2.8 2.9 3.0 9.6 5.0

28.6 25.5 30.6 23.6 24.8 23.0 29.7 32.9 25.4 19.6 26.7 26.5 55.6

0.S 1.4 0.7 - 0.8 0.8 0.2 0.7 - 0.6 0.54 5.8 17.2

26.4 27.7 29.7 33.3 31.1 30.7 28.8 23.7 23.8 31.9 28.3 - 0.2
20

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

.00%

5 0 -

•

ma.

L

DIP.

i\ OIC. OIHIi

TOTAL

WIIOHT

FICURE 12.—Percentage composition of prey, by orders, divided between the six driest months

and the six wettest months.

13. Note that the Odonata, Orthoptera, Diptera,

Hemiptera, and Hymenoptera are absent from

some weekly catches, whereas Lepidoptera and

Coleoptera are always present. Table 4 gives

monthly totals for the entire year and is comparable

with Table 2 of Robinson and Robinson (1970a:

350). From this it will be seen that two orders, represented by low total numbers, are absent from

identified catches in some months. Thus odonates

are absent in January, March, April, October, and

December. Dictyopterans are absent in April, June,

July, and December.

Within some of the more numerous orders there

are absences of subgroups in certain months. Thus

within the Orthoptera identifiable gryllids were

present only in September, October, November,

December, with more than half the total being

caught in October (a wet month). Tettigonioids

were caught in all months, but three months (July,

August, and September) account for more than half

the total catch. The acridoids were absent in

identifiable remains for the months of February,

April, May, August and October, and two months

(March and November) account for more than half

the yearly total. Some hemipterans were present

in all months, but the large and conspicuous cicadas

(suborder Homoptera) were caught in all but one

(October) of the six wettest months and only two

(March and May) of the six driest months. More

than half the total yearly catch of cicadas occurred

in two months: April and November.

Lepidopterans were caught in all months but of

the positively identified butterflies (13) eight were

caught in four of the driest months (March, May,

July and August) and five in four of the wettest

months (November, January, February and April).

More than half the yearly catch of moths was

caught in five successive months (April, May, June,

July, August).

Monthly totals of dipterans vary between 11

(December) and 95 (August) and similar totals for

Hymenoptera between 7 (February) and 32 (May).
NUMBER 149 21

•Oth

inches

•Mks

"S iS~

FIGURE 13.—Weekly distribution at study site of numbers of

prey, by order, against rainfall.

Total catches lor coleopterans range from 99 in

April to 164 in January. The large scarabaeoid

beetles appear in large numbers in September, and

172 out of the year's total of 179 are caught in this

and the succeeding six months. This period includes

the weeks of highest average weight of unit prey

remains.

Numbers of unidentified prey remnants vary

throughout the year and constitute 28.3 percent ol

the yearly total. In the six driest months the total

is 1040 against 672 for the six wettest months. The

difference, 368, is approximately 21 percent of the

total. The highest number of unidentified remains,

237, occurs in August and the lowest, 71, in December.

Weights of Prey Remnants

The total weight of the prey remnants collected

in the prey traps was 123.544 grams. The weekly

distribution of the weights that make up this total

are given in Table 2 alongside the average weight

per unit prey (obtained by dividing the weight by

the total number of prey items, identified and unidentified). What this figure may represent in

terms of live weight is discussed in the section on

energetics (page 33). It is more than half of the

estimated live (wet) weight of prey caught by a

sample population of Argiope argentata in one year

(Robinson and Robinson, 1970a:349).

Of this total weight 64.87 grams (52.5%) were

the contribution of the six wettest months and

58.674 grams (47.5%) were collected in the six

driest months. The highest weekly totals occur in

October when, in two successive weeks (23 and 24),

the totals exceeded 4.6 grams. Totals of over 4

grams occurred in one week (19) in September

and one week (25) in November. In fact in the

7 weeks commencing 23 September and ending 10

November, the prey remnants totaled 29.563 grams,

23.9 percent of the yearly total! This was also a

period of high average weights of prey remnants

(all averaging over .03 grams per unit). This suggests that some large prey item is seasonally available to the spiders. This is borne out by the fact

that scarabaeoid beetles feature prominently in the

catches for these weeks. Melolonthids, in particular,

were recorded in enormous numbers at light during

this period and featured heavily in prey-trap re-
22

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 4.—Monthly totals of insects caught by mature Nephila maculata

sample (N=10)*

Prey Jan. Feb. Mar. Apr. May June July dug. Sept. Oct. Nov. Dec. Total Percent

Odonata

Orthoptera

Grylloidea

Tettigonioidea

Acridoidea

Subtotal ...

Hemiptera

Heteroptera ....

Homoptera ...

Cicadidae

Subtotal

Lepidoptera

Moths

Butterflies

Larvae

Subtotal

Diptera

Nematocera

Brachycera &

Cyclorrhapha ...

Subtotal

Hytnenoptera

Ants

Wasps

Bees

Subtotal

Coleoptera

Scarabaeoidea

Elateroidea

Cantharoidea

Curculionidea

Subtotal

Dictyoptera

Blattaria

Other orders

Unidentified

Grand total .

Percent caugh

per month

1

1

2

5

3

19

27

84

1

85

46

1

10

147

15

1

1

164

1

S

1

16

20

136

1

137

31

7

123

11

134

8

9

17

3

5

8

16

92

94

52

12

173

4

1

178

1

19

2

11

2

34

129

2

1

132

56

3

47 31 52 59

1 1 2 6

11- 1

8 5 10 8

15

92

99

4 3 2 -

4 2 1 2

97 142 13S 77

440 479 505 419

5

9

12

5

3

29

229

1

2

73

15

4

10

3

32

119

3

12

2

136

3

1

10

1

12

3

1

3

7

172

230 172

67 62

4

62

6

2

5

2

15

141

3

2

1

1 3

151 177

661 597

23

4

28

1

3

140

2

142

58

17

75

4

1

8

2

15

136

1

146 137

174

575

33

2

f>

109

3

112

82

13

95

o

5

2

3

12

125

127

237

625

2

31

1

34

5

2

1

8

94

94

39

2

41

6

4

13

7

30

69

41

2

1

!68

490

6

II

17

6

1

1

8

98

98

8

2

6

16

4

2

12

18

97

60

1

113 158

3

2

167

487

1

3

2

20

10

35

3

8

11

32

54

79

1

4

13

6

2

2

10

80

30

1

1

112

118

424

4

1

5

4

14

6

3

1

51

61

66

80 66

8 11

1

II

2

5

1

8

93

11

1

1

106

71

337

12

11

11

147

30

199

62

35

37

139

273

1428

13

1

1442

520

11

44

575

53

25

74

32

184

1395

179

11

21

4

1610

17

15

1712

6039

.18

.18

2.43

.5

3.3

1.03

.58

.61

2.3

23.65

32

.02

23.88

8.16

.18

.73

9.52

.88

.41

1.23

.53

3.05

23.1

2.96

.18

.35

.07

26.68

28

25

28.35

7.29 7.93 8.36 6.94 10.95 9.88 9.52 10.35 8.11 8.06 7.02 5.58

'Numbers on row opposite ordinal name are of prey not identifiable to lower taxonomic levels.

mains. Their emergence is known to be facilitated

by wetting of the ground where they pupate, and

the rainfall in September followed a dry spell

(Figure 13). The catch for the week commencing

23 September (week 19) included 14 cockchafers

which also figure prominently in the following

weeks 20-25 (15, 14, 11, 10, 11 and 5). The catch

for October also included five other scarabaeoids

of more than 20 mm in length. Other contributors

to the heavy average weight during this period

were very large gryllids (page 20).

In all there was one week (week 48) with a total

of less than one gram of prey remnants (April

1971), six weeks with between 1.0 and 1.5 grams,

thirteen weeks with between 1.5 and 2.0 grams, 22

weeks with between 2.0 and 3.0 grams, five weeks

with over 3.0 and less than 4.0, and five weeks with

over 4.0 and less than 5.0 grams.
NUMBER 149 23

We cannot assign weights to the numbers of prey

in each taxonomic division since we were dealing

with prey remnants and it would have been far too

time-consuming to weigh each of the 6039 trash

packages separately. Similarly we were not able to

record size ranges of the prey items (as did Robinson and Robinson, 1970a, when recording prey in

the webs of Argiope argentata). Thus there is no

method of weighing samples and assigning approximation of weights to the numbers of prey in each

taxon. We can make, however, some very crude

guesses about the effect of considering weight, on

the relative importance of the various categories

of prey. Thus, in the case of the orthopterans, it

would be reasonable to assume that most of those

that were caught would be alate adults that could

fly and therefore be more likely to move into webs

sited well above the ground than would juveniles,

which can only jump. We would assume, therefore,

that the relative importance of orthopterans as prey

(3.3% of the total catch) is not likely to be diminished because of below average weight. On the

other hand few dipterans exceed 0.05 grams in live

weight and we would predict that if the weight of

the 575 dipterans caught by Ncphila was known

their contribution to the total catch would be less

than the 9.5 percent calculated from their numbers.

Because the catch of hemipterans includes 139

weighty cicadas (average weight probably above

0.2 grams) we would expect the prey in this category to be more important than their 4.5 percent

by numbers suggests. The two orders providing the

predominant numbers, Coleoptera and Lepidoptera, are, we feel, likely to contribute numbers of

weighty prey and their predominant position is

likely to be reinforced if we considered their contribution to the calories available to the spider.

These considerations suggest that a ranking of

taxonomic categories in terms of "energy bundles"

would read, in descending order: Coleoptera, Lepidoptera, Orthoptera, Hemiptera, Diptera, Hymenoptera, Odonata, and Dictyoptera.

Comparison of the monthly distributions of the

weight of prey with the numbers of prey gives

rise to some interesting observations. The weights

of prey start to rise in August whereas prey numbers fall from this point until December. The

weights reach a peak in October and then fall

through November to December but the December

total is still higher than all the other months of

relatively low weights, except March. The December low point in prey numbers is the lowest of

the year. The rise in prey weights during this

period corresponds to an increase in rainfall to

the year's peak in October (which was also the

month with the largest number of days of rain).

As stated earlier, the period of high weights and

relatively low numbers was one when heavy scarabaeoid beetles were abundantly represented in the

catches and these probably account for the differences cited above.

Comparison with Argiope argentata

As far as we are aware the only study of a spider's

prey over a one year period is that on Argiope argentata (Robinson and Robinson, 1970a). There

have been a number of excellent studies of the prey

of temperate orb-weavers (see Kajack, 1965, for an

extensive bibliography), but the subjects have all

been spiders with a seasonal activity covering only

part of a year. Argiope argentata differs from Nephila tnaculata in being largely diurnal, choosing open

areas for its web sites, having an advanced pattern

of predatory behavior (Robinson, Mirick, and

Turner, 1969), and being considerably smaller and

lighter than N. maculata.

The area where studies of A. argentata were carried out has a much more seasonal climatic pattern

than Wau. At Barro Colorado Island in Panama

there is a pronounced dry season of 3 to 4 months

(total rainfall average 8.2", three months with less

than 3" rain) and a distinct wet season of 8 to 9

months, total rainfall average 98.9". This is not

true of Wau where in only one month (August)

did the total rainfall drop below 3"', and this was

exceptional.

There are major differences between the catches

of the two spiders in taxonomic content and in

temporal distribution. In terms of numbers, hymenopterans constitute the most important prey

item for Argiope with a total of 3304 out of 4672

prey items. This compares with 184 out of 4327

identified prey items in the case of Nephila. This is

70.6 percent of the total prey caught by Argiope and

3.0 percent of the total caught by Nephila. In

terms of weight these hymenopterans constitute an

estimated 18.1 percent of the total caught by Argi-
24 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

ope and are most unlikely to increase their relative importance to Nephila if weight is considered.

Orthopterans were the second most important prey

item, in numbers, to Argiope (11.4%) and constituted only 3.3 percent, by numbers, of the Nephila

catch. In weight, orthopterans rise to the predominantly important prey item for Argiope (55.2%)

and are most unlikely to assume this importance

for Nephila. Of the orthopterans caught by Argiope,

tettigonioids account for 57.4 percent, acridioids

for 41.4 percent, and grylloids for 1.5 percent. The

equivalent percentages for Nephila are 73.9, 15.1,

and 5.5, with 5.5 percent not assigned to superfamily.

Coleopterans are the most important prey, numerically, for Nephila (26.6%) and are probably

the most important prey item in terms of weight.

For Argiope they account for 5.8 percent of the

catch by numbers and an estimated 6.6 percent by

weight. We have not seen Argiope feeding on large

beetles. Similarly, lepidopterans account for 23.9

percent of the Nephila catch and only 2.9 percent

of the Argiope catch, by numbers, and 5.4 percent

by estimated weight. Of the lepidopterans caught

by Nephila 99 percent were classified as moths,

0.9 percent as butterflies and 0.1 percent as larvae.

In the case of Argiope 89.8 percent were butterflies

and 10.1 percent moths.

Of the other orders odonates were caught in small

numbers by both species of spider, Nephila catching

12 (0.2%) and Argiope 48 (1.03%, not 0.14% as

given in Robinson and Robinson, 1970a: 349).

Hemipterans occur in relatively small numbers in

both cases, Nephila catching 273 (4.5%) and Argiope 207 (4.4%). As stated earlier the relative importance of hemipterans to Nephila should perhaps

be increased if we consider that the cicadas are

heavy, and therefore an important source of food

that is belied by their relatively small numbers (139

or 2.3% of the total catch by numbers), Argiope

did not catch large cicadas.

Dipterans account for 9.5 percent of the total

catch of Nephila and 2.4 percent of the catch of

Argiope. Their importance to Nephila is probably

less than their numbers suggest because of their

small size.

Many of the differences between the taxonomic

composition of the prey of the two spiders probably result from differences in habitat, web siting,

and web structure. Of these the first two are probably the most important. The two spiders are undoubtedly catching insects that preponderate in

different proportions in the two habitats, and the

two zones within the two habitats. Robinson and

Robinson (1970a:355-356) discuss the factors that

may influence the catch of Argiope argentata at

Barro Colorado Island. The influences acting to

determine the scope of the Nephila maculata catch,

at Wau, are discussed above.

Differences in the seasonal patterns of the catches

of the two spiders are grossly relatable to differences in the climatic pattern at the two localities. The

effect of the lowland monsoon climate at Barro

Colorado is not entirely clear but there are suggestive data (Robinson and Robinson, 1970a:352-

353). The dry season in Panama is clearly more

inimical to spider activity than the short dry intervals at Wau.

Comparison with Insect-Trap Catches

Kajack's (1965, 1967) studies of the food relationships between spiders and their prey were

based on intensive studies of three species of small

araneids. Prey caught by the spiders was sampled

by removing prey items from the webs and the

abundance of mobile insects was evaluated by using

sticky traps. Kajack found (1967:814) that "the

fauna captured on these traps coincided with those

caught in the webs so that it was possible to regard

the number of insects on sticky traps as an index

of abundance of the potential food of the spiders."

The three species that Kajack studied, Araneus

quadratus Clerk, A. cornutus Clerk, and Singa

hamata (Clerk) are all smallish spiders (Locket and

Millidge, 1953), considerably smaller than Argiope

argentata, and very much smaller than Nephila

maculata. Kajack states (1967:813) that "very small

insects which weigh hundredths or tenths of mg

(from 0.05 to 0.1 mg) constitute the vast majority

of prey caught in spiders' webs." Thus die spiders

Kajack studied caught very much smaller prey than

either Argiope argentata (Robinson and Robinson,

1970a) or Nephila maculata. This point is relevant

to a consideration of how insect sampling techniques can be used to assess the prey available to

the larger tropical orb-web spiders.

Pilot studies that we carried out in Panama

suggested that sticky traps would not adequately
NUMBER 149 25

sample the availability of prey to the larger orbweavers. Many insects seemed capable of detecting

the presence of such hazards and avoiding them.

This view was confirmed by some studies that we

carried out (in conjunction with W. Graney) to

investigate the possibility that insects might detect the presence of apparently much less conspicuous traps such as spider's webs. After various trials

we eventually decided to watch the behavior of

insects flying in the vicinity of a 10 X 5 foot length

of double nylon mist netting that was erected in

the laboratory clearing at Barro Colorado Island.

This was large enough, unlike a spider's web, to

provide a reasonable number of interceptions by

insects in an 8-hour observation period (divided

into half-hour shifts). The net was presumably

more conspicuous than a web but much less conspicuous than a sticky trap. Some insects proved

quite capable of detecting its presence and made

avoidance maneuvers. Thus an insect would fly

towards the net and then, when nearby, rise almost

vertically, fly over the top, and proceed on its flight

path. Other insects blundered straight through the

net striking its threads, while others changed

direction after striking the net. It was interesting

to find that the same species of insect would in one

set of circumstances avoid the net while in the

course of another behavior it would hit it. Thus

large wasps flying on a "beeline" would hit the

net, but when flying erratically from flower to

flower they would miss it and take very obvious

avoiding action. This suggested to us that some

insects might be able to avoid webs. We tried to

test this further in New Guinea by mounting a

Nephila maculata web on the glass of a windowpane trap and operating this next to a normal

window-pane trap. Each day we moved the traps

around and tried thereby to eliminate any position

effect. There were interesting differences between

the catches of these two traps over a 14-day period.

Catches of insects belonging to the orders Diptera,

Hymenoptera, Coleoptera, Lepidoptera, and Hemiptera were all lower in the case of the trap with

the web mounted on the glass. The total number of

insects involved (462 caught by the experimental

trap, 505 by the control) is unfortunately too small

to enable us to determine whether there are any

group* within orders that are less sensitive to

spider's webs than others. We are continuing this

experimentation in other localities.

Our doubts about sticky traps led us to consider

the possibility that window-pane traps might give

a better index of the food available to large spiders

such as Nephila maculata. To test our Panamabased conclusions about the inadequacy of sticky

traps we also used these at Wau. Data from the

traps are of interest in two respects Firstly they

enable a comparison to be made between the

specificity of the web and the specificity of the

traps. Secondly the trap data should reveal any

cycling or periodicity of outbursts within specific

groups of insects, which should be valuable as a

check on fluctuations in the temporal pattern of

occurrence of particular groups of prey.

In fact for the 43 weeks (3 June 1970-30 March

1971) for which we have data from the windowpane traps the three traps caught more insects than

the ten spiders: 7555 compared with 4850. During

the same weeks the window-pane traps caught more

lepidopterans than the spiders: 1743 compared with

1064, and more beetles: 2003 compared with 1342.

The weekly analysis of numbers is given in Tables

5 and 6. (All these figures deal with insects over

4 mm in length; we decided that prey less than

this size would pass straight through the web of

an adult Nephila). On the whole the majority of

insects caught by the window-pane traps was small

and did not include large lepidopterans and beetles

of the sizes that were seen in the spider's webs.

Table 7 details the size distribution of the insects caught by the window-pane traps.

In Figure 14a we have plotted the weekly totals

of prey from the prey traps and insects caught by

the window-pane and sticky traps. From this it will

be seen that there is no obvious correlation, positive

or negative, between fluctuations in the spider's

prey numbers and the numbers of insects caught

by the traps. We have worked our correlation coefficients for total numbers of prey caught per week

by the spiders and insects caught by the windowpane traps. These give no basis for rejecting the

hypothesis of no correlation between the two sets

of results. We believe that there is no correlation

between the two. Similar statistical results apply

to comparing the weekly totals of lepidopterans

and coleopterans caught by the spiders and the

window-pane traps. Interestingly enough the pro-
26

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 5.—Weekly analysis of insects caught in 3 window-pane traps

Prey

Odonata

Hemiptera

Cicadoidea

Diptera

Hymenoptera

Coleoptera

Scarabaeoidea .. .

Elateroidea

Cantharoidea .. .

Other orders

Total

• No traps erected

3»

?

18

.

57

fir.

17

49

1

1

6

4

220

4

1

1

21

2

M

57

18

48

-

-

9

3

195

during

5

1

11

-

411

75

18

45

1

3

18

1

9

231

6

?

8

I

?7

63

38

27

2

4

1

2

175

weeks 1

7

12

|

inn

18

34

1

4

1

3

206

8

1

4

1

46

111

13

26

2

5

_

7

236

and 2.

9

1

8

2

4fi

01

18

19

-

7

1

2

195

10

15

1

51

66

37

31

5

6

_

9

224

11

1

8

-

61

fin

25

15

-

5

_

4

179

Numbers on

12

7

-

31

45

20

IC

1

7

_

3

130

13

20

1

44

63

21

15

4

6

?

2

178

14

20

43

44

9

20

6

6

?

3

153

15

2

11

-

40

20

10

21

G

1

_

6

123

16

1

13

-

50

20

II

20

5

1

_

2

123

row opposite are of

17

14

-

53

33

18

25

3

9

_

2

157

18

2

16

2

46

43

9

30

2

5

1

2

158

19

_

8

3

36

31

16

4G

3

5

_

1

149

20

2

17

-

62

28

17

19

3

8

1

4

161

21

1

10

58

45

14

33

4

?

2

9

181

prey not identifiable

22

1

11

1

54

26

25

17

4

8

2

4

53

to

23

1

14

2

45

19

14

33

5

6

_

12

151

24

,

6

-

29

22

10

35

7

4

1

5

120

25

2

10

2

41

24

20

32

2

6

2

2

14

157

26

2

8

3

S3

25

14

37

6

3

3

19

153

lower taxonomie

levels.

Prey

Orlhopttra . . .

Hemiptera ... .

Cicadoidea . .

Lepidoptera ... .

Diptera

Hymenoptera ..

Coleoptera

Scarabaeoidea .

Elateroidea

Cantharoidea

Dictyoptera ... .

Other orders ..

Total ..

19

SI

.

4

18

11

75

-

14

7

9

10

179

20

4

12

-

6

15

12

72

-

17

6

9

7

160

TABLE

21

1

18

-

5

19

20

44

-

10

5

7 '

14

143

22

,

17

1

1

20

10

64

-

15

6

• 7

2

144

6.—Weekly

23

4

11

-

4

18

4

44

.

14

3

12

17

131

24

_

8

-

6

12

9

47

-

2

7

11

8

110

25

1

5

-

6

13

7

52

_

4

8

9

11

116

26

3

10

-

2

23

10

47

-

9

13

15

6

138

analysis

27

3

10

1

-

10

3

35

.

19

11

9

10

111

28

1

24

7

3

18

II

62

1

11

8

18

12

176

29

4

8

3

1

12

5

58

I

10

6

16

1

125

of

30

_

6

1

9

16

2

35

.

3

9

3

6

90

insects

31

_

17

6

4

17

15

40

2

11

5

9

5

131

32

2

10

-

-

8

5

68

-

8

9

20

I

131

caught

33

1

6

I

-

18

6

74

-

9

11

19

7

152

34

1

8

2

-

14

3

99

3

11

7

35

13

198

35

-

4

-

1

11

56

1

4

5

18

4

105

i n

36

1

(i

1

-

16

5

99

2

9

8

14

5

166

two

37

_

5

-

3

21

5

87

1

10

7

35

5

179

sticky

38

1

6

-

1

13

3

59

-

9

6

19

-

117

59

1

4

-

-

10

4

31

-

13

1

22

1

87

traps

10 41

1

6

1

2

9

3

42

1

6

3

17

3

94

i

4

-

1

8

6

27

-

14

3

30

4

98

42

_

6

-

-

17

5

54

-

8

7

29

6

132

*

13

_

9

-

1

11

7

37

-

6

4

18

6

99

44

_

6

-

-

17

3

49

1

10

5

21

3

115

49

1

5

-

-

12

3

45

-

13

9

15

3

106

Total

2

32

262

24

60

396

178

1502

13

269

179

446

170

3533

Ordinal

Tola

2

32

-

286

60

396

178

-

-

-

1963

446

170

Percent

.06

.9

-

8.1

1.7

11.21

5.04

-

-

-

55.56

12.6

4.8

name are of prey not identifiable to lower taxonomie levels.

TABLE 7.—Size distribution of insects caught in

window-pane traps*

Insects

Odonata

Orthoptera

Hemiptera

Hetcroptera

Homoptcra

Cicadoidea

Lepidoptera

Diptera

Hymenoptera

Coleoptera

Other orders

Total numbers

Total percent ...

<10mm 10-19mm 20-29mm > 30mm Total

1

29

208

175

1245

1899

586

1659

368

6169

81.65

31

56

14

58

451

108

122

326

72

1238

16.40

27

30

47

3

14

17

145

1.92

1

1

3

.04

1

67

264

21b

88

174S

2010

722

2003

441

7555

'Numbers on row opposite name are of prey not identifiable to lower taxonomie levels.

portions of the total catches that were constituted

by lepidopterans and coleopterans are similar when

we compare the spider's prey with the window-pane

traps. The histograms in Figure lib show the percentage of the total numbers constituted by nine

orders of insects in the catches of the spiders,

window-pane traps, and sticky traps. The differences between the catches of lepidopterans and

coleopterans mentioned above are less than 1 percent. The sticky traps, on the other hand, caught

proportionally less lepidopterans (less than 1.7%)

and proportionally more coleopterans (over 55.6%).

These results indicate that very few of the unidentified prey packages obtained from the spiders are

likely to be from lepidopterans or coleopterans; the

proportions of these two orders are thus probably

more truely comparable with the trap data than

with those for other orders, which might be altered

if the unidentified prey could be assigned to orders.

Since we know that the spiders are catching larger

insects of several orders than are the window-pane

traps, and catching them at different times, the
NUMBER 149 27

Prey

Diptera

Hymenoptera

Coleoptera

Scarabaeoidea .. .

Elaceroidea ... .

Cantharoidea ..

Dictyoptera

Other orders

Total

27

6

. 14

3

. 47

. 19

. 12

. 41

3

5

5

7

. 162

28

4

n

3

VI

V,

18

41

-

13

2

8

13

173

29

•\

1?

<;

n

12

42

1

8

10

5

11

154

"0

f)

?*>

4

r

>

->n

23

58

-

6

13

8

4

238

31

?

">\

7

r

iR

78

30

69

1

6

13

6

5

296

32

1

7

53

8->

19

01

-

2

8

6

4

246

TABLE

33

5

3

•>r.

11

22

40

-

5

13

6

1

173

34

<>1

4fi

12

51

-

6

15

6

7

171

5.— (Continued)

35

R

1

?

r

>

4fi

15

31

1

2

7

8

7

151

36

<>

6

3

49

7?

16

53

1

3

7

3

8

223

37

15

fl

11

47

12

33

-

5

8

7

1

167

38

?

1

''fi

48

16

52

1

6

11

5

4

177

39

15

r.s

45

18

55

1

7

5

6

7

230

40

I

11

1

41

34

15

38

1

6

7

6

24

185

41

R

1

%?

13

31

2

9

11

4

13

152

42

14

4

?q

u,

10

25

-

4

12

5

14

153

43

I

1?

4

17

?1

7

17

1

4

13

3

28

132

44

|

11

1

21

?T

13

36

-

4

5

2

11

130

45

8

1

11

??

9

22

-

12

5

2

20

134

Total

67

480

88

1743

2010

722

1491

14

190

308

121

320

7555

Ordinal

total

67

568

1743

2010

722

2003

121

320

Percent

89

7 52

23 07

26.6

9.56

26.51

1.6

4.24

similarity in proportions of lepidopterans and

coleopterans is in all probability merely a strange

coincidence.

The difference between the sticky traps and the

window-pane traps in the proportions of these two

groups of insects is probably significant in terms of

trap specificity. The low catch of lepidopterans by

the sticky traps could be because these insects

either (1) can detect the presence of the sticky

trap and avoid it more readily than they avoid a

window-pane trap, or (2) can escape more readily

from a sticky trap than from a window-pane trap.

While (1) is possible even when the vast majority

of the lepidopterans involved is nocturnal moths

(the level of illumination on many nights may still

permit visual location or detection of traps) nonetheless (2) is an attractive hypothesis. It is attractive since both the spider's web and the sticky

trap employ a similar method of initially arresting

the insect in flight—an adhesive—and lepidopterans

are known to have a high escape potential from

spider's webs (page 64) and should have a high

escape potential from sticky traps. It is tempting

to think that part of the difference between the

spider-prey results and the sticky-trap results is

due to the active presence of the spider on its trap.

The differences in the proportions of beetles

caught by the spiders, the sticky traps, and the

window-pane traps can be explained in another

way. We can assume that the spiders and the

window-pane traps both lose a number of beetles

that are caught by the sticky traps. The spiders lose

small beetles that strike the web and are either

ignored because they are too light, or which are so

small that they pass through the wide mesh of the

web. The window-pane traps presumably lose some

beetles that are strong enough to. crawl out of the

water after they have been knocked down by impact with the glass. The sticky traps catch both

small and fairly strong beetles. Very strong beetles

escape from them.

From these results and the considerations detailed on page 25, we are convinced that neither

type of insect-sampling device is adequate for the

purpose of assessing the availability of prey to large

orb-weaving spiders. Our light trap certainly

brought in some of the types of large prey that the

spiders caught, but again it is known that the responses of insects to ultraviolet light are confined

to certain groups of the many nocturnally active

animals (Southwood, 1966:200-201, for comments

on reliability).

Rejections of Trapped Insects

Rejection of distasteful or otherwise obnoxious

insects occurs, in most cases, after Nephila has bitten

into the prey. It is then pulled out of the web and

cast away from the plane of the web and falls to

the ground. This treatment, in most cases, damages

the insect. When a prey is detected as obnoxious

before being bitten, it may be left for some time

in situ without being bitten. It is almost always

removed from the web, however, at some stage

during "housekeeping" activities (when particles of

plant material that blow into the web are also

removed). This type of rejection also involves rough

handling by the spider, and the prey is often pulled

from the web in the jaws. Thus, in both cases, the

rejected prey may be damaged and wholly or partly
28

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

MR TRAPS

WIEKS

5 O -

0, B .

• •

Hyn

Ah

FIGURE 14.—a, Distribution of weekly totals of prey caught by spiders, and insects caught by

window-pane traps and sticky traps; b, percentage composition of catches by spiders, by orders,

window-pane traps, and sticky traps. Top portion of "others" category demarcates Dictyoptera

from the remainder.

immobilized as a consequence. From an early stage

in our sampling of the spider's prey we were aware

of the presence of numbers of dead but intact insects

in the prey traps. Conspicuous among these were

lycid beetles, which are known to be obnoxious to

a range of predators (Linsley, Eisner and Klots,

1961), and it seemed probable that these lycids had

been caught and rejected by the spiders. Experiments showed that the spiders did in fact reject

live lycids and we therefore decided to assume

that all the intact (=undigested) insects found in

the prey traps were rejects unless there were strong

indications to the contrary. As it turned out the

great majority of the insects so classified were apose-
NUMBER. 149 29

matic and therefore, unless they were Batesian

mimics, obnoxious in some degree. (We are not

suggesting that the spider is responsive to the coloration of the prey but merely that this is a confirmatory piece of evidence.) Perhaps a proportion of

the insects classified as rejects died in the vegetation

above the prey traps and fell in, but this seems to

be a very small possible source of error since

corpses of known innocuous groups are extremely

rare.

Of the total 371 specimens rejected during the

study year, their composition was as follows: Lepidoptera, 16; Neuroptera, 18; Coleoptera: Lycidae,

198; Hemiptera: Heteroptera, 12; Homoptera, 79;

Diptera, 37; Nephila males, 2; Phasmatodea: Eurycnema species, 2; Hymenoptera: Ichneumonoidea,

1; Unidentified, 6. The 371 total represents 0.3 percent of all the insects found in the traps. Of the

rejects, coleopterans account for 53.3 percent, of

which the lycids account for the great majority.

Hemipterans rank second (24.5%) of which the

majority were homopterans. These have not yet

been identified but were bright blue in color. Roth

and Eisner (1962) do not list any identified repugnatorial secretions from the homopterans, but

many are known to produce waxy secretions which

may be defensive. The heteropterans included pentatomids and reduviids, the former certainly produce defensive secretions and many of the latter

have a painful bite. Neuropterans were present in

small numbers (18) as were lepidopterans (16).

Lacewings are known to produce odors and some

forms have eversible abdominal glands (Riek,

1970:477). The "unidentified" 6 specimens include

cockroaches, phasmids, and flies.

Lycids were rejected in all but six weeks of the

year and theii absence on these occasions seems to

be quite random. This is of interest since Turnbull

(1960) showed that the spider Linyphia triangularis

(Clerck) would accept prey items at some stages

in the season that were unacceptable at others. We

have no data to suggest that lycids were acceptable

at any stage.

Bristowe (1941:262-220) has surveyed the information available on food of spiders in great depth.

He notes that coccids and aphids are either rejected or "accepted with hesitation," but that other

homopterans are for the most part accepted by

spiders. He also states that lacewings are rejected

by most spiders. Among the Diptera he notes that

sciarids, cecidomyids and empids are sometimes

rejected. Flies that we identified as bibionomorphs

(i.e., closely related to the above flies) were certainly among those rejected.

KLEPTOPARASITES

Numbers and Nature

Theridiid spiders of the genus Argyroides are

frequently associated with orb-web spiders. They

build their apparently unstructured complex of

threads close to the plane of the host web and move

about these and onto the host web. They have been

generally referred to as inquilines. However this

term has been used in such a variety of meanings

as to be imprecise and we think that the term

kleptoparasite is more appropriate.

We have conducted studies of the relationship

between Argiope argentata and its kleptoparasites,

and decided that since Nephila maculata seemed to

have a large number of these theridiids associated

with its webs further study would be worthwhile.

Fr. Chrysanthus has identified at least two species

from the material that we sent him and other

specimens remain unidentified. Kleptoparasites of

Nephila maculata include at least the species Argyroides argentatus Cambridge and Argyroides miniaceus (Doleschall). Of these the former was also

found (by Dr. Y. D. Lubin) in the web complex

of Cyrtophora moluccensis, which suggests that it

may not be host-specific.

At the start of our study we counted the kleptoparasites present in 86 webs of adult N. maculata

within an area of about 500 meters around the

study area. We also counted the kleptoparasites on

an equal number of webs belonging to immature

N. maculata whose sizes ranged from 20 to 38 mm

in length. The total kleptoparasite "load" for

adults was 236, and for immatures 129. Of the

adult webs 23 out of 86 had no kleptoparasites

(27%). The juvenile webs contained kleptoparasites in all but 28 (32.5%) cases.

At each morning's web census we counted the

number of kleptoparasites present in the ten Nephila samples. Figure 15 shows the fluctuation in the

weekly totals. The variation is from 35-112, the

average number per web per day is 0.92. This, when

one considers that such tiny spiders could easily
30 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

too

I

IO 2O

I

30

I

4O

I

BO

FIGURE 15.—Weekly fluctuations in numbers of kleptoparasites present on the sample Nephila

maculata webs.

be overlooked, is suggestive of a fairly regular

relationship. Fluctuations in the weekly totals of

kleptoparasites do not seem to be correlated with

such factors as fluctuations in rainfall, number of

days of rain, weight of prey, or numbers of prey.

The maximum number of kleptoparasites that we

recorded on any one web, on one day, was fifteen.

Activities

Unlike Argiope argentata and many other araneids, Nephila species do not store or leave food at

the capture site after it has been immobilized. All

prey is carried from the capture site and stored at

the hub region (Robinson and Mirick, 1971). This

aspect of the predatory behavior of the host means

that the kleptoparasites are not able to steal food

from the capture sites as has been described for

the kleptoparasites of A. argentata (Robinson and

Olazarri, 1971:35). On the other hand the theridiids

often move from their "waiting positions" around

the web and down to prey as it is being attacked

by the host. We have seen the theridiids moving on

the surface of the prey and apparently feeding

there while the host is administering the biting

attack (which may last several minutes). When the

host starts wrapping the prey, after the bite, the

kleptoparasites move off to their complex of threads

above the surface of the host web, or below it on

their drag lines. This sort of feeding, during the

host's attack, is not without risk and we have seen

the kleptoparasites become enswathed in silk, alongside the prey, as the host wrapped the prey package.

Because the maze of threads built by the kleptoparasites is in contact with the host web at various

points we suspect that the theridiids may be alerted

to the presence of prey in the web by vibrations

produced as a result of the activities of the host

and/or the struggles of the prey. Those theridiids

actually standing on the host web could be expected

to locate the source of the alerting vibrations more

rapidly than those waiting on their own structures

outside the web. We have not been able to demonstrate this.

In other cases, after the host has transported the

prey to the hub and has commenced feeding, the

kleptoparasites approach and move onto the prey,

often climbing down the silk thread by which the

prey is secured to the hub. They also behave in the

same way towards prey stored at the hub. Figure

16 shows three kleptoparasites feeding on the same

prey as the host and one feeding on a stored prey

item. Stored prey usually become the object of

stealing sensu stricto. Kleptoparasites attach lines to

stored prey and then move up into their own thread

complex, dragging the prey with them. We have

seen prey several hundred times the weight of the

theridiids stolen in this way. Once the thread
NUMBER 149 31

FIGURE 16 Adult female, Nephila maculala, and four kleptoparasites (numbered) feeding on prey.
32 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

attaching the prey to the host web is severed the

host appears to be incapable of detecting its location. Nor does the host appear to be alerted by

the sudden loss of weight that occurs when the prey

is removed from the web. On the other hand we

have seen hosts apparently searching for missing

prey packages hours after they have been removed.

The kleptoparasites give no convincing evidence of

cooperating to remove large items of prey although

they are apparently tolerant of each other as they

move around on the surface of large prey packages.

The host spider does not often react to the presence of kleptoparasites when they are merely moving about on its web. We have only one record,

from many hours of observation, of the host leaving

the hub and attacking a kleptoparasite. This was

bitten and carried back to the hub where it was

wrapped into the prey package on which the spider

was already feeding. Robinson and Olazarri (1971:

35) observed Argiope argentata attack and kill

theridiids that were removing prey from capture

sites. Host spiders, from time to time, become

aware of the kleptoparasites moving about on the

prey on which they are feeding and respond by

making vigorous brushing movements around the

periphery of the prey with their legs. This is quite

a different behavior to that ensuing from movements of the prey within the prey package. When

the latter occurs the spider usually continues feeding but occasionally rewraps the prey in silk.

Colonization of Host Webs

Kleptoparasites may remain in association with

a host web for up to three or four days after the

host has gone. This lingering on could be adapative

since our studies have shown that temporary absence of a host spider from a web site is not unusual. In fact, spiders leave their webs, lay eggs,

and then return to the same site—and sometimes

the same wel)—after one or two days absence. Also

during periods of heavy rain the spiders may spend

one or two days out of their webs hanging under

nearby leaves. New host webs are colonized with

surprising speed and we have recorded up to five

kleptoparasites in the web of an adult Nephila 48

hours after it has moved into a web site that had

been unoccupied for several weeks. This occurred

even in areas where the host species had been completely absent for months. If, as we have suggested,

the kleptoparasite is not strictly host-specific, it

could operate by moving onto any araneid web that

it detects and remaining there when conditions are

satisfactory. Presumably an intermittent supply of

food would constitute a reward.

General Considerations

It is difficult to assess the role of the kleptoparasites in the energy economy of the host. If we

assume that a host may support four or five kleptoparasites throughout most of its adult life their

combined wet weight would certainly not exceed

40 mg. Assuming that dry weight is 40 percent of

wet weight this gives a dry weight of spider at

16 mg. Taking a metabolism figure of 27 calories

per gram per day for spiders, based on the perhaps

more active lycosids (Macfadyen, 1963:234), we get

a daily intake of 0.43 calories per day by the kleptoparasites. How much of this would be available

to the host, in their absence, is difficult to assess.

All of the energy in food that was actually stolen

would be a debit. However, a proportion of the

energy taken from a source on which the host was

feeding could be inaccessible to the host, since the

kleptoparasites may be able, because of their small

size, to extract food from prey structures such as

thin legs, that the host cannot cope with because

of the great size of its chelicerae. We have also

observed scavenging behavior by the kleptoparasites, toward very small prey that become caught

in the web and which the host ignores. This type

of feeding may occur without loss to the host and

could contribute to satisfying the energy requirements of the theridiids.

It is extremely difficult to assess the importance

of a possible loss of 0.43 calories per day to the

host, since this may vary according to the abundance, or lack, of prey from day to day.

Robinson, Mirick, and Turner (1969:492) suggest that Nephila clavipes does not store food at

capture sites in order to prevent it from being

stolen. If food were stored at these sites it might

be particularly vulnerable to attack by kleptoparasites whose activities would be difficult to detect

because of the large area of the web. Our studies

show that Nephila maculata still supports a considerable number of these parasites, even though,

like N. clavipes, it stores food only at the hub.
NUMBER 149

ENERGETICS

From the dry weight of prey residues it is possible to calculate, albeit crudely, the approximate

energy input to each "average" spider. We know

from our own tests that araneids can absorb up to

78 percent of the wet weight of prey, such as domestic crickets. This leaves a minimum of 22

percent to be accounted for in undigested material,

unabsorbed water, and undigestible skeletal material. If we, therefore, assume that 20 percent of the

wet weight of an insect is accounted for by undigestible cuticular structures, we can calculate back

from our figures for the dry weight of prey-remains

to the original wet weight. We believe that the

degree of approximation involved is not greater

than that involved in many calorific input calculations, and that an assumption of 20 percent of the

total wet weight for exoskeleton errs on the generous

side. If the total dry weight of prey-remains for the

year, 123.544 grams, represents 20 percent of the

wet weight of the insects from which they were

derived (residual water having been driven off by

the drying process), then the original prey weighed

617.7 grams. If we assume that 60 percent of this

is water (one of the widely used crude approximations), then the dry weight of skeletal material plus

food is 247.08 grams. Deduct the weight of skeletal

remains and the sources of calorific input become

123.5 grams. If we assume an assimilation efficiency

of 46 percent the result is 56.8 grams per year dry

weight intake, or 5.68 grams per spider, yielding

0.015 grams per spider per day. Assuming that insect material averages 5000 calories per gram dry

weight this gives 75 calories per spider per day, or

for a 3-gram spider, 25 cal/gram. This is less than

we calculated for Argiope argentata—40 cal/grams

(Robinson and Robinson, 1970a:354). However, in

view of the approximations at several stages in the

calculation the differences are probably not important (Macfadyen, 1963:234, gives a metabolism

figure of 27 cal/grams for Araneae).

PHENOLOGY

Spiders that have been studied from the standpoint of ecology have, so far, been highly seasonal

(North Temperate studies) or present throughout

the year but with a distinct period of reduced numbers and reduction of prey intake during a marked

seasonal shift in climate (Argiope argentata at

Barro Colorado Island). The Wau area is clearly

one where year-round activity is possible and in the

twelve months covered by our study no major variations occurred at micro- or macro-climatic levels,

at least within the study area. Adult and immature

female N. maculata were present throughout the

year and so were males. Egg-laying occurred

throughout the study period and at no stage did

prey captures fall to a level that suggests serious

shortage of food. This is in marked contrast to the

situation at Barro Colorado where the spider population fell to nil at one period of the dry season

and there was a very pronounced fall in prey

captures preceding this.

Since the species is markedly seasonal in other

parts of its range (Thakur and Tembe, 1956) it

seems reasonable to assume that the ultimate factor

must be climatic. It is interesting to note that in

the woodland fringe habitats, represented by

transects 1 and 2, adult spiders were absent for

large portions of the year. On the higher altitude

transect 3 (forest fringe) no adult female Nephila

maculata were recorded during the entire year although there was a regular occurrence of spiderlings

and immatures (Robinson, Lubin, and Robinson,

in prep.). Since there were no major changes in the

phytophysiognomy of these areas capable of affecting adult web sites during the study period, we are

inclined to believe that they are susceptible to

greater fluctuation in climatic conditions than the

woodland and forest habitats. They are thus a

fringe area for those spider species that require

woodland or forest conditions. When conditions

favor the survival of adult and immature N. maculata in the fringe areas, conditions in the adjacent

forest should be optimal or nearly so. This hypothesis is borne out by the fact that the massive increase of immatures and males on transect 1, coincides with a similar increase in males, and males

on females, in the study area, and furthermore

overlaps the period when the spiders in the study

area were just past the period of maximum prey

captures (by weight). This period was one of relatively high rainfall.

Despite the overall lack of major seasonality in

the biology of N. maculata at Wau—reflected in the

presence of adults throughout the year, continual

mating and egg-laying, and the results of the col-
34

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

lection of discarded prey—there arc temporal fluctuations in the composition of prey and the presence of males that are of interest. The fact that

there is a marked seasonality in the occurrence of

melolonthids in the prey traps may be associated

with the fact that the immature stages of these

insects probably occur in grassland soils where the

variations in moisture content may be more extreme than in the woodland areas. Cicadas too

seem to occur most frequently in the wetter months.

Other examples of seasonality in prey composition

have been noted earlier (pp. 19-21). These and the

very great increase in the number of males found

on females' webs during the wetter months may be

fluctuations peculiar to the particular 12-month

period in which we carried out our study and much

more extensive studies are, of course, required to

elucidate long-term trends.

In considering the relationship between the variations in the biology of Nephila maculata that

occur over time, it became apparent that attempts

to correlate them with simple climatic and/or biotic

factors are fraught with complications. Some of

these are detailed later in the "Discussion."

Behavior

In the section on predatory behavior we have

included details of comparable behavior patterns

that we have studied in other species of Nephila

and the related genera Nephilengys and Herrenia.

This inclusion of comparative material was carried

out to avoid the fragmentation of an essentially

synthetic approach to the predatory behavior of

these species. Such a procedure has lead to some

repetition, particularly since it seemed useful and

necessary to include cross references to other species

in both the section on behavior units and that on

behavior sequences. We have included a final comprehensive section to tie together the data on predatory behavior.

TERMINOLOGY

Except in the cases of newly described behavior

units, terminology follows that of Robinson (1969)

as expanded by Robinson and Olazarri (1971).

The term "courtship" is here used to include

all the regularly occurring interactions between the

adult male and the adult female that precede the

act of insemination. Morris (1956:128) has defined

courtship as "the heterosexual reproductive communication system leading up to the consummatory

sexual act," including in this definition precopulatory behavior between the two sexes. The term

"mating" is applied to varying ranges of sexual

behavior by different authors. With specific reference to spiders Alexander and Ewer (1957:311)

seem to use the term to cover both sperm induction

(charging the pedipalps with sperm) and insemination, although confusing matters by later referring

to the "actual mating." Bristowe (1941:461-502)

includes sperm induction, courtship, and copulation under the general heading of mating habits.

Our inclination is to treat the term as synonymous

with copulation but to use the latter term in descriptions.

SEXUAL BEHAVIOR

Finding the Female

We have no data on how maies find females. It

seems reasonable to assume that they could simply

locate the females by locating their webs. Certainly

they tend to aggregate on these webs in considerable

numbers, and even spend long periods of time on

the webs of subadult females. Bristowe (1941:467)

concludes "most, and probably all, male spiders

possess a sense which enables them to recognize the

female's proximity without seeing her . . . [by

touching] the web she has spun either in the form

of a snare or a retreat cell."

Our observation that males will remain in the

web of a subadult female after locating it (this is

also true of males of Nephila clavipes, Argiope

argentata, and other Argiope species) suggests that

some property of the silk, rather than a specific

chemical property of a female in reproductive condition, may mediate the first stage in the location

of a potential mate. On the other hand it remains

possible that all females produce a chemical signal

of some kind, and that this is species-specific. In

the course of constructing a web this substance

could be transferred to it and thereby label the

structure. Males will remain on a web for several

days after the female has left it. This, like the similar behavior of kleptoparasites, could be adaptive
NUMBER 149 35

since females often return to the same web after

an egg-laying excursion.

Courtship

The whole subject of courtship in spiders has

been the subject of considerable controversy, some

of which involved hair-splitting quibbles about

terminology. Bristowe and Locket (1926) proposed

a theory of courtship that involved a dual function; suppression of predatory behavior in the female by "male recognition" and, stimulation of the

female to the point of accepting copulatory attempts. Savory (1928) attacked this theory as being

too complex and attributing powers to the spider

that it probably does not possess. He proposed to

regard courtship as a chain of related instinctive

actions in which predatory urges become suppressed

and physiological changes are induced in the participants. Crane (1949) takes an essentially similar point of view on the main issues. Platnick

(1971) argues that all these authors rightly stress

the role of courtship in suppressing cannibalistic

tendencies, but present courtship as a one-sided

activity by which the male affects the female.

Actually Savory (1928:220) noted that "the male

himself becomes more stimulated as courtship proceeds." Platnick (1971) applies a releaser theory

derived from Tinbergen (1954) to spider courtship,

suggesting that the behavior has four functions:

synchronizing mating activities, orienting the individuals, suppressing nonsexual tendencies, and

insuring species-specific mating. Morris (1956) in

an extensive treatment of the function and causation of courtship in vertebrates (mainly fishes)

suggests that the conspicuous, all-absorbing nature

of many courtship ceremonies makes them dangerous to the participants and they must, therefore,

have a strong selective advantage. He suggests four

functions: finding a mate, finding a mate of the

right species, stimulating the mate, and synchronizing reproductive arousal.

These categories differ from those of Platnick in

including mate attraction (finding a mate) and not

including the suppression of nonsexual tendencies

(although that is implied in Morris's category of

arousing the mate). Bastock's (1967) survey of

courtship suggests that there is no single answer to

the question of function and that this varies with

the circumstances. It is clear from Morris' (1956)

description that attracting a mate may be accomplished by using signals effective in one or several

sensory modalities. One of the most valuable ideas

to come out of the reaction chain views of courtship is that these, by the number of steps that they

involve, are fail-safe systems of insuring that mating

occurs between members of the same species (Morris, 1956:130).

Descriptions of the courtship of Nephila species

are limited. As far as we are aware they include

studies of Nephila madagascariensis by Bonnet

(1930), Gerhardt (1933), Charezieux (1961), and

some observations on Nephila maculata by Fischer

(1910a,c), Hingston (1923), and Thakur and Ternbe (1956). There are also some notes on the courtship of Nephila plumipes published by McKeown

(1963).

Fischer (191Oa:527) describes the insertion of the

embolus after the male had struck the genital aperture "by alternate, rapid pecks of the palps, much

as the fingers strike the keys of a typing machine,"

a graphic and accurate description. He did not see

the process of sperm induction or any courtship.

He notes that in one case there were five males on a

web and that a male climbed stealthily onto the

abdomen of a female only to be brushed off by the

female as he approached the "vulva." Hingston

(1923:74) describes the males, the position they

adopt on the female web, their dependence on

food caught by the female, and their tactics in

escaping from females that chase them. He also

describes a highly specialized position that the

female adopts during copulation. In this the female

leans away from the hub of the web by releasing

all the legs on one side "the object being to lay

herself open so as to receive without obstruction

the advances of her mate."

Thakur and Tembe (1956:331) note that the

males aggregate on the webs of females, and remain

there until the female is "ready for copulation."

These authors give no details of the approach behavior nor do they describe the act of copulation

but they do note that "the male does construct a

web on the back of the female, but this is not

used for the transference of seminal fluid from the

genital organs to the receptaculum seminis situated

in the palpus." This paragraph shows that these

authors saw, but largely ignored, a behavior that
36

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

constitutes a phase of courtship that is of long

duration in most of the cases that we have seen.

Charezieux (1961:375) refers to a long period

spent by the male in tentative, hesitant, approach

behavior. This the "travaux d'approche" may last

30-36 hours. During this time the male repeatedly

approaches the female across the web, touches the

apex of the female's abdomen and retreats, eventually climbing onto the abdomen of the female,

moving along its ventral face and copulating. In

the approach phase the male was seen to vibrate

the female's web "as if to check the responses of

the female from a distance" ("comme s'il voulait

se rendre compte a distance des reactions de la

femelle.") Charezieux (1961:378) also states that the

female eventually becomes torpid.

Mrs. Lowry's notes (in McKeown, 1963:147-148)

on Nephila plumipes include the following points:

the male may live on the female's web for weeks

at a time; the male moves to the hub when the

female vacates it and moves away when she returns;

and he approaches the female along her drag line

when she is feeding. The male eventually climbs

onto the ventral face of the abdomen but retreats

if the female shows signs of activity. Lowry eventually saw copulation occur when the female was

torpid and after the male had tapped her body in

several places.

Our observations on the courtship of Nephila

maculate show that it contains elements of the

patterns described by these authors. Confusion over

descriptions of Nephila courtship may arise, not

only because of observational problems but also

because, as we discovered, some stages of courtship

may be omitted by some males which behave in

an "opportunistic" manner. The significance of

"incomplete" courtship is discussed later. The best

case of this that we have documented is the one

where the male approached a female that was in

the process of molting to the adult stage, and mated

with her while she was still "drying out" and hanging from her cast skin. Approach in this case was

accomplished in less than one minute and insemmination was over shortly afterwards. We have the

entire sequence recorded on film. Crane (1949:176)

records a similar case in salticids; the female later

produced fertile eggs.

Other examples of opportunism include behavior

sequences where the male climbs onto the female

and copulates while she is feeding, and omits the

typical precopulatory behavior. We have two records of this type of mating and the absence of silk

on the body of the female confirmed that the "normal" precopulatory behavior had been omitted.

Figure 17 shows a male in the process of copulation

while the female is feeding, but in this case the

male had carried out the lengthy normal precopulatory behavior.

In all the other cases of courtship that we saw

the procedure was essentially the same, although

there were some differences of detail. We have never

seen the entire process from start to finish, but

have seen all the stages and filmed them on many

occasions. Essentially there are three fairly distinct

stages: approach and movement onto the female,

complex silk deposition on the female, and movement toward the cpigyne leading to copulation.

The approach stage may occur when the female

is at the hub, where she may or may not be feeding,

or it may occur at a prey capture site when the

female is attack-biting the prey. The male approaches the female on either side of the web, i.e.,

either from the upper surface "facing" the female

or along the lower surface on which she is standing.

If the male arrives at the female on the upper

surface he shuttles through the web to the side on

which she is located. Then follows a period of

touching which may vary in interval from a few

seconds to several minutes. At this time the male

may touch the tarsi of any of the female's legs

and/or her mouthparts and pedipalps. This phase

ends when the male climbs onto the female or retreats. Once on the female the second stage commences.

The second stage of laying down silk threads on

the female may occur intermittently for very long

periods and the male may spend the greater part of

several days standing on the female. During this

time he periodically indulges in complex "weaving"

or thread deposition activities. We have one record

of two hours continual activity at this stage, which

was the longest period of uninterrupted observation

that we carried out. To observe the details we

watched the pair through the lens system of a cine

camera equipped with a telephoto zoom lens, to

which we attached a supplementary close-up lens.

This allowed us to watch the pair from a distance,

and, at the same time, vary the field of vision from
NUMBER 149

FIGURE 17.—Profile view of copulation in Nephila maculata. One em bolus of the male is inserted

(A) . The gusset of silk that the male has attached from the abdomen of the female to her

thorax is dearly visible (B) . Silk can also be seen on the leg bases.
38

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

one occupied by the entire female to a narrow view

of only part of her body. Such observation is very

tiring and two hours was really beyond the limit.

The notes on this session are given in Appendix 1.

Essentially the male lays down silk threads between

the bases of the female's legs and between the

prosoma and the dorsal basal edge of the opisthosoraa. Nearly all of the bouts of silk deposition,

observed during the 2-hour session, were initiated

by the male moving down from dorsal surface of

the female's abdomen, where he had been standing

motionless. Before moving onto the thorax the

male attached silk to the raised fronto-dorsal edge

of the abdomen. The distinct dabbing movements

of the male spinnerets against the female marked

the start of a deposition bout. The male attached

silk lines between the abdominal edge and positions

on the dorsal surface of the prosoma. He returned

frequently to the abdomen to repeat the process.

Threads were placed on the opisthosoma at various

distances from the raised anterior edge of the

structure and then stretched to points on the prosoma at varying distances from the waist. They

were stretched parallel to the long axis of the

spider and also at angles such as left opisthosoma

to right prosoma. Mixed in between these movements were those involving the leg bases. In these

the male moved either from the opisthosoma, or,

more frequently, from the prosoma, onto the coxatrochanter region of one or other of the eight legs.

He then attached lines to the leg base immediately

beneath it. Attachments were made to the upper

and lower surfaces of the basal joints and from

these to leg bases on both adjacent and opposite

outsides of the prosoma. In the latter case the

lines traversed the dorsal surface of the prosoma.

The most interesting postures adopted during

this lashing process occurred when the male, from

above, passed lines onto the lower (ventral) surfaces of the legs. To do this the male would arch

his body and twist it sideways between the legs so

that it moved like a shuttle. On occasion the male

moved entirely beneath the leg bases while attaching threads. The results of this silk deposition can

be seen in Figures 17 and 18, which are of two different adult females. The view in Figure 17 shows the

lateral profile of the two spiders (male + female)

and, on the female, a sheet of silk threads can be

seen curving from the anterior edge of the opisthosoma to the posterio-dorsal region of the prosoma.

Also visible in this photograph is a complex of

threads extending well up onto the femur of left

leg n and other threads connecting the base of right

leg i to the basal region of the right chelicera.

Figure 18 is a dorsal view of a pair of Nephila and

shows silk lines between all the leg bases and also

the complex of threads on the dorsal surface of the

prosoma. Figure 19 shows another pair of spiders

with the male in the act of attaching silk to the

left lateral aspect of the female's opisthosoma.

Some lines are attached from the leg bases to the

ventro-lateral margins of the prosoma, but the male

spends very little time beneath the female during

the process of silk deposition.

During the process of intermittent silk deposition

the male rests fairly frequently. The rest attitude is

almost always assumed on the dorsal surface of the

female's abdomen and usually above the raised anterior edge (where there is a fairly conspicuous pale

line). While they are resting males may tap at the

bases of the female's legs, or hold onto these with

the feet of legs i and II. Contact in these cases may

possibly be with the silk between the leg bases of

the female. We have records of males assuming

special postures when the female moves about in

a precipitate manner (as she may do during a predatory excursion). One male consistently responded

to the movement of the female by flattening himself

against the steeply sloping anterior declivity of the

abdomen and in this position could be seen clinging

to the silk "shrouds" on the thorax. Such a position

was also adopted by other males for which we have

a less complete record. We are inclined to believe

that this is the most secure and sheltered position

that the male can adopt and that it may help to

secure him against disturbance by the female.

We saw few instances in which the female appeared to respond to the activity of the male.

These rare responses only occurred when the male

was on the ventral surface of the legs. In this situation several females made brushing movements

directed at the males (by bringing the tibia of a

third leg along the underside of their prosoma).

These movements were similar to those made in

apparent response to the activities of kleptoparasites. Copulation follows the stage of silk deposition, and approaches to the female genital orifice

may occur intermittently during silk deposition
NUMBER 149

FIGURE 18.—Male on dorsal surface of the abdomen of a temale Kephita maculata. Silk lines

are visible on the thorax of the female leading to the leg bases and abdomen.
40 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FICIRE 19.—Male Xephila maculata in the act of attaching silk to the right fourth leg of the

female. Silk produced by previous deposition activities is clearly visible on all leg bases. Note

that at least five kk-ptoparasitcs are visible on this photograph.
NUMBER 149 41

bouts. We have film records of three successful

copulations and a still photograph of another (Figure 17).

Approaches to the region of the epigyne are made

by two basic routes. The male most frequently

moves on the dorsal surface to the apex of the

opisthosoma and then walks forward down the

ventral surface, halting just behind the margin of

the epigyne. There is a tuft of longish stiff hairs

immediately anterior to this furrow and these may

act as a marker for locating the appropriate region.

The male can also circle around the anterior region

of the opisthosoma to reach the same point, and

frequently retreats from the ventral surface by a

rapid circling move. When descending the ventral

face of the female opisthosoma he is clearly belayed on the drag line which is attached somewhere

near the abdominal apex. Presumably the drag line

is also used when circling, but it is not then clearly

visible.

Copulation

A typical copulatory position is shown in Figure

17. From this it is obvious that only one embolus is

inserted at a time and the other is simultaneously

raised above the long axis of the male's body. The

swollen distal portion of the pedipalps are, at this

stage, black and shiny, the emboli are long and

extremely narrow in their distal region. The embolus of the left palpus is clearly visible in its

inserted position in the photograph. Insertion may

be very brief and is often a matter of seconds. Such

brief insertions may represent unsuccessful attempts. At other times they may last for over a

minute. The removal movements are conspicuous.

The structures sometime appear to stick so that

there is a distinct recoil upon the embolus being

freed. Insertion is preceded by the spider beating

upon the female genital region with very rapid

alternating movements of the pedipalps. Analysis

of film suggests that this beating is done with the

emboli reflexed backwards.

The palps are used alternately, several times,

with pauses between bouts of insertion. Bristowe

(1941:491) suggests that this technique is used by

the majority of spiders.

Charezieux (1961:377) shows a pair of Nephila

tnadagascariensis in a copulatory position exactly

comparable to that adopted by N. maculata. He

notes (1961:378) that the male beats on the epigyne

with his palps ("II frappe alors de ses bulbes copulateurs l'epigyne, les actionne rapidement tous les

deux"). He does not state whether one or two palps

are involved at the same time, although this may be

implied. Charezieux also refers to the brevity of

copulation and also to the fact that it may be

repeated several times.

The female makes no attempt to attack the male

during or after copulation (in marked contrast to

the behavior of several New Guinea Argiope species; Robinson and Robinson, in prep.). Thakur

and Tembe (1956:331) state that copulation occurs

at irregular intervals for a day or two, and that the

female does not attack the male, but that "he just

dies a natural death, apparently due to exhaustion."

They do not describe the act of copulation.

Discussion

The most interesting aspect of the courtship behavior of Nephila maculata is the complex thread

deposition, which the male normally undertakes.

This behavior was not described by Fischer (1910a,

b,c) Hingston (1922a,b,c, 1923) or Thakur and

Tembe (1956), although the latter authors presumably are referring to the results of this process

when they state that the male builds a web on the

back of the female (1956:331). Preliminary studies

that we have carried out on Nephila clavipes suggest

that silk binding is absent from the mating behavior of that species.

It is not described for N. madagascariensis, and

presumably would not have been missed by the

authors that studied this species. As far as we are

aware there are no published accounts of other

araneids indulging in such complex silk deposition

during courtship. Bristowe (1929:320-321), however, records that during the courtship of Meta

scgmentata the male may begin to wrap the female

as though she were prey. The female tears herself

free and Bristowe assumes that the behavior is the

result of multiple motivation and that although

the female is not restrained by the silk she may

be stimulated by the male's actions. Bristowe (1929)

and others following his generalizations based on a

limited number of observations on a limited number of species (e.g., Platnick 1971:40-41), state
42 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

that courtship in araneicls involves the building of

mating threads onto which the female is coaxed

during mating. Descriptions of the construction of

mating threads, e.g., by Meta segmentata (Bristowe,

1929:320-321), mention that the male walks backwards and forwards over the female trailing a

series of threads that are eventually to become a

single composite copulation thread (=mating

thread) on which copulation occurs. It is not clear

from the description exactly how the copulation

thread is oriented in relation to the female, whether it is dorsal or ventral. If it is laid down by the

male walking across the dorsal surface of the spider

then there is some similarity between this and the

behavior that we have detailed for Nephila maculate Our own observations on the mating behavior

of Argiope aemula show that the male moved very

extensively over the dorso-lateral surfaces of the

female piior to copulation (Robinson and Robinson, in prep.). These movements had some of the

character of the Nephila maculata binding movements but did not include discernible silk attachment movements. The existence of such wandering

may be of interest in considering the evolution of

courtship behavior in araneids. In passing it is

worth noting that in Thomisids the male may, as

in the case of Xysticus lanio C. L. Koch, tie the

female to the ground with silk. This process, described by Bristowe (1931:1406) is presumably not

entirely to restrain the female since she frees herself after copulation has occurred.

Perhaps the most interesting question about the

binding behavior is: what is its function? At first

sight it would seem logical to assume that it functions in some way to restrain the female so that the

male can safely copulate. This is suggested, albeit

indirectly, by the fact that the behavior is omitted

on occasions when the male can catch a female at

the molting stage or while she is feeding. Despite

the fact, however, that the leg bases are the subject

of a great deal of binding activity, the female is

well able to rush off on predatory excursions from

the hub after the silk has been heavily deposited.

Her running ability does not, therefore, seem to be

impaired. It may be that the binding, particularly

the deposition of threads from the opithosoma to

the prosoma, on the dorsal surface only, prevents

the female from bending at the waist. The male

would then be able to copulate without the danger

of being picked off by the female. This explanation

of the binding behavior only occurred to us after

we had seen Argiope aemula mate, and in the process pick off the male from her ventral surface. This

observation was made at the end of our stay in New

Guinea and we were not then able to carry out

any experiments on the efficacy of the binding in

preventing the Nephila female from moving at the

waist. However, we have since carried out experiments with the females of Nephila clavipes and

gluing threads on dead females effectively prevents

backward ventrally directed movements of the

prosoma. This evidence is certainly not critical but

is suggestive. The unrestrained spider is able to

bend at the waist to an angle of over 90 degrees

when not in contact with a substrate (presumably

by contracting muscles associated with the waist

joint) and further than this when it can use the

legs to pull the thorax towards the abdomen. It

can also achieve a more than 90 degree flexure by

allowing the abdomen to drop toward the thorax

in a ventral direction, a situation in which the

action of internal muscles is presumably supplemented by gravity. This degree of bending could be

sufficient to enable the female to pick off the male

in certain circumstances, i.e., by seizing one of the

legs projecting beyond the waist joint onto the

prosoma of the female. This can be visualized by

examining Figure 17.

If the act of mating were to be accomplished

rapidly, once the male had assumed a copulatory

position, there would not seem to be any adaptive

advantage in insuring his postcopulatory survival

by an elaborate precopulatory behavior pattern. If,

however, a binding function of silk deposition

insures that the male can safely achieve repeated

insemination bouts it could be of survival value.

The immunity of the male to attack by the

female, a point that we have observed in all the

matings that we have seen, could be a direct consequence of the binding behavior as suggested above

or it could be that the female is not restrained by

the silk but by some change in her internal state

consequent on the males' behavior. There are a

large number of cases of complex courtship patterns

which have the effect (among others) of lowering

hostility between the sexes or reducing predatory

drives that might otherwise be directed against the

male. In this particular case the restraint is not
NUMBER 149 43

exercised during the approach stage, which may

also be one during which the male is at risk, but

actually during the process of copulation. Signaling

systems may exist that enable the male to identify

himself as nonprey to the female during the approach stage. The web-strumming that the male of

Nephila madagascariensis performs during his approach (Charezieux, 1961) would seem to belong

to this category. We did not observe such behavior

in the case of Nephila maculata. (We suspect that

the males of N. maculata may be light enough not

to trigger a predatory response as they move across

the web.)

There are still other possible explanations, in

terms of function, of the complex binding behavior. The structure could be a sperm web. We

consider this unlikely because it is constructed in a

manner which suggests unnecessary complexity for

such a function. A sperm web would presumably

not need to encompass the leg bases in such a

thorough way, nor would the complex diagonal

members laid down from opisthosoma to prosoma

seem to be necessary. However, since we did not

observe sperm induction we cannot entirely exclude this possibility. A further possibility is that

the structure provides a foothold for the male so

that he can cling securely to the female until the

moment for copulation arrives. This too seems a

fairly remote possibility since the male could,

presumably, achieve a secure position on the female

by attaching his drag line to some part of her body

and gripping its far from smooth surface with his

tarsal claws. At the most he could achieve a very

secure foothold with a modest skeleton structure of

silk lines rather than the complex structure that he

does build.

The foothold theory gains no direct support from

our observations on Nephila clavipes. These show

that the male is able to move about the surface of

the female with facility for long periods, and remain there during fairly violent activity (during

prey wrapping) without a silken foothold structure.

A primary foothold function for the silk could

thus be justified only by assuming that the surface

of Nepliila maculata afforded considerably less foothold than that of Nephila clavipes.

There is no reason to assume that the silk structure has only one function. Therefore, it could

function as a restraining "harness," a platform of

footholds, and a sperm web.

All the authors who have described Nephila mating refer to the passivity of the female during

copulation. It seems worth reiterating that courtship activities may function principally to induce

such a state, which may be due to internal rather

than external restraint.

The proportion of matings that we observed in

which the stage of silk deposition was omitted do

not raise major problems in explanation. Behavioral investigation of courtship patterns over a

wide range of organisms has shown that stages in

a species-specific courtship pattern may be omitted

in a proportion of instances, while at the same

time successful mating ensues. Such exceptions are

often explained in terms of variations in individual

readiness to mate or reproductive drive, etc. Ethologists argue about the validity of drive concepts

(Hinde 1966:139-147), but accept the fact that

animals do not always respond to the same stimulus

situation in the same way. Morris (1956) shows

how courtship patterns that can be idealized into

reaction chains do, in reality, have a degree of

variability in both the presence of, and ordering

within, their component units of behavior. Thus

one explanation for the opportunistic males of

Nephila maculata (which copulate without first

going through the normal prior phase of silk deposition on the female) would be that they are highly

motivated to copulate and that this internal state

in some way suppresses the preliminary elements of

behavior. Alternatively males could be regarded as

capable of recognizing situations in which certain

stages of mating can be omitted as unnecessary.

Our observations do not provide any basis for deciding between these and other possible alternatives.

A further general problem remains. Alexander

and Ewer (1957:312) in their discussion on the

origin of mating behavior in spiders argue that the

"double process" of spider mating (stages of sperm

induction and sperm transfer) confers a selective

advantage in that "it permits the male to prepare

for the mating beforehand, and, when in the proximity of the female, to be as quick as possible

with the actual insemination." They postulate that

sperm induction may have evolved through an

intermediate stage of spermatophore production, as

in pseudoscorpions and scorpions, and that the pro-
44

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

tospiders may have produced spermatophores that

became redundant when web-spinning arose. To

our view, however probable this may be, it does

not bear on the problem raised by the mating

behavior of Nephila maculata, where although the

male may be prepared to insemination beforehand

he nevertheless spends a great deal of time actually

in contact with the female before copulation occurs.

PREDATORY BEHAVIOR

Behavior Units of Nephila maculata

In this section we describe the behavior units in

order, from those involved at the initiation of a

predatory excursion to those preceding the onset

of feeding at its successful conclusion.

BEHAVIOR PRIOR TO CONTACT WITH THE PREY.—

Predatory Position at the Hub: The normal waiting

position at the hub is shown in Figure 2. Note that

all the leg pairs are separate (compare with the

predatory position of Argiope argentata described

by Robinson and Olazarri, 1971:2) and extended in

a more or less bilaterally symmetrical pattern. Normally all the tarsi are in contact with web members,

but under the influence of strong incident sunlight

this position may be considerably modified (p. 64).

The spider rests on the underside of the web, at

the hub, with the body more-or-less parallel to the

plane of the web. The drag line is attached to the

web just above the hub. The waiting stance of all

the species of Nephila that we have seen is fundamentally similar, even to the disposition of the

legs and the angle that they form to the body.

Plucking-. After there has been an impact of some

object with the web the spider orients towards the

general direction of the prey (or other object) and

then may either approach directly or make plucking movements. These are usually carried out with

both legs i, which may be extended almost parallel

to each other in the direction of the prey (Figure

20). In effect the spider jerks the web members on

which the tarsi of legs i are placed, without breaking tarsal contact with the web. Such plucking

movements may be repeated as the spider approaches the prey across the web. As in the case of Argiope

argentata, plucking movements occur most commonly if the prey is immobile after it strikes the

web. Approach plucking may be abandoned and

the spider accelerate towards the prey if the latter

becomes active after a plucking bout. Radii lying

within a fairly wide sector around the prey may be

plucked before the spider leaves the hub on a predatory excursion. When this happens the spider

eventually approaches along the radial direction

leading to the prey. We have never seen the spider

have to make directional corrections to the left or

right after it has set out on an approach pathway

initiated by plucking. We have seen such corrections made when the spider has run towards the

prey without prior plucking. A full discussion of

the possible function (s) of plucking is given in

Robinson and Olazarri (1971:5-6) and their conclusions are supported by our observations on Nephila

maculata. This species often carries out widesector plucking after returning to the hub following

a predatory excursion. It will also perform plucking

movements from a prey capture site if other prey

become entangled nearby. Such prey may then be

approached without the spider first returning to the

hub. We have not seen Argiope species behave in

this way.

Approaches to the Prey: Approaches to prey may

be rapid or slow and deliberate. Rapid approaches

are made by the spider running across the undersurface of the web and occur most frequently when

the prey is active. In such cases the spider may even

overshoot the position of the prey along the radial

pathway by several inches (this occurred in 3 out

of 20 presentations of live dragonflies to adult female spiders). After overshooting, the spider either

turns or backs up to the prey. Approaches may

start slowly and accelerate if the prey becomes

active during the approach. Slow approaches may

be punctuated by pauses during which the spider

stops and plucks, or may be continuous, when

plucking with one leg i may form part of a stride

forwards.

Very large prey may be approached slowly even

when they are active. When the spider nears such

prey it may raise legs i and one or both legs II off

the web and flex them dorso-posteriorly. The resultant stance looks very defensive. It may also

involve a dorsally directed concave curvature of

the entire body brought about by flexion at the

waist. A similar posture was noted by Robinson and

Mirick (1971:128) in the case of Nephila clavipes.

A very similar posture is adopted if the spider is

touched lightly from above when it is at the hub.
NUMBER 149 45

FICURE 20.—Female Nephila mmculaU plucking as the advances toward prey (not shown).
46

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

All approaches to prey involve the production of a

dragline by which the spider remains attached to

the web at some point. The spider at the hub has

a dragline attachment to the web at the hub region,

but it frequently reattaches the dragline before

making a predatory excursion. It seldom attaches

the dragline at other points on the approach pathway. Exceptions to this occur when the prey is

particularly heavy, then the spider can be seen to

make the characteristic dabbing movements of the

spinnerets against the web, as it closes with the prey.

Not all objects striking the web are approached

and particularly heavy objects may elicit an escape

response. In the escape response the spider runs

up from the hub to the upper frame members, towards nearby vegetation. Escape responses are

described in detail later.

BEHAVIOR ON CONTACT WITH PREY.—Touching

and Palpation: In most cases when the spider contacts the prey it touches the prey with one, or both,

legs i and continues its approach until it is standing with the anterior prosoma above part of the

prey body. The tarsi of the leading legs touch the

prey and the approach gait is unbroken until the

spider assumes the attack stance. However, in

some cases, when the prey is touched with the tarsi

of the outstretched leading leg(s) the spider halts

so that it is approximately a leg i length away from

the prey (8-9 cm). It may then back up the web

until it is more than this distance from the prey,

and wait out of contact, or even retreat to the

hub. We saw such behavior only in the case of very

heavy prey (over 1.5 grams) and then only in a proportion of cases. When halted the spider may

raise legs i and II off the web and assume the peculiarly curved attitude described above. Eventually

the spider either retreats to the hub (infrequently)

or advances slightly and taps the surface of the

prey with the tarsi of legs i. The tapping movements, are slow, deliberate, and often repeated.

Verbatim notes of attacks on large acridiids in

which bouts of tapping occurred are reproduced

in Appendix 2.

Tapping is often followed by prolonged tarsal

touching and then most frequently by the bite and

back-off attack behavior described below. However,

in a proportion of cases, touching is followed by a

slow advance to the assumption of an attack stance

over the prey and in this case, as the spider moves

forward, the pedipalps may be extended and contact the prey during the advance. In some cases

they may be lowered onto the surface of the prey

only when the spider assumes its attack stance. This

pedipalpal contact (=palpation) is almost certainly

made during the normal touching approach but is

not then conspicuous because the advance to an

attack posture merges without pause into attack

itself and a separate palpation stage cannot be distinguished. Exceptions to this have been observed

in attacks on pentatomids and reduviids when

there is sometimes a pause between the assumption

of an attack stance and attack. We presume that the

odors produced by these insects may affect the

spider and contribute to the abnormal pause that

allows palpation to be seen as a distinct stage.

Robinson (1969) found that Argiope argentata

palpated prey that were covered in spider silk in a

very distinct way and assumed that they did this

because they received an unusual stimulus from

such prey.

ATTACK BEHAVIOR.—Nephila maculata attacks all

prey with the jaws and does not use silk as an

attack weapon. Three types of attack are discernible.

Long Bite: The greater proportion of prey is

dealt with by a sustained or long bite. The spider

opens the chelicerae (by lateral movement), stoops

and inserts the fangs into the prey. The bite is

then sustained at its initial point of entry for a

long period. If the spider is dealing with a prey

that is vibrating or kicking, the point of insertion

of the fangs may be the point of initial contact

and therefore apparently random in location. Sometimes this bite may be ineffectual, as for instance

when the spider bites into the wing of a moth and

the fangs simply pass through the structure. Such

bites are corrected and the spider moves the point

of insertion, in steps, until it contacts more substantial tissues. Stepwise movements of the point

of insertion of the fangs may occur in bites that are

initially delivered to the body of the prey, and

these are more difficult to account for in terms of

function and causation. Thus in 12 out of 25

encounters with live dragonflies the bite was eventually sustained at a point on the thorax just behind the head. Since bites were moved to this

position from other locations in 6 of the 12 cases

there could be some element of choice in the exact
NUMBER 149 47

location of the bite on the body of the prey. (This

region of the prey plus the thorax in general may

be a particularly conspicuous target in contrast to

the abdomen which is long and very narrow.)

The spider could presumably determine the

location of this target at the touching stage. In

addition, the wings are attached to the bulbous

thorax and vibrations of the web produced by

wing movements could lead the spider to this region. (Four bites were initially aimed at the wing

bases). Hingston (1922c:920) states that N. maculata always bites the thorax of the prey first; thus,

"she behaves as though she knew the anatomy of her

prey." Bites at some heavily sclerotised insects may

not penetrate at first attempt and the spider may

move along the prey, attempting an insertion, until

a vulnerable region is found. In presentations of

inelolonthid beetles we found that the spiders appeared to be unable to penetrate the smooth and

curved elytra. Sustained bites at these beetles were

often made at the lateral or apical margins of the

elytra where the soft ventral surface of the abdomen

apparently offered a more easily penetrable bite

site. Attempts to bite into the elytra were made

and the impact of the fangs as they repeatedly

glanced off the cuticle could be heard distinctly.

Bite and Back-off'. As described earlier, and by

Robinson and Mirick (1971) in the case of Nephila

clavipes, attacks that are preceded by slow approaches and made after leg raising and preliminary tapping of the prey are often carried out by

the bite and back-off behavior. This entails a rapid

lunge at the prey followed by a short bite and subsequent retreat. After the first bite the spider retreats to a position usually within about 10 cm of

the prey. Lunges, bites, and retreats may be repeated a number of times. We have a record of 9

cycles of attack over a period of 80 seconds when

the prey was a large melolonthid beetle and one

of 13 such attacks, in 2 bouts, for an attack on a

5 cm acridiid. The bites are rarely sustained for

more than a few seconds. We suspect that they seldom exceed 5 seconds, and most of them are considerably less. They are usually carried out with

legs i and II raised back over the prosoma of the

body of the spider and the spider's body arched.

Prior to the attack there are often intention movements, during which the spider spreads the jaws

to a pincer-like extent while swaying forwards

and then backwards on the spot where it is standing.

After a series of attacks the spider moves close to

the prey and delivers a sustained bite. This may be

preceded by tapping and palpation. We have seen

a series of short bites followed by wrapping behavior without the occurrence of a sustained bite.

Even a sustained bite may be interrupted by the

prey struggling vigorously.

Seize and Pull-out: Very small and light prey are

simply seized in the jaws and pulled from the web.

Thus in the presentation of 50 live blowflies (25-50

mg) the bite time was one second or less in 4 cases

and this was followed by a pull-out time of similar

duration. On a purely arbitrary basis we can

separate this behavior from the other attacks on

these flies where bite times of up to 18 seconds were

recorded (average for all 50 attacks 5.16 seconds).

The distinction between a short bite and seizure in

the jaws is thus somewhat arbitrary. A less arbitrary

criterion for distinguishing between the categories

"seize in jaws" and "bite" would be possible if it

could be determined whether venom was used

when the prey was simply seized in the jaws and

pulled from the web. The distinction between seizure in the jaws and biting in Argiope and other

advanced araneids is made operationally and is

simple, since prey that are bitten are always wrapped at the capture site. This is not the case with

Nephila species since prey that are given sustained

bites of several minutes may subsequently be removed from the web by being pulled out (Robinson, Mirick, and Turner, 1969; Robinson and Mirick, 1971).

REMOVAL OF PREY FROM CAPTURE SITE.—Pulling

Out: At the termination of a biting attack the

spider almost always attempts to pull the prey from

the web. This behavior occurs in all the Nephila

species that we have observed and Robinson and

Mirick (1971; 129) have described it in the case

of Nephila clavipes. Hingston (1922c:920) describes

this behavior as tearing the prey from the viscid

attachments. Without releasing its cheliceral hold

(i.e., bite) the spider pulls outwards on the prey,

often repeatedly flexing and extending its legs in

the process. If the prey becomes freed it is then

carried back from the capture site to the hub. Sometimes if it becomes only partly freed, the spider

may hang away from the web wholly or partially

suspended on its drag line and pass its legs between
48

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

the prey and the web. This motion frees the prey

of the remaining attachments essentially by stripping the viscid element away from the prey in a

"teasing" movement. Damage to the web resulting

from the process is surprisingly slight. In most

cases, a few viscid spiral elements may be broken

and the golden droplets of adhesive stripped off

others, but large holes are rarely produced. This

contrasts sharply with the results of the cuttingout behavior carried out on prey that are wrapped

at the capture site.

(Records of prey capture sequences given in the

next major section of the description of predatory

behavior show that the pull-out technique succeeds

with certain types of prey. With other types of prey

it is either replaced, after failure, or, omitted

altogether.)

Wrap in situ: Very large prey, as well as prey

that for other reasons cannot be freed by pulling,

are wrapped at the capture site while still enmeshed

in the web. Such prey are cut from the web, partly

during the wrapping process and partly when it is

complete. Nephila species wrap relatively slowly

(when compared with species of the genera Argiope, Araneus, Eriophora, and others). The spider

stands on the prey and casts skeins of silk onto it

by alternate movements of the hind limbs. These

movements are easily counted, unlike the very

rapid movements of Argiope species. The prey becomes covered with a complex of silk skeins but

not completely enswathed in a layer of silk (another

contrast with the advanced spiders). The prey is

not normally rotated about an axis while silk is

laid down directly from the spinnerets, a behavior

frequently performed by Argiope argentata.

The wrapping bout is interrupted frequently as

the spider cuts entangling web elements that resist the passage of the wrapping silk over its surface. Cutting is done by bringing the chelicerae

down to the strand or by pulling the silk up to the

jaws on the tarsus of a leg, and also by apparently

snapping it with a foot. Towards the end of a

wrapping bout the spider may have turned through

180 degrees and be hanging with its dorsal surface

partly oriented towards the web, while the prey

is suspended below the web on just one point of

attachment. Figure 21 shows this remarkable wrapping stance. The consequence of this style of wrapping is that the resultant prey package invariably

hangs below the web. Attack wrapping by many

other species of araneid, on the contrary, often results in a prey package that lies securely in the

web plane and has to be cut out of the web before

transportation (Robinson and Olazarri, 1971, figs.

3,7).

Free-wrapping: As in the case of Nephila clavipes

(Robinson and Mirick, 1971:135-136) some prey

that are freed from the web by pulling are wrapped

before transportation. This form of wrapping results in the prey being trussed into a large fairly

compact prey package and is applied to bulky prey

that can nevertheless be freed from the web without being wrapped in situ. The freed prey may be

held in the jaws until the first skeins of silk are

passed over it by movements of legs iv; it is then

held with legs in until it is trussed in silk. The

spider is normally hanging below the web plane

while it performs the free-wrapping, in the manner

shown in Figure 21.

TRANSPORTATION TO THE HUB.—Carrying in Jaws:

Light prey are carried to the hub in the jaws, as

is the case with most araneids. Nephila maculata

commonly exhibits a behavior that we have only

seen occasionally in other Nephila species, and have

not noted in other araneids. Prey from the large

area beneath the hub of the web are carried in the

jaws as the spider backs up the web hanging head

downwards. This backing movement is illustrated

in Figure 22. In effect the spider fends itself off

the web surface with walking movements of legs

i, II, and HI while climbing "hand over hand" up

the drag line with the tarsi of legs rv. In cases where

we were able to watch the process at close range, it

became obvious that the spider was in fact gathering up quite considerable lengths of the drag line

into a loose hank as it made its ascent backwards.

The process is fairly slow compared with merely

turning and walking forwards to the hub. This

latter behavior does occur in the spider's repertoire

and ensures a more speedy resumption of its predatory position at the hub. Thus in 50 presentations

of live moths 42 spiders backed up the web, and 7

turned and walked or ran back to the hub. These

seven averaged 4.4 seconds for the return journey,

whereas the average time for those that backed up

the web was 34.8 seconds (detailed analysis in section on behavior sequences). What are the possible

adaptive advantages of this behavior? A spider
NUMBER 149 49

FIGURE 21.—Wrapping posture of Nephila maculata (based on film records)
50 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 22.—Nephila maculata backing up the web to hub.

Prey (carried in jaws) omitted for clarity. Note that the

dragline is being ascended backwards and collected in the

tarsus of the left fourth leg. (Based on successive frames of

film records).

carrying a load in its jaws and ascending the undersurface of an inclined web has the center of gravity

in a position that is more favorable to a troublefree ascent than a spider walking forwards with prey

in its jaws. The question of why N. maculata

ascends backwards and N. clavipes (for instance)

does not is difficult to resolve.

Carrying on Silk: The other basic method of

carrying prey back to the hub is on a silk thread

suspended from the spinnerets. The suspensory

thread may be suported by being held by one or

both legs iv, or may, less commonly, be without

secondary support. Large prey are carried back to

the hub in this way. Because of the slope of the

web, prey carried on silk hang away from the web

plane and seldom become entangled in the web

during transportation.

Wrapping in Transit: Prey, particularly those

carried forwards in the jaws, occasionally become

entangled in the web during transportation. When

this happens the spider makes pulling movements,

and, if these fail, briefly wraps the prey and then

proceeds to carry on silk as described above.

BEHAVIOR AT THE HUB WITH PREY.—Carried in

Jaws: Prey carried in jaws are almost always wrapped in silk on arrival at the hub. The spider usually

wraps in a head-up position comparable to that

shown in Figure 21, and turns to achieve this

position if it arrives at the hub in a different orientation. Before wrapping, the spider usually attaches

its drag line to the hub silk. Wrapping at the hub

is carried out in the slow manner that it characteristic of the genus. Small prey, carried from the upper

region of the web, are often wrapped when the

spider is in a head-down position (as it will be

when arriving from above the hub). Wrapping in

this case is achieved by the spider swinging the

abdomen into an almost horizontal position with

the anterior prosoma close to the web and the

apex of the opisthosoma well away from the web.

In this position the long legs rv can make wrapping

movements without fouling the web.

Carried on Silk: When the spider arrives at the

hub with prey suspended behind it on a silk thread

a process of attaching this thread to the hub region

is carried out. The spider dabs the spinnerets

against the hub silk at the point of arrival, thereby

making the first attachment of the prey to the hub.

It then turns until it assumes the head-down position normally adopted when the spider is at the

hub. As it circles to the left or right it attaches its

drag line, at intervals, to the hub. As it does this

the leg iv on the side opposite the direction of turning is used to stretch the drag line between the

points of attachment (Figure 23). The stretching

movement is essentially similar to the one that

most araneids use when laying down the viscid

spiral between the radii during web building. We

recorded the direction of turns made by spiders

during this rundgang and the number of attachment points made with different types of prey.
NUMBER 149 51

FIGURE 23.—Silk attachment during the rundgang. The silk

line leading from the prey package has been attached at

A, B, c. Between attachments, as between c and D, the spider

stretches the silk with movements of the appropriate leg

iv, as shown.

These data are given in the section on behavior

sequences.

Prey at the Hub: If the spider was feeding at

the hub before catching the prey with which it is

returning there is some modification of the behaviors described above. If the previous prey was

large the new prey will almost always be attached

at some distance from the old, often above it, and

the spider will resume feeding on the old prey

after the process of attachment. If the previous

prey was small, and/or partially consumed, the new

prey and the old prey are frequently wrapped together into one bundle and the spider then feeds

on the compound package.

Assumption of a Feeding Posture: After the

spider has suspended the prey package from the

hub it frequently backs a few centimeters up the

web and reattaches its drag line before moving back

to the central region of the hub. Before commencing

feeding the spider may undertake grooming activities in which the legs are rubbed together and particular attention given to the tarsal regions. The

tarsi of legs i and n are almost always drawn

through the chelicerae, one by one, after a predatory sequence, and the other tarsi may also be

treated in this way. After such grooming, and

sometimes a variable period of inactivity, the

spider often plucks the radii over a wide sector

and then reaches out with one of the first legs until

it contacts the thread on which the prey is suspended. It hauls on this thread until it can grasp

the prey package and manipulate it. The period

of prey package manipulation varies considerably

in duration and involves some or all of the first

three pairs of legs. The short third legs are used

for manipulation beneath the spider while the

flexed legs I and n operate in front of the prosoma.

During the manipulation the prey package is

moved backwards and forwards, rolled over and

twisted from side to side. The spider makes short

bites at the prey as it is manipulated. Eventually

the spider sustains a cheliceral insertion at one

point and places legs i and n back on the web in

their normal extended positions; one or both legs

HI may still hold the prey, but this is unusual. At

this stage we assume that the spider is feeding.

Feeding Behavior: We have not watched the

entire process of feeding, but examination of discarded prey remains allow certain deductions to be

made about the processes involved. The remains of

heavily sclerotized prey items, such as beetles, consist of entire exoskeletal shells. These suggest

straightforward suctorial feeding; however, the

elytra and membranous wings of beetles are often

found separately. We believe that these may be

nipped off and discarded during the feeding process. The discarded remains of orthopterans are

frequently in a highly comminuted state suggesting

that at some stage in the feeding process the

spider chews up the prey into smaller portions.

This process may facilitate the digestion of prey

material that is otherwise not readily accessible

to enzymes that are simply pumped into the interior

of a perforated but entire insect. Very soft insects,

such as flies, can be seen to be kneeded between
52 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

the chelicerae during feeding, and are highly compressed when dropped as trash parcels.

Behavior Units of Other Species

In Ghana, mainly in the Legon area, we encountered two species of Nephila: Nephila constricta

and Nephila turneri (the latter a large and striking

spider), as well as Nephilengys cruentata. We presented a variety of prey items to the Nephila species,

and also to Nephilengys cruentata. We concentrated attention on the latter species since the spider is

in many ways similar in appearance to an Argiope

and builds a cocoon-like retreat that is continuous

with the web. We encountered Nephilengys again

in Madagascar, at a forest site near Perinet and

carried out further observations there. We first

encountered Herrenia species at Manaas in Assam

and later encountered the genus at Periyar in

Kerala, South India. The spider builds elongate

webs close to large tree boles and from this habit

and its appearance we decided that it must be a

Nephilengys. We eventually found very similar

spiders building webs in similar situations at Wau.

Specimens of these were identified by Fr. Chrysanthus as Herrenia ornatissima. Since this genus is in

the Nephila group we carried out studies of its

predatory behavior.

All the Nephila group spiders that we studied

en route to New Guinea possessed broadly similar

behavior units. All attacked a wide range of prey

by biting. All except Herrenia ornatissima made

pull-out attempts after biting and all tapped large

prey from a distance before biting. The Nephila

and Nephilengys species showed the type of bite

and back-off attack on large prey that we have

described above for Nephila maculata. We were unable to induce Herrenia ornatissima to attack very

large prey and did not see bite-and-back-off behavior in this case. None of the spiders could be

induced to attack prey by wrapping, although we

presented types of prey (acridiids, beetles, dragonflies etc.) that Argiope species consistently attack

in that way. We observed wrapping at the capture

site (after biting) in all the species, and this was

performed with slow alternate movements of legs

iv as in Nephila maculata. All the species, except

Herrenia ornatissima wrapped prey, on occasion,

that had been freed from the web by pulling. All

the species hung prey at the hub and did not store

it at the capture site. Nephilengys cruentata assumed an extraordinary position in its retreat (Figure

24) facing outwards towards the web, but with its

dorsal surface towards the web that lies above the

retreat. Spiders returning to the retreat with prey

enter the retreat head first and turn over and towards the entrance when they are inside or at the

entrance. This considerably complicates the behavior of wrapping prey at the feeding site (hub or

retreat) and also complicates the process of hanging

prey at the retreat entrance (equivalent to hanging

it at the hub in the other species).

FIGURE 24.—Relationship of the retreat of Nephilengys cruentata to the main orb and the position of legs iv in relation to

the retreat. Note that these legs contact the dorsal surface of

the retreat which is continuous with the web surface.

Herrenia ornatissima builds its elongate webs

close to tree boles, often less than 2 cm away from

the bark, and rests in a cuplike silken depression at

the top of the web, close to or touching the bark.

This again poses problems since at this place the

spider only has access to the upper surface of the

web. It is interesting to note that the dorsal surface of this spider is beautifully camouflaged and

that it is very difficult to pick out against a background of bark (Figure 25). The specific name may
NUMBER 149 55

FIGURE 25.—Male (above) and female (feeding) Htrrenia omatissima on surface of web. The

web is built very dose to the surface of a tree and is elongate. The female has a camouflaged

dorsal surface.
54 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

be derived from the very bright orange-red spot

on the ventral surface that is not visible when the

spider moves about the upper surface of the web,

as it normally does.

We did not observe, in the other species of

Nephila, the process of backing up the web with

prey in the jaws that is so characteristic of the

carry-in-jaws technique of Nephila maculate.

Table 8 summarizes the main features of the

behavior units of these species.

TABLE 8.—Units of predatory behavior

(+ present, - absent, ? not known)

Behavior unit

Legs reflexed approach

Tapping

Bite and back off

Attack bite

Attack bite with leg raising..

Pull out

Wrap in situ

Cut out

Free wrap

Attack wrap

Carry in jaws

Carry on silk

Wrap in transit

Wrap at hub

Wrap at retreat

Leave prey in situ

I i

i 1

5 s

+

+

+

+

+

+

+

+

+

+

+

+

rare

+

?

that figure prominently in the diet of the Wau

spiders (p. 18) and others of interest for comparative purposes (Table 9).

TABLE 9.—Behavior sequences given by N. maculata to four types of prey (durations in seconds)

PREY WEIGHT (mg)

m

id

ATTACX UNITS

Bite

m

sd

Pull out

m

sd

Wrap and cut out

m

sd

TRANSPORT UNITS

Carry in jaws

Forward

m

sd

Back-up

m

sd

Wrap at hub

m

sd

Total

m

sd

*New Guinea. • Panama. * Ghana and Ivory Coast. ' Ghana

and Madagascar. * New Guinea and India.

Flies Moths Katydids Dragonflies

N=50) (N=50) (N=50) (N = 30)

34.8 137.3 129.6 110.9

11.2 56.3 30.3 21.2

5.1 15.8 16.6 44.5

3.8 9.5 10.0 31.6

2.5 16.4 16.2 52.2

2.1 13.9 17.2 24.2

lone none* none (N=21)

101.2

38.6

(N=7) (N=8) (N=S) On silk

(N=23)

102 4.4 4.0 23.6

9.3 1.9 - 11.5

(N=43) (N=42) (N=47) (N=7)

58.7 34.8 42.8 30.7

20.3 22.7 18.4 17.5

(N=6) (N=S5) (N=7)

.26.3 44.0 615 61.5

10.1 15.0 19.7 11.6

65.0

29.1

105.3

43.9

166.6

45.2

238.8

61.5

* One free wrap, one wrap in transit.

m = mean, sd=standard deviation.

Behavior Sequences

We follow Robinson and Olazarri (1971) in here

presenting descriptions of the behavior sequences

given to various types of prey. The responses given

to each type of prey are outlined separately and

illustrated in a standard form. Comparisons between the types of sequences given to different

types of prey are largely confined to the concluding

part of this section.

The prey types chosen for replicated presentations to the free-living adult spiders represent prey

Sequences with Live Flies: Fifty blowflies were

presented to SO spiders. Where the same spider was

used for two observations at least one day intervened between presentations. The results are summarized in Figure 26. All the flies were bitten for

short periods, pulled from the web and carried in

the jaws to the hub. On 7 out of 50 occasions the

spider turned at the capture site and ran or walked

back to the hub facing the direction of movement.

In all the other cases the spider backed up the web

in the manner described earlier. Only 6 of the 50

captured flies were wrapped immediately on arrival
NUMBER 149 55

at the hub. Only four spiders plucked the web

before rushing down to attack the prey—a reflection

of the fact that the majority of flies vibrated in

a sustained manner after striking the web.

FIGURE 26 Predatory sequences upon live flies. The width

of the arrows is proportional to the number of responses in

the direction indicated.

Five spiders overshot the mark, running beyond

the prey, as they made their attack. This led to

some delay in biting. The sequences are simple and

rapid; run to prey, bite, pull out, carry in jaws

backing up the web, feed.

Temporal Aspects: The attack and removal from

the web stages of the sequence are of short duration

(bite average 5.1 seconds, range 1-18 seconds; pullout average 2.5 seconds, range 1-13 seconds). The

total durations are long, due to the slow nature of

the backing-up process when the prey is carried in

the jaws. The average back-up time was 58.7 seconds, range 21-106 seconds, while the average turnand-run time was 7 seconds, range 3-13 (or 10.2

seconds if the one spider that turned and walked

to the hub is considered in addition).

The total sequence durations for those sequences

in which the spider turned before returning to the

hub are all less than two-thirds of a minute, the

others average well over one minute.

Sequences with Live Moths: Fifty live moths were

presented to 28 spiders. The moths were of different species but fairly similar in size and weight. All

were bitten at the capture site and then pulled from

the web, without capture-site wrapping. Eighteen

spiders plucked the web from the hub before making a predatory excursion. Four spiders had distinct

stages of touching or palpating the prey before

biting. Transportation was predominantly effected

by backing up the web with the prey in the jaws

(42 out of 50), seven spiders turned and ran back

to the hub with the prey in their jaws. One spider

wrapped the prey after it stuck in the web during

in-jaws transportation.

Fifteen prey items were not wrapped at the hub

after transportation, two of these had been wrapped

prior to or during transportation (1 free-wrap).

The form of the behavior sequences given to live

moths is summarized in Figure 27.

Temporal Aspects: The attack and pull-out

phases are of longer duration than in the equivalent stages of the attack on flies. Bites averaged

15.8 seconds; range 6-58 seconds, and pull-out units

averaged 16.4 seconds, range 1-70 seconds. Transportation times were again high in the case of

spiders that carried the prey in their jaws while

backing up the web (average 34.8 seconds, range

3-118). Those that turned and ran back to the hub

averaged 4.4 seconds; range 2-8. After wrapping,
56 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

CUT OUT

FIGURE 27.—Predatory sequences upon live moths.

15 spiders turned right at the hub and 20 turned

left. Wrap at hub averaged 26 leg movements per

spider and 2.1 silk attachments in the rundgang.

Wrapping at the hub after transportation (70%

of all cases) accounted for an average of 44.0

seconds.

Sequences with Live Katydids: Fifty live katydids were presented to 32 adult spiders. These were

bitten and pulled out in all cases. All except three

of the katydids were subjected to being carried in

the jaws as the spider backed up the web to the

hub. Three katydids were carried by the spider in

the jaws as it ran to the hub after turning at the

capture site. All the spiders wrapped the prey at the

hub after transportation. The sequence for small

katydids was thus very simple, as shown in Figure

28. Plucking occurred in 11 cases out of 50. It is

interesting to note that free-wrapping did not occur

in any of these sequences and that prey were not

wrapped at the capture site.

Temporal Aspects: Bite durations were slightly

longer than those given to moths, averaging 16.6

seconds. This difference is not significant (statistical

analysis in Table 9). The pull-out time averaged

16.2 seconds, slightly less than that given to moths.

Transportation times were high—mean 42.8 seconds—for those spiders that backed up the web with

prey in their jaws. The three spiders that turned

and ran back to the hub averaged 4 seconds for

transportation. All the prey were wrapped at the

hub after transportation and this behavior unit

accounted for a mean time of 61.2 seconds. Total

sequence durations averaged 166.6 seconds; this is

higher than in the case of moths. Thirty-three

spiders turned left at the hub and 17 turned right.

Silk attachments during the rundgang averaged 3.3

and leg movements during wrap at hub averaged

43.8 per spider.

Sequences with Live Dragonflies: The sequences

given to live dragonflies were characterized by the

high proportion of wrap and cut-out units that

occurred. Dragonflies are much more bulky than

katydids in the sense that a greater area of insect

structure become enmeshed and adherent to the

web, because of the body length and the extended

wings. At the same time the insects do not pull

easily from the web. This contrasts with moths

which have a large wing area in contact with the

viscid spiral. We therefore interpret the high proportion of wrapping at the capture site, which

occurs after extensive pulling-out attempts, as a

response to the problem of prey removal (Robinson

and Mirick, 1971). Twenty-one out of 30 dragonflies

were wrapped at the capture site after pulling-out

attempts. Pulling-out attempts were successful in

removing prey from the web in only nine cases.

Free-wrapping behavior occurred after successful
NUMBER 149 57

MTf

PUU OUT

f m -WHAP j CARRY

WRAP

AT

HIM

MAN»UtATt

FIGURE 28.—Predatory sequences upon live katydids.

pull-out attempts in one case and after cutting out

in two cases. Pulling-out movements resulted in the

spider severing the head of the dragonfly in one

case. The head was then transported to the hub

as though it were the entire prey. The spider removed and transported the remainder of the

dragonfly several hours later. Wrapping occurred

during transportation in one case. There were thus

four cases of wrapping not obviously associated

with the removal of the prey from the web or its

storage at the hub (three cases of wrapping at the

capture site after removal from the web and one

wrap in transit). Wrapping at the hub occurred

in every case where the spider freed the prey by

pulling, i.e., in all those cases where the prey was

carried to the hub without having undergone

wrapping behavior. Transportation was predominantly carried out by the spider suspending the

prey on silk behind its body and walking forwards

back to the hub. Twenty-three spiders carried

prey in this way although one of these started by

backing up the web with the prey in its jaws. The

prey in this case became entangled in the web,

was wrapped in situ, cut out, and then carried on

silk. Figure 29 summaiizes the results.

Temporal Aspects: Bite durations averaged 44.5

seconds, persistant pull-out attempts after biting

averaged 52.2 seconds (only nine of these were successful). Wrapping at the capture site averaged

101.2 seconds in duration. Total sequence time for

live dragonflies averaged 238.8 seconds. This mean

sequence time is higher than that involved in any

of the sequences reviewed so far despite the fact

that the dragonflies were not heavier, on average,

than the moths or katydids (Table 9). The seven

spiders that wrapped at the hub averaged 61.5

seconds for this behavior, four turned left and three

turned right.

Sequences with Large Acridiids: We made 25

presentations of very large acridiids to an equal

number of spiders. These insects were between ca.

45 mm and 50 mm in length and between 2 and 3

grams in weight. They had large mandibles and

spiny posterior legs. They thus were potentially

dangerous and capable of vigorous escape and defense activities. We expected that they would present considerable problems to a spider that did not

have an attack-wrapping behavior. They did. The

spiders were successful in completing a predatory

sequence in 13 out of the 25 cases. Twelve acridiids

escaped at some stage in the spider's attack sequence or without being attacked. The successful

sequences were all highly complex and the partial

sequences of the unsuccessful spiders that attacked

the grasshoppers were also complex. The complex
58 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 29.—Predatory sequences upon live dragonflies.

sequences cannot be given in diagrammatic form but

a selection of verbatim field notes are given in the

appendix. In general the sequences showed complexity at the approach, attack, and removal from

the web stages. Approach was of the hesitant type

described in the section on behavior units. In more

than half the cases approach was preceded by retreat from the hub away from the point of impact

of the prey. This form of defensive behavior makes

adaptive sense when objects hitting the web are

large and/or heavy. Attack units involved the

employment of the bite-and-back-off technique with

numerous repetitions of the short bite. Retreating

away from the prey between bites was a fairly regular occurrence. Early bites were often directed

at appendages rather than the body proper and this

again indicates the temerity with which the spider

approaches such large prey. Prey removal always

involved extensive wrapping even when the degree

of attachment to the web had been greatly reduced

by the tearing consequent on the prey's struggles.

A summary of the major features of the complex

sequences is given below.

Temporal Aspects: Because of the repetition of

major units in the attack and approach systems, as

well as extensive prey-packaging operations, the

duration of the total sequences is consistently high.

In extreme cases the duration exceeds three-quarters of an hour. The data (below) on both structural and temporal aspects of the sequences support

the analysis given above.

UNITS OCCURRING IN THE 13 SUCCESSFUL

SEQUENCES

Sequential order of units Proportion of occurrence

1. Retreat from hub before attack 9/13

2. Plucking before attack 7/13

3. Slow approach ± leg raising 11/13

4. Tapping prey before attack 8/13

5. Bite and back-off attack 11/13*

6. Sustained bite ± prior 5 12/13

7. Wrap in situ, interrupted by rest periods 13/13

8. Carry on silk 13/13

9. Hang on hub 13/13

• Maximum numbei of interrupted bites = 13 in two

sessions, 3 followed by 10, more than 8 minutes later.

DURATIONS (MINIMA AND MAXIMA) FOR THE 13

SEQUENCES (in minutes and seconds)

Sequential order of units Range

1. Approach (from retreat position or hub) 1:10-7:40

2. Bite and back off 0:54-14:10

3. Sustained bite 0:40- 8:30

4. Wrap and cut out 1:14-13:40

5. Transportation 0.30- 3:10

Total Sequence Time:# 9:40-47:01

• Includes time spent retreating and rest periods, which are

not included in units 1-5.

Sequences with Live Melolonthids: At certain

times of the year melolonthid beetles constitute an
NUMBER 149 59

important element of the prey captured by freeliving spiders. Initial observations suggested that

these bulky, comparatively heavily-armored insects,

are not easily subdued by the biting attacks of

Nephila maculata. We, therefore, presented living

melolonthids to the spiders and concurrently presented a similar number to the much smaller

Argiope aemula. The latter species builds its webs

in the herb layer and is much less likely to catch

the beetle in large numbers. It is, however, a spider

that has attack wrapping as its major predatory

strategy and a comparison of the behavior of the

two species towards the beetles was of interest. For

ease of comparison we include details of the Argiope predatory sequences in this section, under a

separate heading.

Ten melolonthids were presented to both species

of spider. Nephila maculata attacked, in all cases,

by biting attacks, but these proved to be more

complex than any that we had previously observed

in that they did not conform to the "typical"

pattern. Thus the bite-and-back-off pattern was

employed in five out of ten presentations but in

only one case was it followed by a sustained bite.

In four out of the five cases the spider wrapped the

prey after a series of bite-and-back-off units. This is

most unusual. In the five other presentations the

spiders made bites at the prey without withdrawing

from contact between bites, but in only two cases

were a series of such bites followed by a sustained

bite; in the three others the spider then proceeded

to wrap the beetle. Thus contrary to the pattern

observed in presentations of other insects, wrapping

occurred in the absence of a sustained bite in all

but three of the cases. Examination of the detailed

notes on the sequences shows that the spiders had

extreme difficulty in penetrating the hard, smooth

and rounded cuticle of the insect and biting attempts were often unsuccessful in penetrating the

cuticle effectively. In this situation the spider seems

to have the capacity to switch in the wrap behavior

unit. Reexamination of the detailed notes on the

behavior of N. maculata towards large acridiids

shows that in one or possibly two cases the spider

commenced wrapping after a long series of bite-andback-off units had terminated in a relatively short

sustained bite; at the time we missed the possible

implications of this behavior.

In only one case did the spider attempt to pull

the prey out of the web prior to wrapping it in

situ and then cutting it from the capture site. The

beetles, unlike the acridiids, did not struggle vigorously during the attacks and made no attempt to

raise the elytra and beat the wings (p. 63). As a

consequence they were not largely freed from the

web when the spider prepared to transport them.

All the prey were transported to the hub on silk

lines and not carried in the jaws.

Temporal Aspects: Total sequence times were

long in duration and average over 12 minutes.

Operations at the capture site (approach, attack,

and packaging) occupy more than half the sequence

time in nearly all cases.

Comparison with Argiope aemula

Nephila maculata ranges from 2 to 4 grams in

weight and is much heavier than Argiope aemula

(0.5-0.9 grams). Despite this fact Argiope takes

less time to attack heavy melolonthid beetles (0.5-

0.8 grams in weight). Durations (in minutes and

seconds) of predatory sequences are given below.

Those for Argiope are for times spent actually in

contact with the prey and include periods of reston-prey (ROP) (two sequences) but not periods of

rest-on-hub (ROH). The latter period is omitted

because the spider is at that stage capable of initiating new attacks and is not occupied with predatory

behavior. Nephila does not have a rest-on-hub behavior. The Nephila attacked all the prey by biting

whereas Argiope attacked all the prey by wrapping.

Arigiope aemula

4:21 ROH

6:40 ROH

4:13 ROH

5:15 ROH

9:18 ROP

8:47 ROP

4:05 ROH

3:24 ROH

6iS9 ROH

11:32 ROH

Nephila maculata

7:57

10-58

8:17

31:10

28:41

12:15

9:18

13:08

11:32

10:29

Robinson, Mirick, and Turner (1969) have argued

that attack wrapping gives the spider the potential

of leaving the wrapped prey at the capture site

without having to wait there until it is sufficiently

subdued to be safely cut from the web and transported. It can thus reduce the time spent away
60 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

from the hub by interrupting a predatory sequence

before transportation and leaving this process until

after a period at the hub monitoring the web. In

the sequences given to live melolonthids the two

that did not involve rest at hub stages were longer

than all but one of those that did.

The wrapping units were extensive and punctuated by short bites or biting attempts. The enswathement of the prey was very extensive and

produced layers of silk that were very thick in

comparison to the effects of wrapping by Nephila.

In fact the wrapping behavior of Argiope looks

much more effective than that of Nephila. It involves synchronous (or nearly so) movements of

the two fourth legs, which cast broad skeins of silk

over the prey in rapid succession. On the other

hand the leg movements of Nephila are slow and

alternating. They carry relatively narrow skeins of

silk onto the body of the prey.

All the beetles were transported on silk behind

the spider; in two cases the insects were wrapped

again at the hub after being hung. Argiope appeared to be able to bite the wrapped prey without

difficulty, although its chelicerae are much smaller

and less heavily sclerotized than are those of

Nephila.

Comparison with Nephila clavipes

Table 10 summarizes the main features of the

attack sequences of Nephila maculata and N. clavipes for a number of types of prey. Robinson and

TABLE 10.—Comparisons of sequence units and durations (in seconds) of N.

maculata and N. clavipes •

Lepidoptera

N. maculata N. cltcviprs

on moths, N=50) (on butterflies, N=20)

Orthoptera

N. maculatn N. clavipes

(on katydids, N=50) (on crickets.N=20)

Dragon Biet

.V. maculata N. clavipes

(N=30) (N=10)

Prey weight (ing)

m

sd

ATTACK UNITS

Bite

m

sd

Pull-out

m

sd

Wrap, & cut out

m

sd

137.3

56.3

15.8

9.5

16.4

13.9

TRANSPORT UNITS

Carry on silk

m

sd

Carry in jaws

m

sd

Wrap at hub

m

sd

Total

m

sd

102.4

SS.0

29.4

18.6

47.6

33.6

1S5.7 (N=7)

25.9

none 16.0 (N= 7)

S.7

Forward Backward

4.4 (N=8) 54.8 (N=42) 285

1.9 22.7 16.4

129.6

30.3

16.6

10.0

162

175

2315

25.8

29.3

17.6

12.8

26.9

110.9

212

445

31.6

522

242

142.7

37.1

63.7

23.7

61.6

55.3

47.0 (N=l)

19.0 (N=l)

Forward Backward

4.0 (N=3)42.8 (N=47) 112

18.4 10.5

101.2 (N=21) •• 75.6 (N=7)

38.6 18.4

44.0 (N=35)

15.0

105.3

43.9

99.6 (N=13)

38.6

228.9

47.9

61.2 (N=50)

19.7

166.6

45.2

50.7

19.8

141.3

47.5

23.6 (N=23)

115

30.7 (N= 7)

175

615 (N=7)

11.6

238.8

61.5

24.9 (N=7)

16.1

53.0 (N=3)

68.7 (N=3)

22.9

210.0

61.3

• Trigona (stingless bees) smallest prey of N. clavipes not strictly comparable with flies

AH sequences are: Bite. Pull out, Carry in jaws, Wrap at hub. Mean total sequence time =

maculata on flies.

•• Two were wrapped after removal from the web (see text).

presented to N. maculata (N=50).

70, sd = 15. See Table 9 for N.
NUMBER 149 61

Mirick (1971) give further details of the predatory

behavior of N. clavipes, including a summary diagram. Generally the similarities between the two

spiders are more striking than the differences. Differences between sequence durations are discussed

below. The other main differences lie in the form

of the behavior units and have been detailed in that

section.

In terms of unit and sequence durations comparisons are complicated by the fact that the insects

presented to the two species were not similar in

size (including weight), morphology, or species. In

order to minimize size differences we have selected

sequences of N. clavipes predatory behavior that

were given to insects that were the closest in size

to those used in presentations to N. maculata. This

selection has considerably reduced the sample sizes

for N. clavipes, all of which are now smaller than

those for N. maculata. This factor may further

complicate the comparison. In addition, it must be

remembered that Nephila maculata is larger, heavier, and has longer legs than N. clavipes. Unlike

Nephila clavipes, which transports prey in the jaws

by walking forwards to the hub, N. maculata backs

up the web, in most cases, when carrying prey in

its jaws.

Despite these differences, and complicating factors, there are overall similarities in some sequence

and unit durations—and in the composition of the

sequences. Thus, with dragonflies of roughly similar

weight, overall sequence times are comparable, even

to range and deviation! Bite and pull-out durations

are similar, but the smaller Nephila clavipes shows

much more variance in pull-out durations. Transportation times for prey carried in the jaws are

higher in the case of N. clavipes, moving forwards

up the slope of the web, than for N. maculata moving backwards. This difference is not statistically

significant but suggests that our inference, that

backing up may be advantageous if prey is bulky,

could be correct. The possibility that it could be

due to the longer stride of N. maculata is to some

extent discounted by the very close similarity of

the durations of carry-on-silk transportation. Both

spiders wrapped this prey in situ more frequently

than they successfully pulled dragonflies from the

web.

Comparison of sequences that N. clavipes gave to

domestic crickets and N. maculata gave to the katydids show that these were similar in duration despite the fact that the crickets were heavier. Only

one cricket was not removed from the web by pulling and no katydids were wrapped in situ. In this

case the process of backing up the web with prey

carried in the jaws (N. maculata) was a lengthy

proccess compared with the process of transportation by walking forward with the prey in the jaws,

carried out by the smaller N. clavipes.

In the case of butterflies, Nephila maculata was

able to free these, in all cases, by pulling them

from the web, whereas N. clavipes wrapped in situ

28 percent of the butterflies, before cutting them

from the web. This fact can be related to the differences in free space, beneath the two species, that

is available for the process of removing bulky prey

by pulling. N. clavipes spent considerably more

time, on average, wrapping prey at the hub after

transportation and this again may be related to

the problem of passing silk over bulky prey when

there is a relatively small amount of free space

beneath the spider. The mean total sequence duration for the treatment of butterflies by N. clavipes

is over twice that taken by N. maculata. This is at

least partly affected by the long duration of the

pull-out, wrap-in-situ, and wrap-at-hub units, in

the case of N. clavipes.

When dealing with small prey of less than .050

grams both spiders give similar sequences of basically similar mean durations. Nephila clavipes attacked stingless bees (Trigona species) by a simple

bite, pull-out, carry-in-jaws, wrap-at-hub procedure.

Nephila maculata attacked slightly larger Calliphora-like flies in this way, although it backed up

the web in 86 percent of the cases. Although N.

clavipes wrapped all the Trigona, on, or shortly

after, arrival at the hub, N. maculata wrapped only

12 percent of the flies within one minute of arrival

at the hub. Flies may be relatively much smaller in

relation to the jaws of N. maculata than Trigona

are to N. clavipes, and there could thus be less

need to secure them by wrapping to prevent them

being lost during further attacks.

Very large orthopteran prey elicited similar attack behavior from the two species (see Robinson

and Mirick, 1971, and above). We did not present

large beetles to N. clavipes but suspect that they

would probably encounter the same problems in
62

handling these prey as N. maculata (and probably

in a more exaggerated form).

Categorization of Araneids by Predatory Behavior

Table 11 gives, in summary form a broad categorization of the predatory behavior of those araneids for which we have data. There are essentially

two major groups of predatory techniques employed

by araneids and the distinction between these two

groups is made on the basis of the presence or

absence of attack wrapping. Further distinctions

or subdivisions of the predatory techniques can be

made within the two major groups on the basis of

the employment of other forms of wrapping behavior. Such categorization would follow that made

by Robinson, Mirick, and Turner (1969) on the

basis of a much smaller sample of araneid species.

We have, so far, found no araneid that shows the

behavior of the hypothetical "Stage 1" constructed

by Robinson, Mirick and Turner (1969:499). This

stage forms one of the alternative sequences found

in most of the Nephila group spiders but does not

occur as the sole predatory technique. We would

predict that if it occurs as a unique technique in

any species existing at present, that species would

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

probably be a small spider within the Nephila

group or a spider specializing on prey much smaller

than itself and possibly building a close-meshed web

of lightweight silk. In such a situation prey could

be bitten, pulled from the web, and wrapping need

only occur at the hub (where it would serve the

function of allowing the spider to store prey caught

during one predatory excursion while it made further attacks on subsequent prey.)

Robinson, Mirick and Turner (1969:500) noted

that some spiders with a isiephila-type attack behavior were able, as a consequence of postimmobilization wrapping, to leave prey in the web

at the capture site and return to the hub to feed on

already caught prey. They thereby were able to omit

the transportation of newly caught prey. This subcategory of a Nephila-type predatory technique was

suggested by studies of one Gasteracantha species

and two Micrathena species in Panama. Studies of

Gasteracantha species in New Guinea confirm that

they too store prey at the capture site (Y. D. Lubin,

pers. comm.).

The occurrence of pull-out behavior in Nephila

species as an almost invariable first approach to

removing prey from the web has been remarked

upon as possibly primitive behavior. We know that

TABLE 11.—Predatory behavior of araneid spiders classified on the basis of principal attack units; sub classification based on prey storage strategies

(US = United States, P = Panama, NG = New Guinea, A = Africa, I = India)

Attack biting used exclusively

No attack wrapping

AH prey stored at hub Some prey left in situ

after attack

Nephila clavipes (P) Gasteracantha cancriformis

N. maculata (NG) (P) •••

N. turneri (A) G. theisi (NG)

N. constricta (A) Micrathena schreibersi (P)

Herrenia ornatissima (NG)

Nephilengys cruentata (A & I) ••

Attack wrapping a major predatory component

Attack biting reserved for some prey items

Prey stored at hub Some prey left in situ

after attack

Cyrtophora moluccensis (NG) • Argiope argentata (P)

A. savignyi (P)

A. florida (US)

A. trifasciata (US)

A. aurantia (US)

A. picta (NG)

A. aemula (NG)

A. reinwardti (NG)

A. aetheria (NG)

Araneus marmoreus (US)

• Y. D. Lubin, pers. comm.

•• Site of prey storage not determined.

•••This species is now known to attack wrap very large prey (determined after manuscript at press).
NUMBER 149 63

it occurs also in Nephilengys species. The size of

prey that can be removed from the web in this way

may ultimately depend on the relative length of

the spider's legs i, u, and iv, which determines the

maximum distance between the spider's body and

the web surface. This, in turn, determines the free

space available for removing and manipulating

prey. Other factors, presumably including the deformability of the web plane may restrict the

practicability of using the pull-out technique for

removing prey. Herrenia ornatissima may be unable

to use the pull-out technique on larger prey because

its legs are relatively short (compared to those of

Nephila species) and also because deformations of

the web plane could result in parts of it being

pushed against the nearby tree trunk and adhering

thereto. Spiders that build close-meshed webs may

not be able to free prey by the pull-out technique

unless they immobilize them very rapidly, i.e., before the prey's struggles enmesh it inextricably.

Nephila species are remarkably fast in their movements across the web, this too may be a consequence

of having relatively long "sprinters" legs.

The occurrence of wrapping after a series of

apparently abortive biting attempts in the attacks

on very large, or heavily armored, prey by Nephila

maculata is oi interest for two reasons. First, it

suggests that wrapping behavior is not necessarily

triggered by the stimuli that the spider receives

as a consequence of a successful attack bite, as

Peters (1931) claimed for Araneus diadematus. It

could, however, still be triggered by the act of

biting. In cases where the chelicerae do not penetrate there is no possibility of the spider testing

the edibility of the prey by taking in materials from

within the insect cuticle. In such cases the decision

to proceed with the predatory act must be based on

the perception of stimuli derived from the outside

of the prey. Secondly, the occurrence of wrapping

behavior in the absence of prior successful biting

can be regarded as a possible first step in the evolution of attack wrapping. As such it is of prime

interest.

BEHAVIOR OF PREY IN THE WEB

In the course of presenting a wide variety of prey

to Nephila maculata we made a large number of

incidental observations on the behavior of the prey

items after they had become enmeshed. These are

of some interest since they indicate different escape potentials of prey when the spider is present in

the web. Since the prey were mostly thrown into

the web by the experimenters their initial orientation may be unnatural and this could affect their

subsequent behavior. However, if some of these

prey show escape movements that are wholly or

partly effective, there is good reason to assume that

prey arriving in a more natural manner would be,

at the very least, as likely to escape.

In general only very small prey and very large

prey tend to escape if the spider is present and

reacting normally. Otherwise, the approach to the

prey is so rapid that the spider is attacking before

they prey has had time to free itself. Lepidopterans

are an exception.

Of the very large prey the acridiids kick vigorously when in the web and these movements,

together with their weight, cause extensive tearing

of the web so that they slip downward towards the

lower margin and may then escape. In addition, our

data suggest that a vigorously kicking, large acridiid

is approached much more cautiously than an inert

one and this may gain the insect escape time. Furthermore, even when an attack has started (and is

at the protracted bite-and-back-off stage) the spider

may be repelled by vigorous kicking and the prey

may be able to escape. We have long suspected that

orthopteran regurgitants may affect spider silk but

have not investigated this matter. Most large beetles

struggle when in the web and may slip to the edge

and escape. Their relatively short legs have a much

less dramatic tearing effect on the web, but the

movements that they produce may help to loosen

the attachment of the prey from the viscid element.

It is noticeable that they close their wings and

elytra in the web, thus presenting a compact smooth

mass. In general large beetles seem to have a much

smaller surface area/weight ratio than large acridiids and therefore, per unit weight, have less surface in contact with viscid droplets. They thus slip

out of contact with adhesive fairly rapidly. After

watching the wrapping attacks of Argiope aemula

on beetles, we are struck by the fact that relatively

smooth cuticle presents a much more difficult surface on which to deposit enswathing layers than

does the cuticle of orthopterans. If viscid droplets

adhere less strongly to shiny surfaces, some beetles
64 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

could have a higher escape potential than others—

beetles and insects.

We have no records of lepidopteran escapes

from our prey-analysis studies. When throwing

moths into the web during the studies on predatory

sequences we found that a number did not adhere

sufficiently to remain in the web until the spider

arrived. In these cases vigorous fluttering movements apparently facilitated escape.

Very small prey items, e.g., nematocerans and

small hemipterans were ignored by the adult female

Nephila even when struggling. Some of these are

certainly consumed by kleptoparasites, but some

may escape. We suspect that when rain wets the

web small insects that have not been attacked may

be liberated.

RESPONSES TO ENVIRONMENTAL FACTORS

SUNLIGHT.—Many tropical insects that assume

more-or-less immobile resting attitudes by day

change their orientation in apparent response to

changes in the direction of incident sunlight. Thus

many orthopterans minimize heat absorption by

aligning themselves with their long axis parallel to

the sun's beams. Kettlewell (1959) noted this in

the case of Brazilian katydids, and Uvarov (1965)

has reviewed reports of this phenomenon in acridiids. There are some reports of spiders assuming

a special orientation with respect to the sun's

position. Thus Pointing (1965) showed that the

linyphiid Frontinella communis (Hentz) would

orient to the sun's disc in both horizontal and vertical planes unless it was in the shade or at web

temperatures below 30°C.

Krakauer (1972) has studied the thermal responses of Nephila clavipes and found that at temperatures of above 35°C the spider orients the tip of

its abdomen towards the sun and thereby reduces

the radiant heat load on its body. In addition he

found that the spider may also employ evaporative

cooling by extruding liquid from the chelicerae.

Krakauer"s experimental technique was to place

heat lamps above the middorsal area of the abdomen of captive spiders, but he did not experiment

with spiders in the field. He does however suggest,

on the basis of field records, that Nephila clavipes

builds its web oriented in a plane normal to the

area of maximum insolation and that the tilt of

the web to the vertical faciliates postural thermoregulation by reducing the angle at which the

spider has to hang in order to point at the sun

when this is at its zenith.

Our attention was independently drawn to the

response of Nephila maculata to bright sunlight

when we found a mature female standing with her

long axis more or less at right angles to the web,

facing away from the sun. This complex posture is

shown in Figure 30, and is the reverse of that figured by Krakauer (1972, fig. 2). Despite the difference in position the total effect is presumably the

same, i.e., the minimum surface area is exposed

to radiant heat. We assume that positions such as

this are not so economic of energy as those involving aiming the abdominal apex at the sun but

become necessary because of web orientation.

To investigate further orientation to the sun we

mounted a circular mirror on a tripod and then

manipulated the apparent position of the sun by

directing sunlight onto spiders that were otherwise

in the shade. In this way we elicited responses to

"impossible" positions of the sun. Such positions,

e.g., when the sun was apparently shining upwards

from below the web elicited orientations that made

adaptive sense, the spider aligned itself as though it

were minimizing heat absorption from this improbable heat source. We were also able to induce

movements of spiders across the hub region through

more than 90 degrees of arc in a few minutes and

thus replicate the effects of several hours of azimuth

shift.

We did not have the necessary equipment to

monitor temperature at the surface of the spider

but black bulb temperatures were in excess of 30°C

when we made our observations. Clearly spiders

have a capacity of postural thermoregulation, which

includes positions that are more complex than

would be necessary if the web were always simply

oriented to be normal to the area of maximum

insolation. In fact many of the postures may involve

the spider in energy-consuming attitudes, but presumably these need not be adopted for very long

periods in most tropical regions where uninterrupted sunlight (except in dry season periods) may be

unusual. Nephila maculata seldom builds out in

the open and may thus be shaded for long periods,

even when there is uninterrupted sunlight in open

areas. We are strongly inclined to think that web-
NUMBER 149

FIGURE SO.—Ncphila maculata orienting to strong sunlight, which is passing through the web

from the right of the picture. This spider has lost the left leg i and right leg it.
66

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

site choice is much more likely to be determined by

availability of supporting structures (and predatory success) than by the necessity for economizing

in energy expenditure on postural thermoregulation.

One point that emerges from our observations as

worthy of further investigation is the extent to

which heat and visible light interact in mediating

the orientation of thermoregulating spiders. It

seems entirely possible that temperature may trigger

the response of postural thermoregulation (as suggested by the work of Pointing, 1965, and Krakaeur,

1972) while the actual orientation may be based on

responses to visible light. We made no attempt to

determine whether the spider's eyes were involved

in the sunlight response, but are currently doing

so in experiments with Nephila clavipes.

RAINFALL.—Pointing (1965:73,75) has noted that

his spiders responded to heavy precipitation by

moving to positions in the barrage of threads above

the sheet web. There they assumed head-down

positions until the rainfall ceased. However they

responded to less heavy raindrops—but heavy rainfall—as they responded to sunlight, i.e., by presenting the minimum surface area to the rainfall. From

our observations on Argiope argentata in Panama

we know that some spiders may adopt special rainfall

postures if they remain in their webs and do not

seek shelter under nearby vegetation. Thus Argiope

argentata hangs away from its sloping web so that

the body is almost perpendicular and legs i and n,

which are always directed anteriorly, are off the

web. In the rainfall posture these two pairs of legs

are held outstretched in line with the midlateral

plane of the body and at a fairly acute angle to

the long axis, i.e., they are held more anteriorly

than in the normal resting attitude. This position

could be interpreted as minimizing the crosssectional area exposed to the rain—assuming that

tropical rains fall more-or-less vertically—or that

the spider in this position maximizes the flow of

water off its body surface with the anterior appendages forming a sort of drip-tip. We have since

seen this behavior in Nephila clavipes, and Leucauge species. In the latter case the spider hangs

almost vertically, head down, from its horizontal

web. Charezieux (1967) has described a rainfall

position adopted by Nephila madagascariensix.

Nephilia maculata responds to heavy rain by

cutting away areas of web (p. 10) and may then

retire to shelter under the leaves of nearby vegetation. Continuous fairly light rain can evoke the

web-cutting response, but the spider may then remain at the hub of the partially dismantled web.

When it does this it assumes a position somewhat

similar to that assumed by Argiope argentata. Figure 20 of N. maculata essentially shows the basic

attitudes of the legs when the spider is responding

to rainfall. The rainfall posture differs from the

plucking only in that the spider hangs away from

the inclined web, more or less in a vertical position,

but with the abdominal apex tucked in against the

web.

DEFENSIVE AND ESCAPE BEHAVIOR

Nephila maculata exhibits behavior that can be

categorized as defensive because of its form and/or

context. Touching the spider lightly on its dorsal

surface (unprotected by the web) evokes a characteristic posture. In this the prosoma is raised anteriorly and the total length of the body assumes a

concave dorsal orientation. The posterior margin of

the prosoma thus becomes pressed against the anterior margin of the opisthosoma at the waist joint.

In addition, the first two pairs of legs are flexed

and raised off the web. This posture may be a defense against aerial predators or parasites. The body

flexure could protect the possibly vulnerable waist

and position the body so that the legs can be used

to fend-off insects attacking from above. The raised

legs may constitute a barrier to such attacks since

they are held over the prosoma. Because these legs

are not gripping the web they may be instantly

available for defensive movements.

Escape movements occur in response to disturbance of the barrier web or to violent movements

within the orb. The spider invariably runs upwards

onto upper frame members and often into the

shelter of surrounding vegetation. Whether or not

the escape run terminates on a frame thread or in

vegetation seems to be largely dependent on the

strength of the initial disturbance and whether or

not it persists. We have not been able to quantify

this. The form of the escape run is often distinguishable from a predatory run because it includes

dorsoventral "bouncing" of the body.
NUMBER 149 67

Discussion

This study spanned one year, on a day to day

basis, and touched on many aspects of the biology

of Nephila maculata. Despite its wide scope, it is

only an introductory investigation into the bionomics of the species and thus we can raise in

detail the more general questions that the study

provokes and outline some of the principles that

have emerged.

PHENOLOGY

In terms of seasonal patterns of predation exerted

by large trap-building spiders we have added data

from a much less climatically variable area than

that where we carried out our study of the prey of

Argiope argentata (Robinson and Robinson, 1970a).

Differences between the results of the two studies

are not, unfortunately, ascribable to the differences

in climatic pattern alone. Two different techniques

were used to determine the number, nature, and

temporal distribution of the prey caught by two

spiders of distinctly different ecologies. From data

on population dynamics, in addition to the data

from the prey-capture studies, we feel confident that

Nephila maculata in the more equable (than Panama) climate at Wau, is able to subsist throughout

the year without major perturbations. This raises

a question that seems to bedevil many studies of

animal phenology in the tropics. How typical was

the year during which the study was carried out, or

how consistent are long-term patterns of climate?

Indications from Barro Colorado suggest that there

may be major differences between the dry seasons

in the amount of rainfall, to name only one factor.

Thus the dry season after our study of Argiope argentata in Panama (Robinson and Robinson, 1970a)

was much wetter, and the present dry season (1972)

has been distinguished by an abnormally high

January rainfall. At Wau there are indications of

very considerable fluctuations in the annual distribution of rainfall. Thus, in May 1970 the rainfall

at our study site was 2.8 inches and in the May

following our study the rainfall was 7.7 inches.

Brookfield and Hart (1966) give coefficients of variiaton (cv) for the monthly rainfall at the Wau

number 1 station, based on 28 years of complete

data. All months show more than a 30 percent coefficient and four months (January, May, August, and

October) show more than 50 percent. These authors

also give the standard deviations for monthly rainfall at this station, which also reflect the great

variability. Brookfield and Hart (1966:14) define

areas of high variability for annual means as those

with a coefficient of variability greater than 25 percent. Wau number 1 has an annual cv of 15 percent. The annual variation may be much less important to some organisms than the short term

variations.

What aspect of rainfall may most directly affect

web-building spiders is presently unknown. The

operation of a trap that is damaged by rainfall

could be affected by the number of discrete rainfall

periods per day, the intensity of the rainfall, the

number of successive days of rain, and so on. We

have plotted web renewal and prey-capture figures

against some of these aspects of rainfall, but there

are no simple correlations. Similarly we need to

know much more about the effect of the various

aspects of rainfall on the different developmental

stages of the spider before we can assess the effects

of this factor on the biology of the species. Small

webs produced by immature stages may be more

susceptible to damage by rain than the stronger

webs of adults; but, on the other hand, they may be

built in more sheltered sites. Such sites may be

available to immatures with small webs whereas

adults may only be able to build their webs in more

exposed sites. The complexities are immense. Many

biologists accept climatological data from one point

in an area and use this to interpret biological data

from the entire area. Perhaps this is a valid technique for some organisms and some aspects of their

biology. It is interesting to note that the three

Wau rainfall stations, separated by less than 1

kilometer in horizontal distance, and 150 meters

in height, show very considerable differences in the

temporal pattern of precipitation.

Since our data on web adhesiveness suggest a

correlation between this factor and relative humidity, periods of rainfall that do not result in

raindrop damage to the web may be more favorable

to the spider than periods when the efficiency of

the adhesive droplets could be adversely affected by

low humidities. This is yet another factor to be

considered as part of the complex interaction

between the arachnid and climate. It is usual to

delimit seasons by rainfall and temperature criteria
68 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

and many of the climographs used by biologists

plot these two factors (Richards, 1957). D. Leston of

the University of Ghana (pers. comra.) has suggested that hours of sunlight may be crucial to

many organisms and, if these are considered, some

tropical areas with two grossly distinct seasons in

terms of rainfall and temperature then have three

seasons. Since many orb-web spiders have responses

to sunlight plus radiant heat, variation in hours

of sunlight may affect them directly as well as indirectly.

Web-building spiders could also be affected indirectly by the influence of climatic factors on the

structure of their habitat. Web supports for the immature stages of spiders, such as Nephila maculate,

may depend on the presence of ephemeral nonwoody vegetation (herbs and forbs). These may

cycle in abundance during the year in many parts of

the range of the species. This is certainly true, from

our own observations, of the Bombay site where

Thakur and Tembe (1956) studied the species.

Even such apparently obscure factors as a period

of heavy production of wind-dispersed seeds could

affect the success of spiders, since their webs may

trap very large numbers of them and become conspicuous and ineffective. Large-scale leaf-fall may

have a similar effect and also increase the amount

of sunlight reaching the area of the forest in which

the spiders build their webs. Apart from increasing

the drain of energy involved in thermoregulation,

increased illumination could then render the webs

and spiders more conspicuous to predators, prey,

and parasites.

Our phenological studies were primarily concentrated on variations in the weight and nature of

the prey items with time. The data are too crude

to permit anything more than guesses about their

significance. This is a complex field. It seems possible that there may be differences between adult

female Nephila in the caloric input necessary to

maintain a regular egg-laying routine (whatever

that may turn out to be). Thus there are certainly

considerable differences in the size of adult females,

other than those of expandable parts such as the

opisthosoma. Small females presumably have a lower caloric requirement than adults of large size. We

have no baseline from which to calculate the maximum rate of egg-sac production. It seems quite

possible that the minimum interval between egg

masses may be fixed physiologically and that the

animals can adjust to variations in food supply by

altering the number of eggs in the egg sac and

extending the period between layings. Certainly

the increase in the size of the opisthosoma prior to

egg laying is very striking and may represent a

considerable increase in weight. We have no idea

if there is an upper limit to food intake that could

be achieved under normal conditions in the field.

Questions about the relationship between food supply and egg production could, perhaps, best be

answered by a laboratory study with captive specimens.

The fact that the total weights of prey remnants

varied, on a weekly basis, between less than one

gram to nearly five shows that there were (at least

relatively) lean weeks and rich weeks. Detailed

analysis of the data shows that lean weeks are lean

weeks for all spiders. Thus in week 47 (commencing

14 April 1971) the total catch was .958 grams.

No spider was responsible for more than 210 mg,

5 spiders caught more than 100 mg, 5 spiders caught

less than 100 mg. In rich week 24 (commencing

28 November) with a total of 4.670 grams of food

remains, two spiders accounted for more than 1

gram of remains each, two spiders exceeded 500 mg

in rejected remains, three spiders exceeded 200 mg

and the remainder fell below this. Thus the spread

on the good weeks is greater than that on the lean

weeks.

The spiders should, presumably, be attempting to

maximize their catches and could be expected to

show some evidence of smoothing the variations in

the abundance of potential prey by behavioral adjustments. Thus they could attempt to compensate

for low catches at one place by moving the location

of their webs. In addition, they might feed on some

organisms, during periods of low catches, that they

would reject when food was abundant. Our data

do not show a positive correlation between predatory success and stability of web site, nor, unfortunately, a negative correlation between movements

of web sites and low returns of prey. The influence

of other factors could mask such effects. Nor have

we any evidence that the spiders accept some types

of prey, during periods of relative food shortage,

that are rejected at other times. Despite this, we

thought that the effects of the spider's behavior

might result in there being less variability in the
NUMBER 149

numbers of the prey that they caught than there

was in the numbers of insects caught by the

window-pane traps. This proved to be the case;

but since the means of the two samples are quite

different this evidence is, at the most, only suggestive.

Turning to the phenology of population increments, it is obvious that it is necessary to conduct

detailed studies on the developmental rates of the

two sexes, under different feeding regimes, and at

different times of the year, before we can begin to

elucidate this problem. Collection of egg sacs leading to estimations of the fertility of the eggs, the

developmental period and factors that influence it,

conditions favoring eclosion and subsequent dispersion, are all necessary and practicable further

steps in the study.

Studies carried out in the relatively benign climatic regimes of upland tropical areas like Wau,

should provide some clues about how widely distributed species manage to cope with the more

extreme climatic regimes in other parts of their

range. (Tropical is here used in the sense of Richards (1957:135), i.e., it applies to the area that lies

within the isotherm of 20°C mean annual temperature.) We can ask whether the adaptations which

enable N. maculata to exist under the very different

climatic regime at Bombay already exist in the

Wau population. Evidence from the fringe habitats

in the Wau area suggests that they may not.

Levy (1970) has suggested that the life cycles of

spiders may fall into two broad categories based

on the developmental rates of the two sexes. In one

class are the majority of spiders studied so far

(primarily temperate region), in which spiders of

both sexes that derive from the same cocoon reach

maturity at the same time. In the second class are

those spiders in which the sexes mature at substantially different rates (siblings could not mate). Levy

(1970:534-535) suggests that there are two strategies that would insure a coincidence of adult males

and females in the latter case. These are that cocoons should be produced throughout "long periods

of the year," or that there should be two adult

phases in the year with males of one phase coincident with females of the previous phase. He suggests

that, in the case of Nephila madagascariensis, the

two phase system may operate. Bonnet's (1930) data

show that males mature in approximately a quarter

of the time necessary for females to mature. Our

data show that there are mature males and females

present throughout the year and copulation plus

egg laying is occurring throughout the year. In

Bombay the same species has an apparently one

phase reproductive cycle (like a temperate species).

This aspect of adaptive reproductive strategy on the

part of Nephila maculata could either be a result

of the direct influence of different climatic regimes

or be due to genetic differences in the reproductive

biology of the spiders in different parts of their

range.

BEHAVIOR

Nephila maculata is the second tropical member

of this genus whose courtship behavior has been

studied. The discovery of the complex silk-deposition activities of the male adds a new element to

ihe picture of araneid courtship behavior. Generalizations about araneid courtship have, so far, been

almost entirely based on studies of north temperate

forms. We think that further comparative studies

of tropical forms are essential if the evolution of

courtship behavior is to be understood. The possibility that silk deposition may be a primitive

condition cannot presently be rejected. The occurrence of this or similar behavior in other species

and genera may have been missed by students,

because of the practical difficulties involved in seeing large numbers of courtship sessions in seasonal,

and widely dispersed, temperate forms.

Our observations on the predatory behavior of

Nephila maculata, other Nephila species, and

Nephilengys and Herrenia, as well as the study of

Argiope species in New Guinea, show that these

species conform to the overall categorization of

araneid predatory behavior provided by Robinson,

Mirick, and Turner (1969).

The experiments with large melolonthids as prey

show that the absence of attack wrapping in the

Nephila group of spiders places them at a disadvantage, compared with spiders that have attack

wrapping, in capturing large prey. This raises the

question of why the Nephila species have not been

out-competed by Argiope species (or other advanced spiders). No existing Argiope species appear

to occupy quite the same niche as the Nephila

species. Furthermore all the Nephila species that
70 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

we have seen build large strong and relatively finemeshed webs that are operated day and night. Other

large spiders that build webs of comparable size

(e.g., Eriophora fuliginea, see Robinson, Robinson, and Graney, 1972) operate them principally at

night. At night, moths may constitute a large proportion of the prey and attack biting is the most

effective strategy for dealing with these insects.

There is probably an advantage in sheer size when

operating a large web. (The immatures, probably

in the same zone of the forest habitat as Argiope

species, have at some stage, webs that are similar

in size, and they may be more close to niche overlap at this stage).

The sun-orientation behavior that we have described raises some interesting questions since, as

far as we know, it does not occur in Argiope species

that build webs in positions that are more frequently exposed to direct sunlight. There are a

number of possible explanations of this difference.

Argiope species may orient their webs so that the

spider does not receive radiant heat on its black,

ventral surface but on its reflectant dorsal surface.

What evidence we have does not support this theory. There are very considerable differences in the

surface to volume ratios between the smallish, flattened, Argiope species and the large cylindrical

Nephila species, which must have less surface area

per unit volume than the Argiope species. This

should lessen the heat load that they have to compensate for but increase the problem of heat dissipation once they become heated. The brain, situated in the prosoma, may be an organ that is

particularly sensitive to high temperatures and it is

worth noting that all the Nephila species that we

have seen have silvery (possibly reflectant) dorsal

coloration of the prosoma.

Stabilimentum building by immature Nephila

maculata, the first records of this phenomenon for

the genus, raises interesting questions. It seems unlikely that this implies any close relationship with

the genera of spiders that presently build ribbon

stabilimenta. If it was evolved independently and

is now a vestigial character in Nephila maculata

what was its original function? Similarly the construction of orb-like barrier webs by juvenile N.

maculata is a newly described piece of behavior and

may have important implications from the standpoint of defense against predators, suggesting that

the immature stages that build such barriers may

be particularly susceptible to attack by flying predators. It might also be a clue about the origins of

barrier webs in general.

We have since discovered that in Panama immature Nephila clavipes build complex structured

barrier webs that are drawn away from the main

web at their centers and are conical. These are

similar in gross structure to those described for

N. maculata (p. 10), but do not have an orderly

spiral. They are most complete above the dorsal

surface of the spider where there may be two distinct plane structures. Above the main orb, ventral

to the spider, there is usually one plane structure

and a second supporting complex. The existence of

a triple barrier (two plane structures and one supporting structure) above the spider suggests that

this complex may be defensive. The spider must

be protected from below by the main orb as well

as the secondary structures. Full details of the

juvenile barrier webs of Nephila clavipes, with

photographs, are to be published separately.

We suspect that almost any long-term studies

of tropical spiders would reveal suggestive, new,

information about their behavior and ecology. This

is part of the fascination of spiders.

Addendum

Since this study was at press, new information has become available on two subjects dealt

with herein: (1) Stabilimentum building by Nephila species (pp. 8-19, herein). It has been

discovered that, on rare occasions, Nephila clavipes builds linear ribbon stabilimenta. Details

and comments on the possible evolutionary significance of these structures, will be given by us

("The Stabilimentum of Nephila clavipes and the Origins of Linear Stabilimenta in Araneids,"

Psyche, in press). (2) Postural thermorcgulation by Nephila species (pp. 64-66, herein). The

repertoire of thermoregulatory postures of Nephila clavipes is now known to include an

analogous posture to that described herein and illustrated in Figure 30. A detailed analysis of

the thermoregulatory behavior of N. clavipes is in preparation ("Adaptive Complexity: The

Thermoregulatory Postures of the Golden-web Spider Nephila clavipes at Low Latitudes.").
NUMBER 149 71

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Appendix 1

Activities of Male Nephila tnaculata during Courtship Silk-deposition

(Notes on two-hour observation session; time intervals omitted, except for long rest periods; silk attachment occurs at all points

listed)

Start: male moves from dorsal surface abdomen

(DSA) onto base of third leg left (3L), to surface

abdomen, right then left, to 4R then across thorax

to 4L, 3L, back to DSA right, pause 2 min.+, DSA

left, to 4L, to 4R, 3 and 2R rapidly, then 4L, 3L,

2L, back to DSA right, then 3R, 2R, 1R, DSA left,

pause 1.40 min., then to 4L taps leg base, 3L taps

leg base DSA right, three silk attachments, then

4L, 3L, 2L, to DSA left one attachment, 4R, 3R,

2R, 1R, then DSA left, DSA right, then 4R, 3R, 2R,

4L, 3L, 4R, 3R, 2R two attachments, DSA and

pause left, then right, rest 1.20 with legs 1, 2, on

bases of female leg 4R, then move to halfway up

female DSA, then back to abdominal margin right,

4L, 3L, 2L then between 2-1L, DSA left, pause

2.10 on outer edge, touching legs of female, then

DSA right, pause 3.15, 4L, 4R, 3R, between 3-2R,

4L, DSA center, 4L, DSA right pause 2.25, DSA left

two attachments, 4L, 3L, 2-1L, 4R, 3R, 3-2R, DSA

right pause 1.00+, move halfway up right DSA,

pause 2.05, 4R, 3L, 4-3R, 3-2R with two attachments below leg bases, DSA right 4.00, DSA edge

right taps bases of female legs 2 and 3R (apparently feeling beneath female's legs, 3.30, 3L, 3-4L.

4R, 3-2R, 4L, DSA right, then against raised anterior edge of abdomen as female attacks coccinellid

beetle beetle rejected, female backs up web to hub,

male remains on scarp of abdomen, female strokes

the base of her legs 4, 3, 2L with tarsi of opposite

legs 2, 3, as though feeling the silk deposited by

the male, silk now clearly visible as a gusset at the

leg bases, male inactive for 2.30 min., female plucks

web in response to gust of wind, male moves to

4R, underneath 4R, 3R, 2R, 1R, 2R, then DSA

median position, 4L, 3L, DSA median, DSA right,

4L, DSA right, rests 2.00+, 4R, 4L, 2L, 3L, all wellup from leg bases, DSA right in upper half abdomen, 2R, 4L, 3-2R, DSA center, 4L, 3-2L, DSA

center about 8mm from edge, male feels between

2-3R, 3-4R with legs 1 and 2, DSA right 1.12 then

4R, 3R, 2R, DSA left, 4L under, 3L under, DSA

right pauses 40 sec. touching 4R with legs, then

4-3L, 2L, 4R, 3R, 2R, 1R, 4L, 4R, DSA right rest

1.00+3R, 2R, 4L, 4R, 3-2R, 2-1R, DSA right 3-2L,

2L, 1L, 4R under, SR, 2R, DSA left rest 2.32, 3-2L,

2-3R, 4L under, 3L under, 4R, 3-2R, DSA right,

DSA left, rest 2.05 tapping 4R, 3R, 4-3R, 2-1R,

DSA right backs up to abdominal apex and attaches

line, returns to edge tapping occasionally 2.45,

down to 4R, 3L, 3-2L, 4-3R, 3-2R, DSA left rest

tapping 4, 3L 1.43, 2-3R, 3-4L, 3-2L, 1-2L, 4R,

3R, 2R, all under, DSA midline 1.00+, moves underneath female abdomen sideways, on top again,

4L, 4R, 1R, pedipalps!, 4L, DSA right, sidles to

underside of abdomen advances down, then, on

top, 1L, pedipalp L, 1R, 2R, 2-3R, 2-1L, DSA

right, pauses 2.20, then sidles under abdomen and

quickly back, again under approaches epigyne taps

with pedipalps, taps again, alternating movements,

Pinsert right pedipalp momentarily, then left, left

still down, standing with right legs 1, 2, on base

of female legs—2 minutes insertion ???, male shuttles up onto DSA after observer accidently touches

web foundation line, motionless, touches 4R, 4L,

1-2R, 4R under, 1-2R under, DSA right 1.00+, 4R,

3R, 4R under, 3-2R, 2-1R, DSA left rest less than

1.00, 4-3L, 2-1L, 3-2R, 4-3R, DSA midline then

up to apex abdcmen, insect strikes web female

responds immediately, male stands on scarp of

abdomen—is this a response to female's movement?,

prey escapes rest 2.00, male moves up to DSA from

scarp, female cleans pedipalps, rests 2.12, then

spends 5.00+ on DSA intermittently tapping leg

bases of female . . . [MHR's observation period

ended, BR takes over].

Down to 3R, DSA median 1.10, 4L, 3L, 3L, DSA

right, pauses 2.40, cleaning feet. 2R, 3R, 1R, 2R

under, DSA center 3.10, 2L, 3L tapping, 3R-4R,

74
NUMBER 149 75

2-3L, DSA right rest 1.40, 3-4L, 3-4R, 2-3L, 3-4R,

DSA left, 2-3-L, DSA right, rest 2.10, 1-2L, pedipalp L, 3-2R under, 2-3L, 4R, DSA median 2.20,

2-3R, DSA center rest 1.40, 2-3L, 3-4R, 2-3R, 3-

4L, 3-2L, 3-4R, 3R, DSA center rest less than 1.0,

chelicerae R, 1R, chelicerae L, 3-2L, 3R, 2L, 3R,

2L, 3R, 3R, 4R, DSA center rest less than 1.00,

apex of abdomen, down ventral surface of abdomen, shuttle to DSA center, 4R, 3R, 3L, 4R, 3R,

4L, 3L, 3R, 4R, 2R, 3-4L, DSA right rest 2.18, apex

of abdomen, down dorsal surface to scarp right,

rest 1.10, web blows in wind, male stationary.

Female cleaning and moving abdomen as if trying

to remove male, swings off web so that all legs on

one side can scrape at male.

End of session: 2 hours; time spent in silk attachment, approximately 49.55 minutes.
Appendix 2

Verbatim Notes on Selected Sequences Given to Large Acridiids

(See pages 57-58, for background)

Behavior

Presentation 1: 50 mm acridid

Pluck

Slowly down to prey

Touch

Move down y2 in., tap with legs i, raise

these back off web over thorax in defensive posture

Lunge forward, bite, back-off

Motionless

Edge forward until pedipalps contact prey

Lunge forward over prey, bite, back off

Motionless

Lunge, bite

Sustained bite on second right leg of prey

Move bite location, in short steps to right

thorax

Short biting attempts jaws edgewise to

tough thorax

Return to biting prey leg 2R

Shift bite to junction of leg 1R and

thorax

Small bites at thorax edge

Wrap prey (x82)

Cut out and pull

Wrap (x28)

Cut out

Wrap (X16)

Cut out

Carry on silk, supported by both legs iv

then left iv

At hub

Turn right, attach carry-silk 3 times

Pause and clean, feet, chelicerae, pedipalps

Pull up prey, handle, then feed.

Total sequence time 28:42

Elapsed time

(min.'.sec.)

0- 0:09

0:10- 0:18

0:18- 4:15

4:15- 7:40

7:40- 7:42

7:4S- 9:20

9:21- 9:28

9:20- 9:32

9:33-11:50

11:51-11:57

11:58-15:05

15:05-15:10

15:11-15:18

15:19-17:30

17:31-21:25

21:26-22:20

22:21-23:15

23:16-23:34

23:35-24:12

24:13-24:56

24:57-25:08

25:09-26:39

26:40-27:10

27:10

27:11-27:38

27:39-28:40

28:41-28:42

Presentation 4: 50 mm acridtid

(The absence of a substantial bite in this

be noted.)

Retreat to 18" above hub on upper foundation thread

Edge slowly down to hub

Slowly approach prey, legs i k II (x')

raised off web, pluck

Halt 8" from prey

Resume slow approach

Touch with legs i

Touch with legs II as well

Palpate

Lunge, bite, back-off

Pause, motionless

Lunge, bite, back-off

Pause

Lunge, bite, back-off

Pause

Lunge, bite, back-off

Pause

Lunge, bite, back-off

Pause about 3" from prey touching it

with 2 legs i, one leg II

Move dose to prey and palpate along

dorsal surface thorax to head

Turn left and wrap (x8 6 ) cutting

intermittently

Cut along upper surface of prey and

attach line to intact web above

Palpate down to head

Cut out below

Wrap (Xl6)

Cut above

Wrap (X8)

Cut final attachments

Carry on silk with support from both

legs rv

At hub

Turn right at hub and attach silk 4

times

Manipulate prey

Feed

sequence should

0:01- 2:02

2:03- 2:18

2:19- 3:10

3:11- 3:17

3:18- 3:51

3:52- 3:55

3:56- 4:10

4:11- 4:22

4:23- 4:25

4:26- 4:34

4:35- 4:38

4:39- 4:46

4:47- 4:50

4:51- 5:07

5:08- 5:10

5:11- 5:16

5:17- 5:25

5:26-12:40

12:41-13:12

13:13-16:25

16:26-16:42

16:43-17:08

17:09-17:27

17:28-17:51

17:52-17:57

17:58-18:05

18:06-18:35

18:36-19:15

19:16

19:17-19:23

19:24-20:18

20:18

•& U. B. GOVERNMENT PRINTING OFFICE. 1*7» 8t«-*X4/*2

Total sequence time 20:18

76
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