The Ecology and Behavior of

Nephila maculata: A Supplement

MICHAEL H. ROBINSON

and

BARBARA ROBINSON

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 218
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SMITHSONIA N CONTRIBUTION S TO ZOOLOG Y • NUMBER 218

The Ecology and Behavior of

Nephila maculata: A Supplement

Michael H. Robinson

and Barbara Robinson

ISSUED

MAR 2 5 1976

SMITHSONIAN INSTITUTION PRESS

City of Washington

1976
ABSTRAC T

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

maculata: A Supplement. Smithsonian Contributions to Zoology, number 218,

22 pages, 9 figures, 1 table, 1976.—Further studies of the subject of Smithsonian

Contributions to Zoology, number 149, have filled in gaps in that study and are

reported herein. Analysis of data on the web-site constancy of Nephila maculata

shows that this spider may, as an adult, spend considerable periods at one site.

It almost invariably moves after egg-laying, possibly as an antipredator device.

The spider may also move its web site when catching above-average quantities

of prey. Such apparently purposeless moves reduce the numbers of theridiid kleptoparasites associated with the Nephila web and this may be their functional

significance. It is here reported that N. maculata builds stabilimenta into its

molting webs (that lack a viscid element). The egg cocoons of the species are

described, numbers and weights of eggs are given, and it is suggested that the

structure of araneid egg cocoons may be a useful character for elucidating relationships within the family. Instances of mammalian predation of araneid eggs

are described and a full account is given of size and color changes in the developmental history of N. maculta. Males of this spider need only 7 molts to reach

maturity whereas females need 13. Mature males and females from the same

batch of eggs probably do not overlap in time. Details of the association between

a moth and Nephila webs are reported and the relationship is discussed; the

moth probably gains protection from association with an aversive structure.

Observations show that birds may learn to avoid contact with large araneid webs.

New observations on courtship and thermoregulatory behavior are detailed.

Courtship includes a preliminary approach stage in which males may react

aggressively and displace one another. Copulation times may be much longer

than previously reported. The thermoregulatory repertoire of N. maculata is at

least as large as that of the other Nephilia species studied so far.

Adult female N. maculata are used as food in several parts of New Guinea.

Methods of cooking and the general flavor are described.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year. SI PRESS NUMBER 6138. SERIES COVER DESIGN:

The coral Montastrea cavernosa (Linnaeus).

Library of Congress Cataloging in Publication Data

Robinson, Michael H.

The ecology and behavior of Nephila maculata.

(Smithsonian contributions to zoology ; no. 218)

Supt. of Doc. no.: SI 1.27:218

1. Nephila maculata. I. Robinson, Barbara, 1931- joint author. II. Title. III. Series: Smithsonian Institution. Smithsonian contributions to zoology ; no. 218.

QL1.S54 no. 218 [QL458.42.A7] 591'.08s [595'.44] 75-619271
Contents

Page

Introduction 1

Materials and Methods 1

Natural History and Ecology 2

Web-Site Constancy 2

Stabilimentum Construction 5

Egg Cocoons 6

Predation on Spider Eggs 7

Development of the Young Spiders: Changes in Size and Color 7

Insect Associates o£ Nephila maculata 12

Birds and Nephila Webs 16

Behavior 16

Courtship and Mating 16

Thermoregulatory Behavior 20

Spiders as Human Food 20

Conclusion 21

Literature Cited 22

The Ecology and Behavior of

Nephila maculata: A Supplement

Michael H. Robinson

and Barbara Robinson

Introduction

In 1970-1971 we carried out an investigation into

the ecology and behavior of the giant wood spider,

Nephila maculata, at Wau, Morobe District, Papua

New Guinea (Robinson and Robinson 1973a).1 We

subsequently made related studies on the golden

web spider, N. clavipes, in Panama (Robinson and

Robinson 1973b, 1974). These studies of Nephila

species, taken together, represent a very considerable accumulation of information on the natural

history, ecology, and behavior of this conspicuous,

ubiquitous, and ecologically important group of

tropical spiders. When we returned to Papua New

Guinea in 1974 we were again confronted by N.

maculata in great abundance and were stimulated

into making further studies of the biology of this

magnificent species. This new work extends and

amplifies our previous studies. In addition to reporting on the new investigations, we here also

examine the phenomenon of web-site constancy

(and its relationship to both predatory success and

levels of kleptoparasite infestation) using data that

we collected in 1970-1971. The most important of

1

 Since we refer to this work throughout the paper, we

have avoided conventional circumlocutions and simply cite

it as "(1973a)" unless indicated otherwise.

Michael H. Robinson and Barbara Robinson, Smithsonian

Tropical Research Institute, Post Office Box 2072, Balboa,

Canal Zone, Panama.

the new investigations was a largely biometrical

study of the life history of the species, a neglected

aspect of araneid biology. This revealed marked

differences in the developmental histories of the

two sexes. Although the new data are from diverse

aspects of the biology of the giant wood spider, we

feel it is better to present them together, disconnected as they may be, rather than in a number of

separate reports. The subjects covered are listed in

the "Contents."

Materials and Methods

The spiders were studied in the Wau Valley,

Morobe District, New Guinea, at a number of

localities but principally in the grounds of the Wau

Ecology Institute. Descriptions of the principal

study area and of the spider are given in Robinson

and Robinson (1973a). The data on web-site constancy are extracted from data gathered during the

day-by-day census of the prey caught by a sample

population of 10 adult female N. maculata that was

carried out during 1970-1971. Details of this census

and the broad climatic conditions that obtained at

the time are given as cited above. All the other new

data presented in this paper, except for the life

history studies, result from observation and experimentation involving techniques similar to those

used in the main study. The methods used in the

life history studies are described separately in the

appropriate section below.

1
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Natural History and Ecology

WEB-SITE CONSTANCY

Over the years of our spider studies we have

formed the impression that spiders may move from

sites where they are catching an abundance of food

(Robinson and Olazarri, 1971). To test whether this

was true we decided to analyze the ancillary data

that we collected during our studies of the prey of

N. maculata, when we also noted the frequency

of web-site changes (and distance moved, when

known), the frequency of absences associated with

egg-laying, and whether or not the spider returned

from these absences to the same web (or moved).

Additionally we counted the number of kleptoparasites associated with each sample spider once

a week, not daily as erroneously stated in Robinson

and Robinson (1973a:29). (This error arose during

transcription of field notes when one of us assumed

that the other had recorded weekly totals, whereas

the figures for kleptoparasites were the result of a

one day per week census. Thus the figure for the

average number of kleptoparasites is really 5.7 and

not 0.92 as stated on page 29 of our 1973 paper.

The latter figure was obtained by dividing the

census total of 2978 kleptoparasites by the total

number of spider days during the census—3237.

This incorrect calculation seriously underestimates

the average. The total should have been divided by

520—representing 10 webs on 52 census occasions.

The statement on page 30 of our 1973 paper that

the maximum number of kleptoparasites present on

any web on one day was 15 is incorrect and an error

arising from the same process of confounding. It

was, in fact, 30.)

Returning to the original data, we have examined this to determine whether there are any correlations between moving from a web site and previous levels of prey capture, egg-laying, and numbers

of associated kleptoparasites. We have also been

able to categorize all the moves for the distance

involved. Finally we have been able to compare

the number of kleptoparasites present on the web

before and after a move. The latter analysis is of

particular interest since Robinson and Olazarri

(1971:35) suggested that the orb-web spider Argiope

argentata (Fabricius) could possibly reduce the

burden of kleptoparasites by moving its web from

time to time.

Several points emerge immediately from this

analysis. Adult female N. maculata operate their

webs at the same site for quite long periods. On

average they stay in one place for at least 12 days

and may stay for very much longer. In Figure 1 we

have plotted the time distribution of intervals between one move and the next. This illustrates two

things. Once having moved, the spider may make

a number of moves before settling down and will

then remain in one place for a considerable period.

This is what one would predict if the spider were

moving so as to find a good prey capture site.

Despite this tendency, there is also a tendency

for the spider to move after an egg-laying excursion.

Forty-three percent of all the moves that we recorded occurred after the spider had quit the web

to lay eggs, and these spiders did not return to the

old web but relocated their webs. This type of

move is probably not occasioned by lack of predatory success at the old site since in these cases we

saw the spider get fatter and fatter until it was able

to lay eggs (after which it was always dramatically thinner). Furthermore, when we analyze the

weight of food captured in the two clear weeks

before egg-laying, we find that this is well above

the weekly average for the year (see below). If a

postovipositional move is not a response to low

predatory success it needs explanation. There are

at least two possibilities. The spider could move

simply because it was unable to find its old web

after moving some distance away to spin its egg

cocoon. The fact that the female does return to her

web after 16.8 percent of known egg-laying excursions (15 out of 89) is not conclusive one way or

the other since the difficulty of finding the web

again may vary according to the distance she travels

away from it before she lays her eggs. A further

possibility is that the spider moves away from her

egg-laying site as an antipredator or antiparasite

response. The presence of a large web close to an

egg mass could be a useful clue to both predators

and parasites. Certainly a large mass of nutrient-rich

eggs is attractive to some predators (see later) and

we have found dipteran larvae in N. maculata egg

cocoons. If the move were a defensive response the

spider should, perhaps, take down its web before

the egg-laying excursion. It does not, thereby leaving at least 200 calories of valuable silk behind

(calculated from Lubin, 1973:353) in addition to a

possible egg-site marker for predators and parasites.
NUMBER 218

50—

= 231

< 1 1-2 2-3 3-U

weeks

4-5 5-6 6-7 7-8

FIGURE 1.—Time intervals between one move and the next. Note that in this diagram we

have included deaths and disappearances since these terminate a stay at one site. In the

case of disappearance ("gone" in the graphs), we either failed to find the spider or found

it in an inaccessible location.

(Certainly the web deteriorates quite rapidly and

may become an insignificant remnant of silk long

before the eggs hatch, but it is not possible to

assess whether it might then still serve as a clue

to the presence of the adjacent eggs.)

Those moves not associated with egg-laying are

of considerable interest since in a sense they are

"pure" moves. Egg-laying moves as discussed above

could be the fortuitous result of the spider being

unable to find its web after an absence. This cannot

be the case with this second category of moves.

These could be a simple response to poor prey cap

ture at a given site, or a means of getting rid of

kleptoparasites, or function to reduce the possibility

of predation (the longer the spider remains at one

site, the greater the risk of some predator finding

it?), or they could be multifunctional. The lack of

predatory success hypothesis can be tested if we

can make an assessment of what constitutes a sufficient input of food for an adult female N. maculata. Since our data are for dry weight of prey remains, we need a figure for baseline predatory

success based in these terms (Robinson and Robinson, 1973a: 32, convert from dry weight of prey

remains to the weight of the original prey by assuming that the remains represent around 20 percent of the original wet weight). We have two bases

for such an estimate. The first is to use the average

weekly catch calculated from the year's total catch

for the 10 sample spiders. This works out at 0.267

grams, as follows:

Total dry weight of prey remains for year 123.544 grams

Number of spider days 3237

Average dry wt. prey remains/per day/per spider =

* % - -»•» -

Average dry wt. prey remains/per week/per spider = 0.0382

X 7 = 0.267

Basic data from Robinson and Robinson, 1973a.

How useful such an average is cannot really be

judged at our present state of knowledge; 8 of the

10 spiders sampled have averaged weekly catches

that are lower than this bulk average.
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

As a second basis for estimating a baseline for

predatory success, we have taken the prey captures

for the two weeks preceding egg-laying wherever

no move occurred during these two weeks. (In making this estimate we exclude the week in which the

egg-laying actually occurred.) This procedure results

in a calculated average of 0.306 grams, arrived at

as follows:

Total dry wt. prey remains for wks. preceding egg-laying as

defined above 43.432 grams

Number of weeks involved 142

43.432

Average dry wt./per week/per spider = ^ = 0.306

Matching the weight of prey caught in the week

prior to the "pure" moves against these two baseline estimates, we get the following results:

Total number of moves not associated with egg-laying but

preceded by an uninterrupted week at web site* 49

Number preceded by a week of 0.267 grams prey remains =

20 = 40.8%

Number preceded by a week of 0.306 grams prey remains =

13 = 26.5%

• Moves were only scored if they were preceded by an

uninterrupted week since we were using one week's score

as a criterion of success.

We feel that these results are a good basis for

assuming that spiders will move from web sites that

are good for prey captures and that such moves do

not function to enhance prey capture efficiency, but

have another function. (It can be objected that our

criterion of a good week is wrong, or that it is

unrealistic, since the spider almost certainly does

not use the weight of prey caught in a week to

determine whether or not it is doing well at a

particular site. At the present we can only guess

at the possible mechanisms involved but would

doubt whether, if the spider does assess its predatory success, it does so on a day-to-day basis. To do

so would mean that a spider might respond to a

period of poor prey captures occasioned by bad

weather as though it were due to an unsatisfactory

web site.)

Returning to our original hypothesis, that moving periodically may reduce the kleptoparasitic load

on the spider, we can test this by seeing whether

this is actually the case. Out of the 20 moves made

by spiders obtaining 0.267 grams of prey or more:

15 resulted in a reduction of kleptoparasites;

4 occurred when the spider had no kleptoparasites to start

with and none immediately following the move;

1 resulted in an increase of kleptoparasites (but we noted

that this spider moved into a web site that had been

vacated by another spider two days before).

Of the 15 moves that resulted in a reduction of

kleptoparasites, most resulted in a substantial reduction, as the following before-and-after couplets

show: 7-4, 4-0, 10-1, 11-2, 5-2, 9-0, 22-0, 8-5, 9-0,

12-4, 4-0, 16-0, 15-3, 9-2, 3-0.

The fact that the spider moves its web site even

when it has no kleptoparasites associated with it

does not mean that the function of moving is not

related to kleptoparasite reduction. The simplest

mechanism for ridding a web of kleptoparasites

might simply be to move from time to time irrespective of the actual numbers present. The possibility

that moving from a good prey capture site is an

antipredator or antiparasite strategy cannot be ignored, but even if this is the correct functional

explanation we must conclude that moving incidentally reduces kleptoparasite numbers.

The distance the spider moves is of interest. In

Figure 2 we have plotted distances moved for all

the cases where we have reasonably accurate data.

In some of the long moves we may have missed

intermediate web sites, i.e., when the spider was

found after two or three days it could have moved

in stages to a new site, but, if so, it probably did

not build webs en route or we would have found

these. Note that a considerable number of moves

are over 1.5 meters and many are over 3 meters.

Enders (1974) reported that araneid spiders will

interfere with the use of space by competitors by

moving onto one another's webs. This "invasion"

sometimes results in supplanting a resident spider

but most of Ender's data (1974:320) refer to cases

where the owner of the web was absent (due to the

observer's interference). In one of the cases of

supplanting (out of 8 observed?, the data are not

clear), the supplanting spider left a good web site

to move into a poor one. At the abandoned web

site the spider had taken 29 prey in 13 days, whereas

it moved to a site where only one prey was taken in

the same period. Although the occupation of a

vacant web site or web cannot be regarded as competition, the behavior of invading any web site

could result in competitive interference if it caused

abandonment of an occupied web or web site. In

our 5487 observations on marked N. maculata fe-
NUMBER 218

50

162

0-1-5 1-6-3 3-1-45 46-6

meters

6-1-75 76-9 9-1-10-5 106-12 12-1-13-5

FIGURE 2.—Distances moved from one web site to the next. (The data for this graph are smaller

than those presented in Figure 1 because we only recorded distances moved when we found the

spider within a day or two after a move.)

males (we had 10 "reserves" marked as well as the

10 sample spiders), we never recorded supplanting.

We have two records of adult female N. maculata

feeding on subadult female N. maculata which

clearly could have resulted from unsuccessful "invasions" on the part of the latter. We have, additionally, one record of a spider moving into a web

site shortly after it was vacated, but no record of a

successful supplanting of an occupying female (this

would have been very evident if it had occurred).

We conclude that if competitive interference occurs

in N. maculata it does not occur sufficiently often

(amongst adults) to account for moves that are not

occasioned by poor prey capture results or egglaying. Ender's (1974) account does not make it

clear whether "invasions" occur mainly between

members of the same age class or whether they

occur at restricted periods in the spider's seasonal

cycle. This makes assessment of the possible significance of this phenomenon difficult.

STABILIMENTUM CONSTRUCTION

In our previous report we noted that N. maculata

occasionally builds a more or less perpendicular

linear stabilimentum. This was the first record of

stabilimentum building by species of the genus

Nephila, and we noted that such stabilimenta were

built by immature individuals and that we had not

recorded them from the webs of adults (Robinson

and Robinson, 1973a: 8). We subsequently discovered that N. clavipes builds similar stabilimenta

and that these too are confined to juveniles (Robinson and Robinson, 1973b). In addition, it turned

out that these stabilimenta were almost entirely

confined to molting webs (i.e., those consisting of

frame, radii, and no viscid spiral). In our observations on N. maculata webs with stabilimenta we

failed to note whether these were entire functional

webs or molting webs. We can now state that N.

maculata builds stabilimenta in molting webs in

the same way as N. clavipes and although we have

no quantified data we would guess that a stabilimentum is found in molting webs of individuals

(females) from about the eighth instar onward (see

later for instar sizes). We believe that the spider

molts in its web because this places it above ground,

isolated from surrounding vegetation, and out of

reach of some predators. It also is protected by

the barrier web (s) when molting, but needs a very

secure platform where it can harden after emergence from its old cuticle. Omitting the viscid

spiral from a molting platform makes sense since

the process of molting might otherwise be interrupted by prey becoming entangled in the web and

shaking the spider at a vital moment. (Molting in
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

0 cm

FIGURE 3.—The egg sac (also called cocoon) of Nephila maculata. The outer basketwork

of silk strands is sufficiently transparent to allow the egg mass to be seen within.

N. madagascariensis is beautifully described and

illustrated in Bonnet, 1929; our observations on

molting in N. maculata, N. clavipes, and N. fenestrata accord fully with his.) We have speculated

elsewhere (Robinson and Robinson, 1973b) on the

function of these rarely built stabilimenta. We can

add that we have also seen stabilimenta in the molting webs of N. fenestrata in Nigeria and Natal

(Republic of South Africa).

EGG COCOONS

In our previous paper we did not describe the

egg cocoons of N. maculata nor give data on the

number and weight of their contents. We here

rectify this omission. Figure 3 shows a typical egg

sac of N. maculata. (Note that these are concealed

beneath vegetation and less well camouflaged by

color than those of most Argiope species which are

often attached, in the open, to the frame members

of the web.) Bonnet (1930a:70-72, fig. 11) describes

the cocoon of JV. madagascariensis and also the

process of egg-laying and cocoon construction. We

have not seen Ar. maculata build an egg sac, but,

allowing for the crudity of Bonnet's illustration, we

assume that the egg sacs of the two species are essentially similar. (The cocoons of N. clavipes that we

have examined in Panama certainly have the same

general structure.) We believe that the structure

of araneid egg sacs may give some clues to the relationships within the family and are currently gathering data on this subject. Nephila egg sacs are

more closely similar to those of Gasteracantha species than they are to those of Argiope. They differ

from those of the latter genus in having the eggs

surrounded by an open, semitransparent "basketwork" layer of silk rather than a dense, opaque,

multilayered "fabric" of silk that is typical of

Argiope species.

The Nephila cocoons that we have examined

contain considerably more eggs than those of other

araneids that we have so far dissected and those

of N. maculata are also considerably heavier.

Sample of 10 cocoons (judged to be within one

week of laying):

Average number of eggs 2469

Range 2080-2900

Average weight of eggs 1.219 grams

Range 0.980-1.450

Average weight of silk in cocoon 0.091 grams

Range 0.070-0.110

Bonnet (1930a: 74) gives details of the number of

eggs in successive cocoons of two female N. madagascariensis. The largest numbers were 1351 and
NUMBER 218

1023 respectively; he gives no weights. The number

of eggs in the egg sacs of N. maculata is much

higher than we have found in any of the other

araneid species that we have studied so far. The

weight of eggs is very considerable and may amount

to anything from a quarter upward of the weight

of an adult spider. The eggs are presumably the

main constituent contributing to the tastiness of

N. maculata as a food item for humans. The loss

of this much body weight and bulk explains why

adult females are so conspicuously thin when they

return from egg-laying (Robinson and Robinson,

1973a: 13).

PREDATION ON SPIDER EGGS

During our recent stay at Wau we kept a number of araneids in large screened cages to obtain

egg cases of known age and origin (the three large

Argiope species at Wau have similar egg cocoons).

After the spiders laid we marked the egg cases and

left them in situ, examining them daily to determine development times. On two occasions holes

appeared in the nylon screen walls of the insectaries

and several egg cocoons that we had tacked to the

frame of the cages disappeared. We assumed that

the holes had been made by rodents that had eaten

the egg cases. Livetrapping within the cages yielded

two specimens of an arboreal rat Melomys rufescens.

This rat climbs well and is sometimes caught in

traps baited with commercial dogfood (Robinson

and Robinson, in preparation). A Nephila egg cocoon must constitute a good energy package for

this animal. In their normal site the egg sacs would

be accessible to a light, climbing rodent.

DEVELOPMENT OF THE YOUNG SPIDERS:

CHANGES IN SIZE AND COLOR

There have been few studies of the life histories

of spiders. Levy (1970) reviewed the then available

literature and published a list of 31 species (from

18 families) for which some details of the life history were known. In most cases, the minimum

details known were the number of molts in the

development of the two sexes. Only two araneids

seem to have been studied. Of these, one is N.

madagascariensis (Bonnet, 1929, 1930a) and the

other Araneus diadematus (Bonnet, 1930b). In his

study of N. madagascariensis, Bonnet raised the

spider in captivity at Toulouse, France, starting

with eggs received from Madagascar (Malagasy Republic). He measured the size of each instar and

recorded the time spent at each developmental

stage. We felt that a life history study of the larger

N. maculata would be of interest, but could not

afford the time to raise the spider from egg to adult,

in captivity. However, during April and May 1974,

we noticed that immature specimens of N. maculata

were extremely abundant at several sites in the Wau

valley and decided to try to work out the stages

and sizes in the life history by using a large collection as a basis for biometry. We collected a starting

sample of immature spiders that seemed to cover

a wide range of sizes and measured these after they

had been killed in alcohol and then transferred to

water. We assume that shrinkage due to dehydration was much less than it would have been if we

had used specimens preserved in alcohol. Specimens

large enough to be measured without the microscope were measured against a steel ruler. Smaller

specimens were measured in water under a stereobinocular microscope using a millimeter scale

graticule. Early sampling measurements permitted

us to segregate the spiderlings into discrete classes

and we then measured individuals until we had 10

in each size class. By this method we were eventually able to construct a schematic life history.

We measured the length and width of the cephalothorax, the length and width of the abdomen,

and the total length of legs I and IV. In measuring

legs we always measured the longest one of the pair,

assuming that the shorter one may have been regenerated after being autotomized at a previous

stage (hence short). Abdomen measurements yield

the most variable results as this is the most elastic

part of the spider's body and even in the middle

instars is capable of becoming considerably enlarged

during the period between the molts. In addition

to measuring the spiderlings and immatures, we

also noted the dorsal color pattern of the cephalothorax and abdomen and any conspicuous markings

on the legs. We chose to monitor changes in dorsal

coloration, rather than ventral, since this seemed

to change most radically during development and

is usually more visible in the field. We were able

to distinguish males from females at least three

instars before they became adult by using pedipalpal characteristics.

The possibility of a confusing overlap in dimen-
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

5 0 -

100-

50-

leg length

mm

N. maculata 0

d

o N. madagascar.

i i i r i I

2 3 4 5 6 7

I F i r i i I

8 9 10 11 12 13 14

instar

FIGURE 4.—Increase in lengths of legs I + IV for Nephila maculata and N. madagascariemis

(see text). (Solid circles = Ar. maculata females, rings = males; open circles = N. madagascariemis both sexes.)
NUMBER 218

sions occurred only in the very smallest instars and

here the leg measurements were critical since they

provided an unequivocal means of separating instars. We could not decide whether some very large

specimens were adult females or whether they were

penultimate instars. To determine this, we kept

some in large cages and were able to observe molting. In this way we confirmed the existence of

instars 12, 13, and 14, about which there could

have been some doubt (see later).

Allowing for an instar and molt in the egg case,

after eclosion but before the rupture of the egg

sac wall (see Valerio, 1974, for the basis for this

designation), there are a possible 13 molts and 14

instars in the development of the adult female.

Males, on the other hand, undergo at the most

seven molts and adults represent an eighth instar.

The comparisons with Bonnet's (1929) results with

cage-raised N. madagascariensis are most interesting.

He found that females of that species reached maturity after the 11th molt. (30.5%), or the 12th molt

(56.5%) or some even after the 13th molt. 13%).

We did not dissect the large specimens categorized

as 12th, 13th, and adult instars, but as mentioned

above, captive 12th and 13th instars were seen to

molt. This does not mean that some individuals do

not reach sexual maturity at their 11th and 12th

molts. They may, but we are not able to detect

any external evidence of this.

Males reached maturity at the 8 th instar and we

found no 7th instar-sized males that had adult

pedipalps. Interestingly, the molt from pre-adult

male to adult is accompanied by a conspicuous

reduction in body length. This does not seem to

have been noted by Bonnet (1929) in the case of

N. madagascariensis. We have noted a similar phenomenon in males of several Argiope species.

The sizes of the various instars are given in Table

1, alongside the available measurements for N.

madagascariensis from Bonnet (1929:317, 318 and

pi. 1, where we were able to measure off dimensions

not given in the text). It is remarkable that there

is considerable correspondence between the measurements we obtained from wild-caught specimens

and those that Bonnet obtained from cage-reared

specimens of a different species. This correspondence is the more remarkable because the measurements were made in two different ways. We

measured the length of the first and fourth legs

separately, unaware that Bonnet had used the

length from the extremity of the first leg on the left

side to the extremity of the fourth leg on the right

side. The combined lengths shown in the table for

N. maculata were obtained by simply adding the

mean lengths of the two legs. Bonnet's system of

measurement should produce slightly larger figures

because it would include a section of cephalothorax,

since he measured from left appendage to right

appendage. We have graphed (Figure 4) the increase in leg I + IV length with developmental

stage for the two species.

Apart from the increase in size shown on the

graph, there are changes in the coloration of the

body and the legs and changes in the '"gaiter" on

the distal portions of the tibiae of legs I, II, and IV.

These gaiters of dense stiff hairs first appear at the

sixth instar and become prominent at the seventh

(fig. 1, p. 3, of Robinson and Robinson, 1973a,

shows a seventh instar female N. maculata). The

adult female has no gaiters.

The changes in general coloration are shown in

Figure 5. The second instar spiderling is largely

unpigmented and the patterning of the dorsal surfaces first appears after the second molt. Then the

dorsal surface of the abdomen becomes striped and

the dark stripes on a light ground persist until the

ninth molt when the abdomen becomes slatey in

color and ultimately is almost black. The patterning on the ninth instar represents a clear transition

between the striped juvenile coloration and the

adult coloration: the stripes are much reduced and

a large area of the surface is slatey bronze. As we

noted in our previous study (Robinson and Robinson, 1973a:2-3), the species retains some striping as

an adult in other parts of its range. The striped

Japanese form (Yaginuma, 1968, pi. 29: fig. 162)

has a pattern closely corresponding to that of an

eighth instar New Guinea N. maculata, i.e., compared to the spiders in New Guinea it retains a

juvenile color pattern. (We have seen the species

in small numbers in Northern Territories, Australia, near Darwin, where its color form as an

adult is similar to the New Guinea specimens. The

specimen that we saw in Singapore was also all

dark. However, in India (Borivili near Bombay)

and Sri Lanka (various localities), all adults were

striped.) The coloration of the spider's legs changes

from a translucent gray in instars three to six to a

banded pattern in at least some individuals of instars seven and eight and is then replaced by the
10

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

TABLE 1.—Biometrical details of the development of N. maculata

compared with N. madagascariensis

Body part (measured in mm)

Cephalothorax length

Cephalothorax width

Abdomen length

Abdomen width

Leg I

Leg IV

2 I + IV

Body length

N. madagascariensis (from Bonnet 1929; see text)

S I + IV

Body length

N. maculata

2 I + IV

Body length

Body part (measured in mm)

Cephalothorax length

Cephalothorax width

Abdomen length

Abdomen width

Leg I

Leg IV

2 I + IV

Body length

N. madagascariensis

(from Bonnet 1929; see text)

2 I + IV

Body length

N. maculata

2 I + IV

Body length

Instar number"

2 3 4 5 6 7

0.5 0.5 0.8 1.2 1.6 2.0

0.4-0.6" 0.4-0.6 0.7-0.9 1.0-1.3 1.5-1.9 1.9-2.3

0.4 0.5 0.6 1.0 1.3 1.6

0.3-0.45 0.4-0.6 0.5-0.8 0.8-1.1 1.0-1.4 1.4-1.8

0.8 1.0 1.2 2.2 3.2 4.0

0.7-0.85 0.9-1.1 1.0-1.7 1.5-3.0 2.5-3.6 3.4-4.8

0.5 0.6 0.8 1.0 1.2 1.5

0.4-0.7 0.5-0.8 0.7-0.9 0.8-1.1 1.0-1.4 1.3-1.6

2.1 3.0 4.7 8.0 10.8 15.0

2.0-2.2 2.8-3.1 4.2-5.5 7.0-9.0 10.0-11.7 13.9-18.0

1.8 2.3 3.7 6.2 8.2 10.9

1.6-1.9 2.1-2.4 3.1-4.3 5.0-7.0 7.3-9.0 10.0-13.5

3.9 5.3 8.4 14.2 19.0 25.9

1.3 1.5 2.0 3.4 4.8 6.0

5.0 7.0 10.0 13.8' 19.5' 27.5'

<1.0 2.0 2.4 3.2 4.7 7.0

3.9 5.3 8.4 14.2 19.0 25.9

(18.8) * (24.0)e

1.3 1.5 2.0 3.4 4.8 6.0

(5.4) • (7.6) •

Instar number * Adult

8 9 10 11 12 13 14

2.8 4.1 5.7 7.6 9.0 10.2 14.1

2.5-3.0 3.3-4.8 5.0-6.8 6.7-8.8 7.5-10.0 9.7-11.0 12.0-15.1

2.1 3.1 4.4 5.8 7.6 7.8 10.1

2.0-2.3 2.5-3.8 4.1-5.1 5.0-6.2 6.0-7.9 7.2-8.0 10.0-10.2

6.8 9.7 12.5 16.6 18.8 20.8 28.0

6.0-7.5 7.0-13.0 11.0-15.0 12.0-20.0 15.5-23.0 18.0-24.0 26.0-35.0

2.0 3.0 4.0 5.5 6.9 7.5 10.2

1.9-25 2.1-3.8 3.0-5.0 4.0-7.5 5.0-8.0 6.1-9.0 9.0-15.0

21.0 31.2 43.2 52.0 62.4 72.8 86.0

18.0-26.1 28.2-36.0 39.0-47.8 50.2-55.0 59.0-65.5 68.0-80.0 79.0-92.0

17.1 25.9 35.8 44.0 52.4 61.1 70.5

16.0-20.0 22.0-31.0 30.4-39.0 41.0-46.0 46.0-55.0 51.6-65.0 68.0-74.0

38.1 57.1 79.0 96.0 114.8 133.9 156.5

9.6 13.8 18.2 24.2 27.8 31.0 42.1

38.0 50.6 67.4 91.7d 116.8d 129.0d

10.0 13.0 19.0 26.0 34.0 34.0

38.1 57.1 79.0 96.0 114.8 133.9 156.5

(34.0) •

9.6 13.8 18.2 24.2 27.8 31.0 42.1

(6.3) •

• No measurements made in instar 1 (egg cocoon).

b

 Range in mm.

1

 Some adult males.

d

 Some adult females.

e

 Males in parantheses.
NUMBER 218 11

-10 mm.

10-14

0

FIGURE 5.—The dorsal coloration of immature stages of JV. maculala. (Black = black or dark

brown coloration, white = pale grey on abdomen and silvery color on thorax except for instars

10-14, which includes adult, where the bulk of the adbomen is shown white but is dark slate

gray to almost black. The coloration of the adult male is not shown. Instar 8 = an immature

female.)
12 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

adult color pattern of black legs with bright yellow

areas on the underside of the femora at their apices.

The significance of the color changes is by no

means clear nor is there any obvious functional

explanation for the differences in adult coloration

between the New Guinea forms and those in Japan,

India, and Sri Lanka. Striping may be good obliterative (disruptive) camouflage for the early stages

in development since many of the early stage

spiderlings build their small webs down in the

herb layer where there is a background patterning

of vertical lines. As the web becomes larger and

more prominent, camouflage—or any form of concealment—may become impossible and camouflage

patterning valueless. It is interesting to note that

N. madagascariensis retains a complex patterning

of the dorsal surface into the adult stage (Bonnet,

1929, pi. 2).

We did not record the details of changes in the

ventral patterning of the abdomen during development, but from the study of photographs (that

were taken for other reasons but incidentally record

the color patterns of the ventral abdomen) can

state that they are minor compared with the

changes in dorsal coloration. The general yellow

spotting of the juvenile forms remains on the adult

but is less prominent. The broad yellow bar associated with the epigyne region (Robinson and

Robinson, 1973a, fig. 1) is also prominent in the

adult (see Figure 6).

Levy (1970) has discussed the life cycles of spiders

in relation to the development rates of the two

sexes and has concluded that spider life cycles fall

into two basic classes. There are spiders (the majority?) in which the developmental rates of the

two sexes are the same (and they mature at the

same time) and others in which males mature long

before females. Although we have no data on the

time it takes male N. maculata to mature, we now

know that they mature after a maximum of seven

molts at a tiny fraction of the weight of an adult

female. Unless they have some means of delaying

the final molt and remaining at the web-building

seventh instar stage for long periods, they must

become mature around about the time females of

the same generation are also in their eighth instar

(given roughly equivalent growth rates and assuming an average rate of predatory success). Once

adult, the males cease building webs and presumably subsist on food reserves and occasional commensalism with females. We think that it is

extremely improbable that male N. maculata are,

in these circumstances, substantially more longlived than males of N. madagascariensis. Bonnet

(1929:509) states that the life of the male in the

adult state is very short ("La vie des $ [sic] a

l'etat adulte est fort courte") from 1 to 2 months.

If this is so there seems little chance of siblings

mating.

Deevey (1949) reported a very strong influence

of food supply on the number of molts that Latrodectus mactans underwent before reaching maturity. Clearly we have no means of assessing the

possible influence of this factor on our results.

However, we would guess that the presence of large

numbers of immature spiderlings, at any time, is

likely to reflect favorable conditions for survival

and development. For this reason, and because our

larger species has only one molt more than N.

madagascariensis, we suspect that our data reflect

the results of reasonably "normal" 'conditions of

development.

INSECT ASSOCIATES OF Nephila maculata

During the year of our earlier study (April 1970-

April 1971) we recorded the presence of a pyralid

moth resting on the webs of the sample population

of adult female N. maculata on over 30 occasions.

The moth was Hurculanea sp.2 (Pyralidae: Pyralinea). Figure 7 shows it resting on a web element in

a typical head-down posture. The moths assumed

such resting postures, by day, only on the upper

structural members of the web or the associated

barrier web (frame threads, foundation threads,

mooring threads, and barrier web threads, see

Robinson and Olazarri (1971) for comparison of

U.S. and British terminology). The threads on

which the moths rested were nonviscid and always

horizontal or near horizontal; we did not find them

on sharply inclined threads. At rest the moth assumed a delta-shaped attitude with the forewings

completely covering the body outline and the antennae apposed to the body and concealed. The

moth hangs from the spider's silk supported by the

hind legs whose tarsal claws grip the line. These

2

 Identified by D. Ferguson, National Museum of Natural

History, Smithsonian Institution, Washington, D.C., to whom

we are most grateful.
NUMBER 218 13

FIGURE 6.—Photograph of the ventral surface of an adult female showing the spotting and

longitudinal pale lines. (This photograph also shows a male in copula with right embolus

inserted and left pedipalp raised.)
14

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 7.—Moth of Hurculanea sp. resting on a web element of a N. maculata web, head-down

and ventral surface toward the camera. (Note the position of the two legs III that are holding

the silk.)

legs are extended in the plane of the wings, beneath

them, and one leg may be extended asymmetrically

as shown in Figure 7.

During our first visit to New Guinea we failed

to find Hurculanea on the webs of araneids other

than Nephila, but we have since found several

specimens associated with the webs of Argiope

reinwardti (Doleschall). We believe that the association between this moth and araneid spiders is not

fortuitous and raises interesting questions about its

function, mechanism, and evolutionary origins. In

its resting attitude, the moth has most of its typical

insect structures concealed either by attitude (legs,

antennae) or color and structure (head and wings).

Both the dorsal and ventral surfaces of the body

have camouflage markings. The insect is generally
NUMBER 218 15

similar to the irregularly shaped pieces of leaves

and other plant debris that accumulate in and on

Nephila webs within the forest. The moth is probably protected by a relatively unspecialized form

of special protective resemblance (plant-part mimicry). However, adopting a resting attitude on

spiders' web must involve the insect in fairly complex background selection and settling behavior (see

later) and we would expect it to confer some additional advantage over resting, in a similar manner,

on vegetataion. It could be that resting in a position that is virtually isolated from nearby substrates

protects the moth from the large numbers of predatory or omnivorous ants that constantly forage on

the surface of leaves, twigs, and stems in this district. Even if ants moved along the frame threads

of the web, and we have not seen them do this, the

moth might well be alerted to their approach by

the vibrations of the web silk. Pocock (1903) reported an instance of commensalism between a

social eresid spider and a microlepidopteran, Batracheda stegodyphobius Walsingham. He claimed

that the moths were sensitive to vibrations set up

by the spiders and actively escaped predation.

Despite the possibility that resting on a spider's

web is a defense against ants or other ambulant

predators, we are inclined to believe that it is a

defense against predation by birds. We believe that

the strong webs of araneids are hazards to birds

and are avoided by them where possible. If this is

so, then a camouflaged insect that associated with

spiders' webs would have camouflage as a primary

defense and the deterrent presence of the web as a

secondary defense (for discussion of the concepts

of primary and secondary defense see Robinson

1968, 1969, and Edmunds, 1974). The evidence for

the idea that araneid webs may constitute a hazard

to birds is derived from two sources: records of bird

captures by spiders and direct observations. McKeown (1936:154-173) lists a large number of Australian araneids, including Nephila spp., catching

and consuming birds. He even quotes (page 165)

a report of a bird avoiding a spider's web by drastic

evasive action. Our own observations (detailed separately below) show that when a naive bird flies

through a spider's web the experience can have a

lasting effect in producing a strong aversive response. If this hypothesis is correct, we would predict that Hurculanea species will not be found

associated with spiders that build ephemeral and

weak webs (e.g., the four species of Gasteracantha

found in the same area).

The question of how the moth detects the presence of, and alights upon, the appropriate web element is an interesting one. At first sight it would

seem to imply a complex discrimination and a complex maneuver. We were unable to observe this

process: moths released by day in a large insectary

containing Nephila webs settled indiscriminately.

Presumably they make a background selection at

dawn and, after initially settling, only exhibit escape responses. Experiments on background selection by cryptic moths have been conducted in

confined quarters and the result (rather than the

process of selection) has been the object of study

(Sargent, 1966, 1969a, 1969b). We have observed a

large nematoceran (Diptera) settling on the webs

of various cribellate spiders in the Wau area. In

this case the insect flew in bobbing flight, with its

long legs extended forward of the almost vertically

oriented body, until a web member was touched,

then the insect settled instantly. The fly looked

as though it was aware the web was nearby before

it actually touched it. Moths, as lepidopterans, may

be preadapted to alight on spiders' webs in two

ways. First, we have observations that suggest that

butterflies may be able to see and avoid spiders'

webs in some circumstances, and the compound eyes

of most nocturnal moths seem to be as relatively

large as those of butterflies. Second, because of

their loose wing scales, they are less likely to become

stuck to spiders' webs than most other insects

(Eisner, Alsop, and Ettershank, 1964). They may

thus be able to see the lines of the web and alight

on them and, because of the loose wing scales, the

consequences of mistakes may be somewhat less

than they would be to a nonlepidopteran.

An alternative to alighting directly onto the silk

would be to alight on nearby vegetataion and move,

by walking, onto the framework of the web. Even

if the moth found itself on a lower web element, it

could walk upward to an upper frame member.

The moth runs some risk of being attacked by

the spider if it persists in moving after settling on

(or walking onto) a web member. Adult N. maculata will move onto frame members of the web, in

apparent predatory excursions, if a vibrating insect

is touched against these. However, as the spider

approaches a light motionless insect, it plucks and

the moth could use this as a cue to arrest movement
16 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

or escape by flight. The problem of alerting the

spider to its presence is probably not a major one.

A number of insects have solved this problem.

Emesinids (Hemiptera) are commonly seen moving

about the webs of araneids. Wygodzinsky (1966:

52-54) quotes observations on this problem and

notes that the insects do not seem to become entangled in the webs. He suggests that their longlegged gait may help them to move about the web

(presumably by reducing potential points of contact to the tiny area of the tarsi). The nymphs of

all emisinids, and the adults of some species are

apterous and they must be capable of locating webs

and walking onto the webs from adjoining substrates.

Stages in the evolution of resting on the silk lines

of a spider's web can be envisaged as follows:

1. A cryptic moth that is a crude leaf-mimic rests

hanging from leaves and twigs supported by two

legs only.

2. Because webs occur in the understory where

this cryptic moth rests, it is only a small behavioral

step from resting on a narrow leaf edge to resting

on a narrow silk line. Moths that have this aberrant behavior are at the selective advantage over

those resting on vegetation because of their association with a hazard to aerial predators.

BIRDS AND Nephila WEBS

On our second visit to New Guinea we handraised a number of insectivorous birds for use in

experiments on insect defensive adaptations. These

birds were raised on a diet of raw eggs, bread, and

milk, and confronted with a variety of insects when

they were several months old. We conducted experiments in a large experimental cage into which the

birds were admitted from their living cages. We

tested the palatability of various araneid spiders

and found that the birds—Butcher Birds (Craticus

cassicus) and Shrikes (Lanius schack)—would readily eat all the large common araneids, including

N. maculata, taking them live from the grass floor

of the experimental cage where we placed them. On

one occasion several N. maculata were left overnight in the experimental cage and one built a

web from the root of the cage close to the entrance

from the living cage housing five Butcher Birds.

When the birds were admitted to the experimental

cage, one bird flew straight out and through the

web. The effect was dramatic: the web broke, but

the bird was brought to earth fluttering as though

crippled. A section of web was adhering to the

upper surface of the bird's right wing, over the

elbow joint. This immobilized the joint sufficiently

to bring the bird down, and it spent several minutes in frantic preening activity before it finally

removed the sticky web material and hopped onto

a perch from which it was able to resume normal

exploratory behavior. For at least three weeks after

this incident the bird was reluctant to enter the

experimental cage and only did so after its cage

mates had done so. Since the birds were only given

insects (their favorite food) inside the experimental

cage we regard this aversive response as being an

intense one. No other birds ever flew into Nephila

webs in the experimental cage. This incident occurred, in all probability, because the spider had

fortuitously built close to the home cage exit and

the bird flew so rapidly through the door that it

had no time to avoid a novel hazard with which it

had had no previous experience. We think that this

observation reinforces the conclusion (above) that

large orb-webs may constitute a hazard to birds

and we would expect birds to quickly learn to

avoid webs.

Behavior

COURTSHIP AND MATING

Our previous study included details of the courtship and mating behavior of N. maculata and concentrated mainly on the complex behavior of the

male once it had moved onto the body of the female. We did not at that stage have information on

the approach of the male to the female during the

initial stages of courtship, nor did we look at interactions between males. We can now add some

details on these subjects. In addition, we have seen

more copulations and postcopulatory behavior and

must revise some of our previous descriptions.

MALE APPROACH.—There seem to be two possible categories of male movements on the web of

the female:

1. Initial movement onto the web and approach

to the female or to a waiting position.

2. Subsequent repeated approaches to the female

from a waiting position.

We distinguish these on a post hoc basis. We have
NUMBER 218 17

introduced males to various locations on the outer

perimeter of the female's web and watched their

movements. These movements are very different

from those of an "established" male that has been

"in residence" for sometime. We therefore describe

them separately.

Initial movements on the web are slow and the

spider walks with legs I more or less constantly

off the web, waving them in front of him and tapping the web lightly from time to time with one or

other tarsus I (this movement across the web is

very similar to that of courting males of Leucauge

papuana, Robinson and Robinson, in prep.). At

this stage the female may detect the presence of

the male and pluck the radii, at which moment the

male will freeze or even drop off the web in an

escape movement. Figure 8 plots the approach

movements of three males approximately to scale.

Some idea of the hesitant slowness of this approach

can be gained from the fact that it took male A 3

minutes 52 seconds to move from his starting point

to point X. After 27 minutes all three of these

males had assumed head-down postures above the

hub and were then intermittently making approaches to the female. This pattern of hesitant

initial approach occurred whenever we introduced

a male onto a female's web. We assume that males

arriving naturally behave in a similar way but have

never seen this happen. Most frequently we find

webs in which the males are "resident," having assumed waiting positions somewhere above the hub.

Males in residence face down the web and make

the second type of movement in direct approaches

to the female. The initial movement onto the web

and into a waiting site must be one that entails

considerable risk. Any movements of the female

are likely to result in the males making escape

responses (dropping off the web on their dragline).

We have seen two males that were moving up the

web respond to a female predatory excursion by

simultaneously dropping off the web. Once the

males have reached a position above the hub they

are much less "nervous." This may be because they

are much less at risk in this relatively neutral3

part of the web, or could result from the fact that

in their approach they have somehow gauged the

aThe area above the hub is without viscid spiral in some

Nephila species, and in N. maculata it has a poorly developed and small, viscid, spiral zone (Robinson and Robinson,

1973a:8).

state of the web-owner. The latter explanation

seems improbable since N. maculata males will

move onto the webs of immature females that are

unlikely to be sexually receptive and tolerant of

males; perhaps the male's apparently cautious a p

proach is exactly that and not a series of signals to

the female. (We have one record of a male N.

maculata moving onto the web of an adult female

Argiope aemula, where he eventually assumed a

waiting stance and subsequently visited the female

at the hub before moving off. He was not attacked.)

Approaches to the female may be numerous, of

short duration, and made on either surface of the

web. The male may walk slowly with legs I off the

web as in the initial approach, but more frequently

the waving of legs I is merely intermittent. However, the approach to the female is interspersed

with one or more bouts of on-the-spot jerking. In

this, the spider bobs up and down with all legs in

contact with the web. The effect of this must be to

transmit a fairly regular group of (burst of) vibrations to the female. As he approaches, the male

usually enters the V made by the two legs IV of the

female and may bounce, on the spot, in that area.

During this kind of approach the male may lightly

touch the female's fourth legs and the apex of the

abdomen. Figure 9 shows the movement of the

male—lightly touching the female on the abdominal apex. He immediately retreats if she moves and

often retreats after merely touching the female once

or twice. Ultimately such approaches are followed

by the male moving onto the body of the female

and commencing the silk deposition activity that we

described in detail in our previous paper (Robinson and Robinson, 1973a:36, 38, 41).

INTERACTIONS OF MALES.—Males interact at all

stages of approach and courtship. When males are

at the "resident" approach stage, described above,

a male down at the female resting place will orient

toward an approaching rival and move out to contact distance. When two males meet in this manner,

they touch legs (I and II) and from this stage may

go on to fight, or one may simply retreat, leaving

the victor to approach the female. We have seen a

number of these encounters and have the impression that size is not decisive in determining the

outcome. The subject is susceptible to quantification and we think that it would repay further study

(we would guess that a small, highly motivated,

male could drive off a larger, less highly motivated,
18 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

FIGURE 8.—Movements of three males (1, 2, 3) across the

female's web. (Solid circles = sites of pauses, or rests, in the

approach. Open stars = points from which the males lept

off the web, and solid lines = paths of males dropping after

jumping off the web; in one case, male 3 drifted laterally

during the drop. The position X is referred to in the text.)
NUMBER 218 19

FIGURE 9.—Male Nephila maculata (M) gently touching the apex of the female's abdomen (F).

(The inset shows the movements of the male's first left leg (1, 2, 3) during this activity (traced

from frames of 8 mm film about 6 frames apart, filmed at 18 frames per second).)
20 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

rival). Males that have moved onto the female and

commenced the prolonged direct stage of courtship

seem to be interrupted less frequently than those

at the approach stage, but such interruptions do

occur and we saw one case of complete supercession.

The male was displaced after at least one hour and

25 minutes on the female and one copulation (he

had probably been there for a much longer period).

The intruding male came down the web to the

female, touched her right leg IV very briefly and

then moved straight onto the abdomen; the male

in possession jumped straight off the female to 20

cm below the hub. Note that a succession of males

will mate with a female and aggressive interactions

between them can determine, if anything, mainly

the order of copulation. (There is a further possibility. We suppose that the female must eventually

stop accepting males and intermale aggression may,

therefore, actually prevent some males from mating.)

COURTSHIP.—Our further observations confirm

the details of direct courtship given in our earlier

paper and we have seen further instances of "opportunistic" mating in which the male copulated with

a newly ecdysed female. Two new observations are

of interest: we have found that males continue

courtship into the night and have seen the female

catch and kill a courting male. The males courting

during the night were seen on a web (built on the

side of a house) that was dimly illuminated by light

from a window, so that we cannot say that the

phenomenon occurs under natural conditions, but

see no reason why it should not. The first and only

example of the female seizing and killing a male

came during a session in which the female had been

courted and copulated with by a succession of

males. Our observations on this female extended,

with numerous breaks, from 10:30 AM to 10:40 PM

(nightfall at 6:15 PM). After the second observed

copulation of the day, male number 4 moved onto

the female, went immediately to the epigyne, and

without preliminaries attempted an insertion. The

female bent at the waist, pushed the male forward

to the jaws with legs I and II and bit him for 30-40

seconds. The male was then picked up in the tarsi

of legs I and flicked away from the web with the

typical leg movements used in discarding prey remnants after feeding or in the removal of an inedible

item from the web (our field notes are somewhat

less than objective—"lovely contemptuous rejection

movements"). One hour and twenty minutes after

this incident another male was in copula with this

female.

COPULATION.—Our recent observations on copulation in N. maculata make it evident that we made

an erroneous assumption in our previous report

and that other observers have made a similar mistake. We reported that copulations were brief and

that though "such brief insertions may represent

unsuccessful attempts" (Robinson and Robinson,

1973a:41) we imply that insertions of over a minute

are normal. These were all we saw during our

previous study. During our second study, we saw

several very long insertions and have seen long

insertions in three other species of Nephila and

would guess that these are a regular feature of

Nephila mating. We timed the following copulations: 12 minutes, 35+ minutes, 13 minutes, 21i/2

minutes, 121/4 minutes, 68 minutes, 48 minutes, 15

minutes. We think that short insertions may be

typical of the stages leading up to long insertions

and we simply missed the latter (due to confounding and impatience) during our previous study.

None of the copulations that we saw ended in the

female attacking the male, he simply withdrew and

moved on to other activity.

THERMOREGULATORY BEHAVIOR

In our previous study we reported that N. maculata oriented itself in such a way as to minimize

heat absorption when the sun was shining through

the web (Robinson and Robinson, 1973a:64-65

and fig. 30). We subsequently discovered this and

other postures in the behavioral repertory of N.

clavipes in Panama (Robinson and Robinson,

1974). Our report of the thermoregulatory behavior

of N. clavipes details the thermoregulatory postures

that enable it to minimize heat absorption irrespective of the orientation of its web. We here report

that M. maculata has an equally extensive repertory

of thermoregulatory postures and shows no tendency to orient its webs normal to the direction of

maximum insolation.

Spiders as Human Food

Bristowe (1932:392-393) reported that in Siam

(?present-day Thailand) N. maculata is eaten as

food, raw or roasted. The flavor, with salt, is said

to be similar to raw potato and lettuce mixed. New
NUMBER 218 21

Guineans from several areas of the Central Highlands eat araneid spiders, particularly N. maculata,

which is large and often plentiful, and Crytophora

moluccensis, which is fairly large and occurs in colonies (and so may be easy to collect in large numbers). Nephila maculata are collected alive and

placed in the hollow of a bamboo stem 3"-4" in

diameter and 18" long. During collecting, the open

end of the bamboo is stoppered with a piece of

folded banana leaf. Eventually, when sufficient fat

adult females are obtained, the stoppered stem is

put in the embers of a fire and left there for 10-15

minutes until the green bamboo is blackened. The

spiders "split their skins" during the cooking process. They are then eaten, either entire (legs and

all) or the abdomen is nipped off and the rest discarded. We ate several and found the flavor good

and the texture in no way repugnant. Descriptions

of food flavors always involve comparisons with

familiar foods and can be misleading. Inevitably

a fire-roasted food item has a smoky flavor predominant, but we both agree that N. maculata has also

a nutty flavor (M.H.R. compares it to peanut butter without the objectionable consistency). We both

ate spiders that were packed with eggs. Nephila

maculata (adult females) must be a good source of

palatable protein in an area where protein sources

are scarce. Gravid females weigh 3 grams or over

and are, at times, abundant; they must be useful

occasional food.

Conclusion

No synthetic summary is possible for a study

that encompassed a number of disparate elements

in the biology of a large invertebrate. We think

that biological studies lose an essential element

when they cease to be inductive and that the types

of questions raised by aspects of this essentially

supplemental study are worth pursuing further. For

instance, the question of the ecological role of

changing web sites is critical to our understanding

of much of araneid biology, and the adaptive significance of various types of life history strategies are

a potentially fertile area for further study. As we

press further with studies of tropical spiders, we

come to agree more and more with Robinson and

Olazarri (1971:35) that "the problems seem limitless and the spiders remain an intellectual challenge."
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U.S. GOVERNMENT PRINTING OFFICE: 1976 21t-33»/»

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