United States

Department of

Agriculture

mm

j Combined Forest Ftest

fic^Sm Research and

(^^ ^

Development Program

Agriculture Handbook

No. 534

Gypsy Moth

Handbook

Predators

of the

Gypsy Moth

o

c=-o aer- -

:33:ä. 5»-C~ yíi '_- "—-ia-^^

me. .r-^'^'O aKcT 35» „.-.-^

! - I

Will F^î*:--:

f-ri '.„

r- •* ;—!*_, :x3

8-

—«I

¿¿cz

^o -< ^

CT = -X!

<•) i-rs
Contents

In 1974 the US. Department of

Agriculture initiated the Combined

Forest Pest Research and

Development Program, an

interagency effort that

concentrated on the Douglas-fir

tussock moth in the West, on the

southern pine beetle in the South,

and on the gypsy moth in the

Northeast. The work reported in

this publication was funded in

whole or in part by the program.

This manual is one in a series on

the gypsy moth.

Introduction 2

Understanding Prédation 3

Life history of the gypsy

moth

3

Gypsy moth behavior and

prédation

Role of predators in gypsy

moth control

6

9

Prédation and gypsy moth 10

population stability

Why natural control?

Prédation potential of birds

and mammals

10

12

Factors affecting predator

potential

Effect of defoliation on

13

16

gypsy moth predators

The Predators 17

Overview 17

Birds 17

Mammals 31

Amphibians, reptiles,

and fish

46

Invertebrate predators 51

Reexamining Our Wildlife 63

Perceptions

Conclusion 64

References 70
Predators of the Gypsy Moth

by

Harvey R. Smith and R. A.

Lautenschlager ^

Introduction

An all-out research effort by the

U.S. Department of Agriculture is

being made to find ways to control

the gypsy moth, Lymantria dispar

(L.), a major pest in the Northeast

that has defoliated as much as 2

million acres of forest and shade

trees in a year. Since its accidental

release in Massachusetts in 1869,

the gypsy moth has spread north

into Canada, south into West

Virginia, and west into Ohio. The

insect is most damaging as a larva

(caterpillar), when it feeds on leaves

from May to early July. Although

the gypsy moth prefers oaks, more

than 500 plant species are eaten by

this insect (Forbush and Fernald

1896, Mosher 1915).

The goal ofthe Expanded Gypsy

Moth Program is to develop and

select ecologically sound, practical

measures to manage the gypsy moth

and reduce its damage. Scientists

are currently developing an

integrated control system, a

program that uses a combination of

control measures in a selected area.

This system emphasizes the

biological control methods of

interrupting the gypsy moth's

reproductive cycle, spreading its

fatal diseases, exploiting its parasites

and predators, and using safer,

selective pesticides.

* Respectively, research biologist and

consulting wiJdlife biologist, Forest Service,

Northeastern Forest Experiment Station,

Hamden, Conn.
Understanding Prédation

Life History of the Gypsy Moth

An understanding of predators and

the associated components of

prédation is necessary to develop a

successful gypsy moth control

program. It is important to know

how the predators that kill gypsy

moths affect and are affected by the

other components of an integrated

control management system.

The goals of this booklet are to:

• Provide insight into the variety,

number, potential, and impact of

gypsy moth predators.

• Aid in the understanding of the

components of a predator/prey

system.

• Pave the way to understanding

the relationship of gypsy moth

prédation with prédation of other

northeastern forest insect pests.

• Help to develop an appreciation

for the intricacies of the forest

ecosystem.

Like all butterflies and moths, the

gypsy moth has four distinct life

stages: egg, larva, pupa, and adult

(figs. 1-3). In the Northeastern

United States gypsy moth eggs

usually hatch around the first of

May. The young larvae grow

rapidly; males molt four times and

females five times. The stages

between these molts are called

instars. First-instar larvae climb

trees to feed on tender, spring

foliage, and to spin silken threads,

from which they hang and are then

blown by the wind to other areas.

Larvae remain on or near foliage

until they have molted twice (third

instar). In the fourth instar a

behavioral change occurs, and the

insects descend from the tree

crowns each day at dawn to rest in

the litter around the base ofthe host

tree or under flaps of loose bark.

Larvae leave these resting places at

dusk to return to the tree crowns to

feed. In sparse populations this daily

migration continues for 2 to 3 weeks

until the larvae are fully grown (fifth

instar for males, sixth for females).

Most of the gypsy moth larvae will

pupate in this same daytime resting

location. However, when gypsy

moth densities are high, older larvae

remain on the foliage and feed day

and night, and pupation occurs

mainly on the trunks or under large

limbs of the host tree.
Figure 1.—Gypsy moth larva.

Figure 2.—Female (left) and

male gypsy moth pupae.

Figure 3.—Gypsy moth female

adult with egg mass.
Female gypsy moth larvae pass

through one more instar than males,

pupate about 1 week later, and are

larger than males. Both female and

male adult gypsy moths emerge

from their pupal cases in about 2

weeks. The adult female moth has

wings but rarely flies. She rests on a

tree, emitting a potent chemical

signal called a sex pheromone that

attracts male gypsy moths. After

mating, the female normally

deposits one egg mass containing

between 100 and 800 eggs. During

egg laying, hairs from the female's

abdomen are incorporated into the

egg mass to insulate the eggs.
Gypsy Moth Behavior and Prédation

The gypsy moth in North America

exhibits a defense behavior that

evolved in its native European

habitat—the migrating of larvae

from the tree crown to the litter at

the base of the host tree. Campbell

and Sloan (1976) suggested that this

behavior evolved to enable the

gypsy moth to evade natural

enemies (birds and parasites) that

w^ere active in the canopy. In North

America, however, this downward

migration increases the insect's

vulnerability to mammals and often

results in high gypsy moth mortality.

The gypsy moth has other defenses,

including stiff, prickly hairs and

warning coloration, both apparent

in the larval stage. Buckner (1966)

pointed out that there are few

vertebrate predators ofthe forest

tent caterpülar and the gypsy moth,

apparently because oftheir strong

defenses against prédation by

vertebrate predators.

These defense mechanisms may

have limited the number of gypsy

moth predators in North America,

but many predators do exist. Some

appear completely unaffected by

these defense mechanisms and

others have developed ways of

coping with or circumventing them.

For instance, small mammals often

attack gypsy moth larvae from the

underside, removing organs and

fluids, while leaving the larval skin

and the protective, prickly hairs

intact. Some birds that ingest the

larvae whole periodically shed and

regurgitate their stomach linings

that have become embedded with

the larval hairs (fig. 4).

The defense behavior of larvae

raises some interesting questions

about its effectiveness for survival

of the species. In this country birds

still seem an important regulatory

force (Campbell and Sloan 1977),

causing the gypsy moth larvae to

maintain their pattern of resting in

litter at the base of a tree. But is this

behavior really protective, since

larvae in litter are exposed to small

mammals? Are the larvae surviving

only to become prey in the pupal

stage?

Bess (1961) and Bess et al. (1947)

indicated that in moist forests, when

gypsy moths rest in the litter,

survival is low, and innocuous

populations exist. Campbell and

Sloan (1976, 1977) verified these

observations and presented further

evidence that vertebrates are

essential in maintaining low

populations. They estimated that

vertebrates killed 70 percent of the

pupae in a series of sparse, stable

populations and that white-footed

mice (Peromyscus) accounted for 40

percent of those removed. They

also showed that when birds and

small mammals were removed, the

insect populations could increase

tenfold in 1 year.

Gypsy moth larvae seeking a

daytime resting location often select

the dark tunnels of small mammals

located just below the litter. In a

sparse gypsy moth population in

Mashpee, Mass., which showed no

visible signs of defoliation, gypsy

moth larvae apparently favored

these small mammal tunnels as a

resting location (Paszek 1977). An
Animal and Hant Health Inspection

Service field crew collected within a

52-ha area approximately 8,000

female sixth-instar larvae, prepupae,

and pupae almost exclusively from

small mammal tunnels located at the

base of oak trees. Few pupae were

found anywhere else. This behavior

of resting and pupating in small

mammal tunnels is not unique and

has been observed in our study area

in Connecticut, but the fact that

gypsy moths used these tunnels

almost exclusively at pupation

locations seemed unusual. Small

mammal prédation was evident in

these tunnels by the large number of

pupal fragments found (Paszek

1977), raising the question of what is

the subsequent effect on survival in

these situations.

Figure 4.—Cuckoo stomach.
The role of small mammals as

predators of the gypsy moth in

Europe is not well known.

However, the effectiveness of

defense mechanisms that the gypsy

moth evolved in Europe may have

been lessened in northeastern

American forests because the

potential predators and habitats are

different.

We know of only one study dealing

with mammalian predators of the

gypsy moth in Europe—Rotschild

1958. He reported that the remains

of gypsy moth larvae and pupae

were found in the stomachs of

Apodemusflavicollis and A.

sylvaticus (Old World wood mice)

and Dyromys nitedula (the tree

dormouse) in the Soviet Union, and

that the stomachs of these mammals

were often filled exclusively with

the remains of these insects. These

European rodents, plus the smaller

Micromys sp. (the harvest mouse),

have characteristics that could make

them important gypsy moth

predators: All eat insects, and the

forest dormouse and the harvest

mouse are skillful climbers.

It is difficult, however, to draw any

conclusion about the role of

European mammals in gypsy moth

population dynamics. For example,

one American scientist who visited

the Soviet Union in 1975 was told

that Apodemus was not important in

regulating gypsy moth popuk-tions

(Lewis 1978).

AWhowgh Apodemus, Dyromys, and

Micromys may be gypsy moth

predators in Europe, only

Rotschild's (1958) paper indicates

that the first two are. In

northeastern American forests, we

have two common small mammals

that are important gypsy moth

predators: The white-footed mouse

and the shorttailed shrew {Blarina).

Both of these mammals readily eat

gypsy moths, and the white-footed

mouse commonly climbs trees to eat

larvae, pupae, and adult moths.

Although European forests contain

a variety of shrews, including

several Sorex sp. (longtailed shrews)

and Crocidura sp. (the whitetoothed shrew), there is no

equivalent ofthe North American

shorttailed shrew.

Habitat differences also influence

predator effectiveness. The long dry

summers typical of the south-central

European forests where gypsy

moths occur cause considerable

vegetation competition for the

available moisture. This situation

often results in forests composed of

overstory trees with more grasses

and fewer shrubs in the understory

(Smith 1978). This condition

provides poor habitat for the small

mammals that depend on dense

shrubs for both food and cover and

probably limits both the number and

diversity of small mammals that live

in these areas. Forests in the

Northeastern United States,

however, are quite moist and often

have well-developed shrub and herb

layers that offer both food and cover

to small mammals and birds.
Role of Predators in Gypsy Moth

Control

In each life stage, the gypsy moth

becomes prey and is part of the diet

of several animals, but until recently

the role of predators in gypsy moth

population dynamics was not well

documented. The predatory role of

birds received most of the attention

of early naturalists (Forbush and

Fernald 1896), who based their

findings on daytime observations.

Diurnal (daytime) birds were

considered to be the primary

predators offorest insects, and these

investigators seldom discussed

nocturnal mammals or mentioned

other vertebrates.

Birds were recognized as being

important in gypsy moth population

dynamics and as an instrument of

control over 80 years ago when

Forbush and Fernald (1896)

identified several species that ate

gypsy moths. The same study also

mentions amphibians, spiders, and

insects as predators; mammals,

however, are ignored (except

skunks, which are reported as

feeding on adult female moths).

Hamilton and Cook (1940)

emphasized that the beneficial role

of small mammals in the economy

of the forest had received little

attention. When Buckner (1966)

described the role of vertebrates in

biological control offorest insects,

the situation still had not changed

significantly. Bess et al. (1947) were

the first to suggest that small

mammals (mice and shrews) were

important predators of the gypsy

moth. Although more species of

birds have been identified as

predators of the gypsy moth in this

country, mammals may have a more

important impact on gypsy moth

populations. Gypsy moth

populations in Japan (Furuta 1976)

appear to be regulated by birds, but

in the United States, the roles of

birds and mammals appear uniquely

to complement each other

In the past 10 years considerable

knowledge of the predatory role of

birds and mammals has been

gained, and it is hoped that someday

forest managers will accept

vertebrates as an important

regulatory force and utilize that

knowledge in pest management

systems.
Prédation and Gypsy Moth

Population Stability

Why Natural Control?

Prédation, although a powerful

natural force that operates

simultaneously with other physical

and biotic forces such as climatic

catastrophes, habitat limitations,

food shortages, diseases, and

parasites, has limitations. Prédation

does not exert constant pressure

and as a suppress!ve force does not

reduce populations to levels as low

as those resulting from climatic

catastrophes, starvation, and

epizootics.

What is the relationship between

prédation and gypsy moth

population stability? This is difficult

to answer because the specific

causes leading to gypsy moth

outbreaks have not yet been

determined. We do know, however,

that in certain circumstances

predators are capable of maintaining

gypsy moth populations at harmless

levels for an indefinite period

(CampbeU 1975, CampbeU and

Sloan 1977), but it would be

inaccurate to say that prédation can

control gypsy moth populations or

prevent fiiture outbreaks.

Gypsy moth population densities do

respond to predator pressure, but

periods of low predatory pressure

alone do not necessarily cause an

outbreak. When low predatory

pressure coincides with other

population "releasing" mechanisms,

an outbreak is more likely to occur

Furthermore, during an outbreak,

prédation may seem insignificant

when other forces, such as disease,

are decimating gypsy moth

populations.

The gypsy moth has found an

ecological niche in this country and

is here to stay. What we must do

now is choose how we wish to live

with or control this insect:

• Do nothing and let nature take its

course.

• Continue to use pesticides on the

hot spots.

• Attempt an integrated control

management program that may

allow us to maintain low gypsy

moth populations.

The history of gypsy moth control

in this country has three stages.

First there was the mechanical era,

a seek-and-destroy approach, where

armies of men sought to eradicate

the insect with fire and creosote.

This approach resulted in only local

and temporary suppression of the

pest.

Then came the chemical era, the

pesticide approach, when millions of

acres of forest and woodland were

aeriaUy sprayed with DDT. Although

this direct kill approach provided

quick and decisive protection from

the insect, it was again only

temporary. The money and effort

expended on pesticides did not get

at the underlying causes of gypsy

moth outbreaks and did nothing to

prevent outbreaks from reoccurring.

Watt (1%8) stated that the aerial

application of pesticides, if timed

correctly, would save the foliage but

would not reduce the populations

during the following generation. He

believed that the main factors

determining generation-togeneration density were weather

and other density-dependent factors.

10
Brown (1961) demonstrated that

despite extensive spraying of DDT

over 600,000 acres in 1950, gypsy

moth populations rose in 1951.

The reason pesticides cannot keep

pace with forest insect pests

involves the basic biology of the

pest species. As Watt (1968) said,

"... through eons of natural

selection it has evolved homeostatic

capabilities to deal with

catastrophes so that insecticidal

treatment is merely one of a class of

events the species is adapted to

withstand."

The third stage, integrated control,

is an ecological approach to the

control of a pest insect. An

integrated control program

combines suitable control

techniques—^biological agents such

as pathogens, parasites, and

predators, habitat manipulation, and

chemicals—^in an ecologically

compatible way. A properly

executed integrated control system

should maintain pest populations

below levels of economic injury.

Smith (1%9) stated that integrated

control obtains uniqueness because

emphasis is put on the fullest

practical utilization of existing

mortality and suppressive factors in

the environment, and that strategy

is one of management and

containment rather than one of seek

and destroy.

For reasons of economy, and

because of concern about chemical

contamination, it would be wise to

control forest pests through

management of suppressive forces,

which are self-limiting and keep pest

species at low densities. To

successfully accomplish this goal it

is necessary to analyze natural

mortality factors and determine the

influence or impact of each factor

on the pest. Predators are one of the

most promising natural mortality

factors being considered.

The fundamental reasons why

biological controls could work have

been outlined by Watt (1%8):

'The affected, or doomed,

individuals are left in the population

after they have been committed to

die, or after they have been

committed to produce sterile

offspring. In this way, individuals

who are destined not to do the

population any good in the future

are still in the population, eating

food, taking up space, and in general

exerting competition pressure on

individuals who will survive the

treatment. In this situation, the

population of pests has the worst of

both worlds: it faces the same, or

almost the same, competition

pressure that there would be

without control, so no anticontrol

homeostatic mechanism is elicited,

yet at the same time the population

is being, or is about to be,

controlled."

11
Prédation Potential of Birds and

Mammals

Birds and mammals have been

recognized as important predators

of the gypsy moth for many years,

but it is only recently that we have

been able to begin to understand

and appreciate their precise roles

within sparse gypsy moth

populations.

Two major factors are unique to

birds and mammals that aUow them

to achieve such an economically

important impact potential: They

are warmblooded, and they have a

highly developed learning ability.

Because they are warmblooded they

have a high metabolic rate requiring

a tremendous amount of food just to

produce the energy necessary to

maintain a warm body temperature.

Additional food is required by birds

and mammals to have enough

energy to perform other activities

such as running, climbing, flying,

and reproduction. Adult birds may

eat one-third their weight per day,

and young birds often eat more than

one-half their weight per day

(Chapman 1968). One study of food

consumption by birds and mammals

in a 1,000-ha virgin forest in

Czechoslovakia indicated that the

total bird population consumed food

equaling about 25 percent of its

weight daily, and the mammal

community consumed the

equivalent of 20 percent of its

weight daily (Turcek 1952).

Those mammals most useful as

predators offorest insects—^mice,

shrews, and voles—eat weight

equivalents much greater than 20

percent of their own weight every

24 hours. Shrews have ravenous

appetites and are alleged to

consume their own weight

equivalent in food every day.

The other major factor is the degree

to which certain functions of the

brain are developed in these

vertebrates. Both birds and

mammals learn to search out places

where various foods are found,

concentrate their foraging in those

places, learn to avoid insect defense

mechanisms, and seek insects or

parts of insects that are most

palatable or desirable. For example,

the white-footed mouse prefers the

larger female pupae to the smaller

male pupae and, after catching moth

larvae, eats only a very small

portion of the insect. Hoarding, a

behavior associated with learning

and well developed in mammals, has

been demonstrated by shorttail

shrews, which often gather pupae

and carry them below ground to be

eaten later

By necessity to meet metabolic

demands, the activity patterns and

the inquisitive and opportunistic

behavior of birds and mammals

make them particularly adapted for

searching out and killing gypsy

moths. Although diets will vary

among forested areas, and impact

potential can be lessened by other

prey and food items, both birds and

mammals can have a significant

impact on gypsy moth populations.

12
Factors Affecting Predator Potential

Perhaps the key to the effectiveness

of bird and small mammal prédation

on sparse, stable gypsy moth

populations lies in the behavior of

the gypsy moth. The feeding

response of a predator to a prey

usually follows this pattern: At low

prey densities, a few or no prey are

attacked; at moderate prey

densities, a steep rise in prédation

occurs; at high prey densities,

prédation levels off. This pattern

would hold true for the gypsy moth

and its predators if the insects did

not migrate out of the canopy and

aggregate in lower resting locations

during the day. This prey behavior

creates a unique situation; instead of

the predator chasing the prey, the

prey (gypsy moth) comes to the

predator at dawn and dusk, when

the insect is visible and attracting

attention simply by moving and

when many vertebrate predators are

at their peak activity.

By aggregating under loose bark or

leaves in the litter, the insect is

found in predictable resting sites

that predators have learned are

rewarding when searched. The

predators are thus able to exert

much greater predatory pressure on

sparse gypsy moth populations,

which aggregate, than would be

expected on insect prey (at low

population densities) with a random

resting distribution.

Determining the predator potential

for any species is difficult because

of the variables involved.

Understanding the following

variables will help us to assess

predator potential:

• The abundance and availability of

the prey (prey density), or at what

prey density do predators recognize

the prey as a potential food and

start to search for it.

• The abundance and availability of

alternate foods (including other prey

items).

• The density of predators.

• The size of predators.

• The number and the timing of the

birth of the predators' young.

• Each predator's period of

residency and the size of its feeding

area.

• Each predator's willingness to eat

the prey and the life stages preferred

and eaten.

• Each predator's ability to capture

and consume the prey (prey

defenses, conspicuousness, size, and

palatability, and the same

characteristics of the alternative

food sources).

Predators normally do not search

for or prey on species that are rare

because these species are seldom

encountered. Even when a

preferred prey item becomes

available, the amount consumed

depends on the abundance and

availability of alternative foods

(Tinbergen 1%0).

13
Predator density is a major factor to

predator potential. For example, a

low-density predatory species that

eats many gypsy moths will not

have as great an impact on the prey

population as an abundant predator

that eats moderate amounts of the

insect. A predator's size is also

important. It is energetically

inefficient for large predators to feed

on small prey, except when the prey

populations are dense, but a small

predator may use a small prey

extensively whenever it is available.

Several experiments have been

conducted with caged mammals in

order to better understand predator

potential. The history of one

experiment and two observations

from natural situations will help to

illustrate several factors that affect

predator potential.

In the experiment, six adult male

white-footed mice were individually

caged with 100 fifth-instar gypsy

moth larvae and water. Two of these

mice also received mouse chow (a

dried laboratory food), and two

others received mouse chow and

sunflower seeds. Mice given no

alternative food ate 98 percent of

the larvae, mice with mouse chow

ate 57 percent of the larvae, and

mice with mouse chow and

sunflower seeds ate 23 percent of

the larvae. The effect these

alternative foods had on the

percentage of larvae eaten after 48

hours clearly demonstrates the

selective feeding ability of the mice

and appears to be similar to what

happens in the wild—^the number of

prey eaten depends on the

availability of alternative foods.

A natural situation that illustrates

the effects of alternative food, the

defense mechanism of stiff hairs,

and prey density on gypsy moth

survival was recently observed in

New Lisbon, N.J. (Garlo 1977). Nest

boxes were placed on a 0.7-ha site

as part of a small mammal study. In

early summer 1976, while checking

the nest boxes for small mammals, it

became apparent that gypsy moth

larvae were using the nest boxes for

resting sites and white-footed mice

were using the same boxes for

nesting. Not only were predator and

prey living together, but the gypsy

moth larvae had a high survival rate

and adults laid egg masses in the

boxes.

14
Although all the nest boxes were

being used by mice, mouse density

was low (10 mice per hectare). In

addition to low mouse density, the

key to gypsy moth survival

appeared to be the abundance of

cankerworms, a hairless larvae

whose availability coincided with

that of gypsy moth larvae. In

laboratory feeding studies mice have

demonstrated a definite preference

for hairless larvae; mice in the wild

also prefer hairless cankerworms to

gypsy moths. This preference was a

definite factor in the high gypsy

moth survival rate.

By 1977, however, the situation in

New Jersey had changed. Mouse

density had increased to 35 per

hectare, and the alternative food,

cankerworms, had disappeared.

Gypsy moth density remained

essentially the same, and the larvae

continued to rest in the nest boxes,

but few gypsy moth larvae survived.

The absence of the cankerworms

and the increased mouse density

created more competition for food,

which resulted in a low gypsy moth

survival rate.

Another example of availability and

abundance influencing gypsy moth

prédation occurred in central

Pennsylvania in 1975. In early

summer gypsy moth larvae began

migrating from the tree crown at a

time when the litter and ground had

dried because of limited

precipitation and increased sunlight

reaching the forest floor through the

partially defoliated canopy. This in

turn caused earthworms and other

soil invertebrates to move deeper

into the soil, making them

unavailable as a food source. In this

situation robins were forced to

change their diet and eat large

quantities of gypsy moth larvae

when they became available on or

near the ground.

15
Effect of Defoliation on Gypsy Moth

Predators

One factor unique to predators of

defoliating insects is the effect of

defoliation on predators. Each

predatory species chooses a habitat

that meets its need for food and

cover. However, an infestation of

gypsy moths that results in near or

complete defoliation destroys the

protective cover and causes

unfavorable changes in the

microclimate within the defoliated

area. Many species of birds nest

near the ground (DeGraaf et al.

1975), and most small mammals live

on the ground in a forest. During the

day in a severely defoliated forest,

the temperature, especially near the

ground, increases dramatically, and

humidity drops. As species are

subjected to extremes in

temperature and humidity that they

are either unwilling or unable to

tolerate, and possibly increased

prédation because cover has been

diminished, they leave the area.

In 1975 in central Pennsylvania, the

population of yellowthroats, a

warbler species that prefers brushy

habitats, was approximately seven

times greater on the lightly

defoliated plots than on plots that

were severely defoliated; the

population of redback voles, small

mammals that are active day and

night, dropped dramatically on

severely defoliated plots; the

population of white-footed mice

continued to increase on all plots

(Lautenschlager et al. 1978). The

effect of defoliation was clearly less

on the nocturnal mice than on the

voles, which were forced during the

day to cope with increased ground

temperatures and/or possibly with

avian prédation.

Because these conditions occur only

at very high gypsy moth densities, a

time when predators are having little

or no effect, it is doubtful if the loss

of some predators would have any

effect on subsequent gypsy moth

populations. In most cases predators

leave the area only for a short time.

If refoliation occurs, many predators

will return within 2 to 3 months. If

major changes occur in stand

composition because of defoliation

and subsequent tree mortality, and

food and cover are affected,

significant changes could occur in

both the density and the number of

predatory species. These changes

could last for several years, and the

new predator community might be

more or less effective than the one

present before the changes

occurred.

16
The Predators

Overview Birds

Many species of animals in the

Northeast eat forest-defoliating

insects, which include the gypsy

moth. Some of these predators eat

only one life stage of the gypsy

moth; others eat two or more.

Although the emphasis of research

has been on birds and mammals,

some observations have been made

of prédation by amphibians, reptiles,

fish, and several invertebrates.

Within each predator group are

some species that are more

important as predators than others.

However, every predator is viewed

as part of the predator community,

with each having a part in the

collective impact of prédation on

sparse gypsy moth populations. It

cannot be assumed that all the

gypsy moth predators have been

identified, and it must be realized

that the roles of those identified will

change as the factors that affect

predator potential change.

When the total predator community

is working together it can maintain

gypsy moth populations at harmless

levels for an indefinite time. Birds

are a major part of the predator

community and play an important

role in reducing gypsy moth

populations.

Birds occur in every habitat type,

from nearly open areas to thick

brush and mature forests. Within

these habitat types they occupy

every available stratum, from the

forest floor to the top of the canopy.

During the breeding season and in

good habitats, birds reach

population levels of 5-10 pairs per

hectare. Our research in central

Pennsylvania indicated

approximately 7 breeding pairs per

hectare; Holmes and Sturges (1975)

in New Hampshire showed roughly

10 pairs per hectare; and Hamilton

and Cook (1940) in New York State

indicated approximately 5 pairs per

hectare. Therefore, during the

breeding season, a good woodland

songbird habitat probably supports

between 10 and 20 adult birds per

hectare.

Many species of birds move to

northern areas to raise their young

in the spring and early summer,

producing two broods of four to six

young each. During the time of

mating and raising of the young,

most birds need a diet high in

protein, and insects are eaten

extensively (Welty 1%2). Even

species that normally do not eat

large amounts of insects often

become seasonal insectivores.

17
Unfortunately, most observations of

birds eating gypsy moths have been

made when gypsy moth populations

were near or at outbreak levels, a

time when prédation has no

significant impact on gypsy moth

populations. From observation and

from what is known of the history,

behavior, and predator potential of

each species (Forbush and Fernald

1896, Galipeau 1975, Palmer and

Fowler 1975), birds can be placed in

one of two groups: Those species

that eat gypsy moths regardless of

the gypsy moth density (these

species would be particularly useful

in maintaining sparse gypsy moth

populations), and those species that

are attracted to high-density gypsy

moth areas because of the

availability of an abundant food

source (these species would

normally have little or no impact on

gypsy moth populations at low

densities).

Bird species in the first group

include the black-capped chickadee,

blue jay, red-eyed vireo, rufoussided towhee, scarlet tanager,

northern oriole, catbird, and robin.

These species are common residents

and eat gypsy moths when the

insect is at low population densities.

Birds species in the second group

include the yellow-billed and blackbilled cuckoos, common crow,

chipping sparrow, starling, common

grackle, red-winged blackbird, and

cowbird. The species in the first

group are more likely to encounter

gypsy moths at low population

levels and therefore are more likely

to eat them, but birds in the second

group will eat gypsy moths from

sparse populations if the moths are

encountered.

Many bird species besides those just

listed eat gypsy moths. Forbush and

Fernald (1896) listed 38 bird species

seen eating one or more life stages

of the gypsy moth. Many migrating

warblers, which often nest farther

north, often pass through gypsy

moth infested areas when the larvae

are still small. At resting stops

during migration these warblers

contribute to the collective impact

of bird prédation on low-density

gypsy moth populations.

18
Birds Useful in Maintaining Sparse Gypsy

Moth Populations

Black-Capped Chicliadee (Parus atricapiUus)

The chickadee (fig. 5) is a small

(about 11 g), common, wide-ranging

species that eats all life stages of the

gypsy moth, including the eggs. The

chickadee, normally found in forests

and along forest edges, has two

broods of approximately six young

per brood per year. The chickadee is

important because of the high

population densities it often reaches,

its activity pattern (foraging from

ground level to the lower canopy),

and its willingness to eat all life

stages of the gypsy moth. These

birds swallow small larvae whole

but must tear apart the larger larvae

to eat the preferred parts. The

chickadee has been seen catching

adult male moths resting on foliage

or tree trunks and then flying to a

branch with the insect in its mouth,

breaking off and discarding the

wings, and swallowing the rest of

the insect.

Figure 5.—Black-capped

chickadee.

19
Blue Jay (Cyanocitta cristata)

The blue jay (fig. 6) is a common,

large (about 85 g), wide-ranging bird

found in woodlands and along forest

edges. A pair of blue jays will

normally raise two broods of four to

six young per brood per year. Both

young and adult blue jays eat large

quantities of gypsy moth larvae

when the insects are available. They

have been observed moving from

branch to branch eating larvae,

pupae, and adults. Blue jays do not

eat all the larvae they kill;

sometimes larvae are simply killed

and then dropped to the ground.

In 1977 on Cape Cod, Mass., blue

jays demonstrated an interesting

behavior for catching adult male

gypsy moths (ODell 1977). Shortly

after sunrise the jays would begin to

search systematically the lower

branches and tree trunks for adult

moths resting there. The captured

moths were swallowed whole. By

midmorning, the jays would then

exhibit a behavioral change—^they

searched the shrubs for adult moths

resting on the underside of the

foliage. The blue jays soon learned

that these moths could be easily

flushed by hitting the shrubs and

became quite proficient at flying

into the shrubs, flushing the resting

moths, and capturing the insects in

flight.

Figure 6.—Blue jay.

20
Rufous-Sided Towhee (Pipilo erythrophthalmus)

The towhee (fig. 7) is an important

predator of the gypsy moth because

of its willingness to eat late-stage

larvae and adult moths. The towhee

is also important because of its large

size (about 40 g) and the high

population densities it often

reaches—up to two adults per

hectare in most early successional

forests where there is a large

amount of brush cover near the

ground. Under ideal conditions the

species may reach densities of two

to three times that of other bird

species in the same area. Towhees

normally raise two broods of four to

six young per brood per year.

Towhees feed mainly on the ground

but search for and capture gypsy

moths in sparse gypsy moth

populations whenever the gypsy

moths migrate to the litter. By

consistently consuming late-stage

larvae, pupae, and adults, the

towhee assists in maintaining sparse

gypsy moth populations.

Figure 7.—Rufous-sided towhee.

21
Red-Eyed Vireo (Vireo oliváceas)

The red-eyed vireo is seldom seen

but often heard singing from the tre^e

tops. It weighs about 18 g and is

found in many habitat types in the

Northeast, from forests to more

open areas. In prime habitats, the

red-eyed vireo may reach population

densities of two to five per hectare;

this bird normally has two broods of

four young per brood per year. Redeyed vireos forage in the canopy

and definitely contribute to the

mortality of young gypsy moth

larvae. They have been observed

eating all life stages of the gypsy

moth except eggs and, like the

chickadee, often swallow smaller

larvae whole. The vireo will place a

larger larva on a branch, tear it to

pieces, and eat selected parts.

Because the bird feeds mainly in the

canopy and consumes many earlystage gypsy moth larvae, it helps to

reduce populations of the gypsy

moth before the insects have a

chance to cause significant

defoliation.

Catbird (Dumetella carolinensis)

The catbird is commonly found

along shrub edges where these areas

meet more open areas. It nests and

feeds close to the ground in dense

cover and has been seen taking

larvae of all sizes and pupae to its

young. The catbird weighs

approximately 40 g and may have

three broods of up to five young per

brood per year. The catbird

normally forages in areas from the

litter to the lower canopy, so its

major impact is on late-stage gypsy

moth larvae, pupae, and adults.

22
Scarlet Tanager (Piranga olivácea)

The beautiful scarlet tanager (fig. 8)

is a useful gypsy moth predator.

Although this species never reaches

extremely high population densities

(approximately one pair per 2 to 8

ha), this bird is found in most

forests and along forest edges,

including yards which are bordered

by woodland. The scarlet tanager

may weigh as much as 30 g and

normally has one brood of four

young per year. It readily takes

many gypsy moth larvae from the

branches in the canopy. The tanager

eats all stages of the gypsy moth

except eggs. The majority of the

tanager's prédation, however,

occurs during the early stages of the

gypsy moth's life cycle, when larvae

remain in the canopy during the day.

The scarlet tanager reduces the

amount of defoliation by eating

many larvae before they have a

chance to eat large amounts of

foliage.

Figure 8.—Scarlet tanager.

23
Northern Oriole (Icterus gálbula)

The northern oriole (fig. 9),

commonly called the Baltimore

oriole, is useful in combating many

forest insect pests. Orioles are found

in the canopy along edges of lawns,

roads, fields, and ponds wherever

the edges blend into more mature

forests, including suburban yards.

Along these edges hang their

intricately woven nests. Orioles

weigh approximately 35 g and may

have one or two broods of four

young per brood per year. The

oriole is well known for its ability to

kill hairy caterpillars, like the

eastern forest tent and gypsy moth

caterpillars. This bird also eats

gypsy moth pupae and adults. Like

other birds that feed in the canopy,

the oriole starts to eat gypsy moths

when they are small larvae, before

they have a chance to consume

large amounts of foliage.

Figure 9.—Northern oriole.

24
Robin (Turdus migratorius)

The robin {fig. 10) is familiar to

almost everyone and is commonly

found along forest edges and in

urban, suburban, and rural yards.

The robin weighs approximately

80 g and often raises two or three

broods of four young per brood per

year. Although the robin lives in

forests, it never reaches high

population densities away from

natural or manmade openings. The

robin eats larvae, pupae, and adult

gypsy moths; depending on their

abundance, this insect may become

an important part of the robin's diet.

Although robins are usually pictured

pulling worms from the lawn, they

also forage in trees, removing larvae

and pupae. They have also been

observed picking up gypsy moth

larvae from dirt roads in

Pennslyvania. The robin probably

has its greatest impact on gypsy

moth populations when the ground

is dry and earthworms are not

readily available, because at that

time the bird must search for other

food.

Figure 10.—Robin.

25
Figure 11.—Black-billed cuckoo.

26
Birds Attracted to High-Density

Gypsy Moth Populations

Cuckoos iÇoccyTUs sp.)

The cuckoos (both black-billed, fig.

11, and yellow-billed) are normally

the first on a list of bird predators of

gypsy moth. However, because they

are uncommon away from a gypsy

moth outbreak, they have little

impact on maintaining sparse

populations. Cuckoos live in forests

and along forest edges, are large

birds (approximately 65 g), and may

raise two broods of four young per

brood per year. Cuckoos prefer latestage gypsy moth larvae, which they

also feed to their young. As soon as

the young can fly, small family

groups of cuckoos can be seen

eating gypsy moth larvae and pupae

in infested areas.

Common Crow (Corvus brachyrhynchos)

The crow, although very wary and

often hard to observe, is known to

eat large amounts of insects,

including late-stage gypsy moth

larvae, pupae, and adults. Crows

have often been observed searching

for larvae and pupae in infested

areas and removing loose, dead bark

from trees to reach larvae

aggregated there. Crows search for

food in most habitats, have

extensive home ranges, and travel a

considerable distance to utilize an

available food source. Their travels

often include visits to areas with a

high gypsy moth density, when latestage larvae and pupae are available.

They often return with their young

to feed in these areas.

In areas with moderately dense to

dense gypsy moth populations in

central Pennsylvania, crows started

to arrive when gypsy moth larvae

were in the fourth instar and were

seldom seen after the moths had laid

their eggs. Crows often raise two

broods of up to six young per brood

per year. Nestling crows require

large amounts of food and are often

fed late-stage gypsy moth larvae,

pupae, and adults when abundant.

However, even when gypsy moth

populations are sparse, they may be

eaten if encountered.

27
Common Grackle (Quiscalus quiscula)

The grackle (fig. 12) is commonly

found along forest edges, especially

around farms, where it often flocks

with other blackbirds. The grackle

eats all life stages of the gypsy moth

except the eggs. The grackle is a

large bird (about 115 g) and

normally raises one brood of five

young per year. The grackle's diet

consists of about 30 percent animal

matter, normally in preparation for

and during raising of the young,

which coincides with gypsy moth

abundance. Crackles have been

reported to flock to infested areas to

eat gypsy moths (Campbell 1975).

These birds may be important

predators within sparse gypsy moth

populations, when they eat moths

along forest margins, close to open

fields, and on farmlands. The

grackle does not, however, appear

to eat large numbers of gypsy moths

at these low densities, when the

gypsy moths are not abundant

enough to attract its attention.

Figure 12.—Common grackle.

28
Chipping Sparrow {Spizella passerína)

The chipping sparrow normally

inhabits forest edges, often nesting

in evergreens, and also is very

common around suburban homes

where there are open country and

brush edges. The sparrow may have

two broods offour young per brood

per year. The chipping sparrow,

although it normally feeds on seeds,

does eat many insects, including

gypsy moth larvae (small and large)

and adults. Although it is not big

(about 14 g), it may have some

impact on gypsy moth populations

by feeding on larvae found near the

ground.

Starling {Stumus vulgaris)

Since their introduction in 1890,

little good has been said about the

common starling. These birds are

normally found around urban and

suburban areas and eat large

amounts of gypsy moth larvae,

pupae, and adults when they

become available. Because starlings

are large (about 85 g) and often raise

three broods of five young per

brood per year, they consume large

amounts of food. The starling is an

opportunistic feeder and feeds on

the ground as well as high in the

canopy, depending on where food is

available. Although starlings seldom

venture far from human habitation,

they are probably useful in

destroying large numbers of gypsy

moths in areas with medium-high

densities.

29
Red-Winged Blackbird {Agelaius

phoeniceus)

The red-winged blackbird (fig. 13)

normally nests along swamp edges

and marshes but will also live in the

high grass along the edges of inland

meadows if wet areas are nearby.

This blackbird weighs

approximately 70 g and may raise

two broods offour young per brood

per year. When gypsy moths

become available, they may form a

significant portion of the blackbird's

diet because it eats both larvae and

adults. During the breeding season,

the bird's diet is mainly insects; in

areas where the birds are plentiful,

or where roving bands of first-year

males congregate, they probably

have some impact on gypsy moth

populations.

Figure 13.—Red-winged blackbird.

Brown-Headed Cowbird (Molothrus atar)

Cowbirds lay their eggs in the nests

of other birds, leaving the incubation

and raising of young to other

species. This permits the cowbird to

forage wherever food is plentiful.

Although associated with open

fields and farm animals, this bird is

also found in forests, where it eats

gypsy moth larvae, pupae, and

adults. During the spring in

Pennsylvania, groups of cowbirds

were observed moving through the

forest canopy and consuming large

numbers of gypsy moth larvae. The

brown-headed cowbird is an

opportunistic feeder and takes

advantage of any readily available

food source, such as the gypsy

moth, when it becomes abundant in

the environment.

30
Mammals

Mammals, which live in all types of

habitats, have perhaps greater

predatory impact on sparse gypsy

moth populations than any other

group of predators. Because of the

numbers, distribution, diets, and

agility of mammals, most forest

insects probably become available

prey to them during some stage of

an insect's life. The impact of

mammals is essential if the gypsy

moth predator community is to have

a regulatory effect.

Mammalian predators of the gypsy

moth that have been studied include

rodents, insectivores, carnivores,

and marsupials. Unlike birds, these

predators are not very conspicuous

nor easily watched because most of

them are active only at night. They

are less transitory than birds and

are more stable residents within an

area. They usually have greater

population densities than birds,

commonly reaching levels four to

eight times higher than songbirds

occupying the same area. Small

mammals often reach densities of 37

to 100 adults per hectare during the

spring and increase to much higher

levels later in the year.

Although mammals have the

greatest impact on insects that

spend part of their development on

the ground, they are certainly not

restricted to ground level. Squirrels

and chipmunks, which eat many

insects during certain seasons, are

not the only mammals that forage in

trees. White-footed mice commonly

climb trees to find food, often

nesting in abandoned woodpecker

holes or bird nests.

In an attempt to gain a better

understanding of the predator

potential of mammals, 15 common

woodland mammal species were

observed in the wild and in

captivity. Study objectives were to

identify the major mammalian

predators of the gypsy moth, the life

stages of the insect that are eaten by

each predator, the quantities eaten,

and ways to increase the most

important predators' effectiveness

through management.

Caged mammals were given gypsy

moth larvae, pupae, and adults with

and without alternative foods.

Observations in the laboratory gave

no indication that any mammal

tested would eat gypsy moth eggs.

This was true even when the

mammals were given no alternative

foods. In several instances,

individual mammals would knock

the egg masses apart but were never

observed eating them. To verify the

observations made on these caged

31
mammals, stomachs were examined

from snap-trapped small mammals

and road-killed raccoons, skunks,

and opossums, all collected from

within an area of moderate gypsy

moth density. Gypsy moth remains

were found in the stomachs of all 15

species, revealing that in the wild

the gypsy moth is available food and

is eaten by all these species.

After completing analysis of habitats

and densities of the mammals and

their feeding behavior, it was

determined that white-footed mice

and shrews have significantly

greater predator potential than other

species.

White-footed mice have

demonstrated their ability to eat

large numbers of gypsy moths in the

wild. After an intensive study of this

species and the many other gypsy

moth predators, the white-footed

mouse is recognized as the single

most important predator of the

gypsy moth.

A small mammal food preference

study (conducted in the wild with

healthy gypsy moth pupae placed in

the litter) indicated that shrews

(both shorttail and Sorex sp.)

accounted for approximately onehalf of the gypsy moth mortality

attributed to small mammals.

Remains of gypsy moth larvae and

pupae have been found in both

stomachs and droppings of shorttaiil

shrews collected within a sparse

gypsy moth population.

Rodents

White-Footed Mouse {Peromyscus leucopus)

The white-footed mouse (fig. 14) has

received more attention than any

other predator of the gypsy moth.

Recent studies have emphasized the

beneficial impact of this animal in

sparse gypsy moth populations

(CampbeU and Sloan 1976, 1977),

their feeding behavior, and even the

feasibility of managing this species

(Smith 1975) to increase its

effectiveness against the gypsy

moth.

The white-footed mouse (average

weight about 20 g) is the most

common and most widely

distributed small mammal in the

Northeast. It lives in all habitat

types, from suburban lawn edges to

mature forests, but is most abundant

in thick brushy areas. Under ideal

conditions, spring breeding densities

can reach 13 mice per hectare, with

densities later in the year reaching

two to three times that number.

Each breeding season, adult female

mice produce an average of three

litters of approximately four young

per litter.

White-footed mice have remarkable

agility and thoroughly explore and

utilize their habitat, nesting and

foraging from below the ground to

tree tops. Their diet consists of a

variety of seeds, nuts, and insects,

and their feeding behavior is truly

opportunistic. Insects form a

substantial part of this mouse's diet,

so it is not surprising that the whitefooted mouse preys on the exotic

gypsy moth when it is available.

The mouse has an interesting way of

eating the hairy gypsy moth larvae.

32
It grasps the insect with its forepaws

and pulls back the head capsule

with its teeth, discarding it along

with the bright-green upper digestive

tract. While rolling the insect's skin

back, just as a sock might be rolled,

the mouse eats the body fluids and

some internal membranes. In the

woods, larval remains (fig. 15) are

most likely to be found at the base

of host trees but have been found 30

feet up in trees.

The process of rolling back the

larval skin is learned by the mouse

to avoid irritation from the gypsy

moth larvae's protective hairs.

Young mice usually have an

unsuccessful first encounter with

larvae. A mouse will sniff a larvae,

as it does other foods, but if it gets

too close, the larval hairs become

embedded in the mouse's nose. The

mouse's second approach is more

cautious, and soon the larvae is a

regular part of its diet.

White-footed mice usually eat pupae

by opening one end and eating the

contents, but many times they will

simply tear apart pupae and eat

them. The mice will select female

pupae over the smaller males, but

both are eaten. Mice do not store

Figure 14.—White-footed mice

eating larvae.

33
pupae, as they do some other foods.

Gypsy moth adults (male and

female) are also eaten by the whitefooted mouse. After capturing a

moth, the mouse eats the entire

body, normally leaving the wings

and legs (fig. 16). It is interesting to

note that these mice, which

apparently do not eat gypsy moth

eggs, do eat the abdomen of the

adult female, including the eggs

within.

The number of insects eaten by an

animal in captivity does not

necessarily indicate how many that

animal will eat in the wild, but it can

provide a rough idea of the

maximum number that could be

destroyed over a certain time

period, hi captivity, white-footed

mice with alternative foods (apples

and mouse chow) have eaten as

many as 46 of 50 fifth-instar larvae

over 24 hours. Mice without

alternative food have eaten 50 of 50

fifth-instar larvae. Mice have eaten

as many as 20 of 40 pupae with an

alternative food, and 28 of 40 when

no alternative food was provided.

Overall, mice ate an average of 90

percent of the larvae offered when

no alternative food was given and

about 60 percent with an alternative

food. Alternative foods had no

effect on the number of pupae

eaten; in both cases mice ate an

average of 30 percent of the pupae

offered.

15

Figure 15.—Larval remains left by

white-footed mouse.

Figure 16.—Adult female remains

left by white-footed mouse.

34
Jumping Mice (Woodland, Napaeozapus

insignis, and Meadow, Zapus hudsonius)

^4

Jumping mice (fig. 17) are about the

same size as white-footed mice

(about 20 g) but are easily

distinguished from white-footed

mice by their long tail and large hind

feet. The meadow jumping mouse is

normally found in damp, long-grass

meadows; the woodland jumping

mouse is found in mature or

maturing forests, usually along

streams or pond edges. These

mammals never reach high spring

breeding population densities even

in ideal habitats but average three to

five per hectare. The jumping mice

demonstrated a low predatory

potential by eating a few larvae and

some pupae. Gypsy moth remains

left by jumping mice look similar to

those left by white-footed mice.

Figure 17.-

mouse.

-Meadow jumping

35
Chipmunks and Squirrels

Boreal Redback Vole (Clethrionotnys

Redback voles (fig. 18) are slightly

larger than mice (about 25 g) and

may reach fairly high spring

population densities (six or more per

hectare) in some areas of the

Northeast. Redback voles are

normally found in thick hardwood

forests and moist coniferous forests

with decaying logs and stumps.

They seem to prefer damp forest

situations but are also commonly

found in drier areas, if thick cover is

available. Redback voles, as are

shrews, are active day and night.

Like other voles, they feed mainly

on vegetation but also eat a variety

of insects. In the laboratory redback

voles demonstrated little predator

potential toward gypsy moth larvae,

but often ate pupae. On several

occasions they were observed

carrying pupae back to their nests in

their mouths.

Figure 18.—Boreal redback vole.

Although the bushy-tailed rodents

(chipmunks and squirrels) are often

considered seed eaters, they do eat

a wide variety of foods and are

seasonally insectivorous (Burt

1957). They use insects in their diets

in the spring and early summer

when preferred foods such as stored

nuts and acorns are scarce.

The bushy-tailed rodents

(chipmunks, gray squirrels, red

squirrels, and southern flying

squirrels) did not adjust well to

captivity, and their feeding behavior

was difficult to observe. In captivity

all these rodents preferred pupae

and larvae. None of the rodents ate

many larvae (5 to 10 percent of

those offered), and larval remains

were often crushed and only partly

eaten, or killed but not eaten.

Although gray squirrels were

observed removing gypsy moth

larvae from bark flaps in the forest

(Campbell 1975), and chipmunks

have been observed climbing trees

to capture adult moths (ODell 1977),

any impact they might have on

gypsy moth populations would most

likely come from pupae prédation.

When eating pupae, these rodents

grasp the pupal case with their

forepaws and eat it much as they

would an acorn. They usually eat

the entire pupa, but occasionally

large, scattered fragments of the

pupal case remain.

36
Chipmunk (Tatnias striatus)

The eastern chipmunk (fig. 19),

which weighs approximately 75 g,

often reaches spring populations of

eight per hectare and is found in

forests, in most thick, brushy

habitats, and along forest edges and

lawns. Although the chipmunk is

active during the day, it is most

active at dawn and dusk. The

chipmunk normally has two litters

of four young per litter per year.

Figure 19.—Chipmunk eating

pupa.

37
Gray Squirrel tßciurus carolinensis) Red Squirrel (Tamiasciurus hudsonicus)

The gray squirrel (fig. 20), weighing

approximately 500 g, is basically

arboreal (found in trees) but does

spend some time foraging on the

ground. The gray squirrel is found in

hardwood forests and forest edges,

around suburban and urban

environments, or wherever there are

ample food and nesting holes. Gray

squirrels normally have two litters

of four young per litter per year.

Spring breeding population densities

in good habitats often reach 12 per

hectare. Like the chipmunk, the

gray squirrel is most active at dawn

and dusk.

Red squirrels, which weigh

approximately 180 g, are usually

found in pine, spruce, or mixed

forests. Although they reach their

highest spring densities (two per

hectare) in the preferred conifer

forests, they are also found in

northeastern hardwood forests. The

red squirrel normally has two litters

of four young per litter per year. The

red squirrel is active throughout the

day, from early morning to late

evening.

Figure 20.—Gray squirrel.

38
Southern Flying Squirrel {Glaucomys

volans)

The southern flying squirrel,

approximately 65 g in size, is

nocturnal and is found where nest

holes are available in maturing

hardwood forests and along forest

edges. This flying squirrel normally

has two litters of four young per

litter per year. It often reaches

spring breeding densities of two to

three per hectare.

Insectivores

Shorttail Shrew (Blarina brevicauda)

The shorttail shrew (fig. 21) is the

largest North American shrew

(average weight about 18 g) and is

the most populous insectivore in

many areas. These shrews are

common in a variety of habitats

(forests, grasslands, marshes, and

brushy areas) east of the Rocky

Mountains. Although abundant (two

to three litters of five to eight young

per litter per year, with populations

reaching 20 per hectare), shorttail

shrews are among the least

conspicuous of the forest mammals.

These shrews are seldom seen but

often heard rustling through the

litter as they search for food

beneath logs, stumps, rocks, and

leaf litter, and even in the surface

runways of rodents—all places

where gypsy moth larvae rest and

pupate. In addition to worms, snails,

and other small animals, nearly half

the shorttail shrew's diet consists of

insects.

Figure 21.

larva.

-Shorttail shrew eating

39
Masked Shrew (Sorex cinereus)

Shrews must spend most of their

time in search of food, as their

extremely high metaboHc rate

requires that they eat approximately

the equivalent of their own weight

each day. To meet their food

demands, shrews are active day and

night and rest only periodically.

A shorttail shrew eats a gypsy moth

larva by grasping the larva with its

forepaws, holding the insect against

the ground, rolling it over, and biting

it near the middle segment on the

ventral side. The bite injects a

poison secreted from glands in its

mouth that helps to subdue the

larva. The shrew then eats the head.

Seldom will the head capsule

remain; this is one way to

distinguish larvae eaten by shrews

from those eaten by mice. The

shrew then eats the larva, including

the gut from the ventral side. All

that remains is the skin from the

back, where the hairs are attached.

Caged shorttail shrews consistently

ate at least 65 percent of the larvae

offered and nearly all the pupae,

even when an alternative food

(canned dog food) was available.

Shrews eat large numbers of pupae;

unlike mice, they have not shown a

preference for the larger female

pupae over the smaller male pupae.

A shrew will usually pick up a pupa

and carry it below ground to a nest.

One adult shorttailed shrew was

seen making 15 separate trips to its

nest, carrying one pupa each time in

its mouth.

The masked shrew (fig. 22) is one of

the smallest mammals in the

Northeast, weighing only 3 to 4 g at

maturity. Like the shorttail shrews,

they are active day and night and

spend most of their time foraging in

the litter. Females may produce two

or three litters of up to seven young

per litter per year, and in optimum

habitats (maturing hardwood

forests) masked shrews may reach

spring densities of 20 per hectare.

Masked shrews readily eat larvae

and pupae, although they appear to

prefer pupae. Capturing a sixthinstar larva that may weigh half as

much as the mammal itself is no

problem for these shrews. The

manner in which they attack and eat

gypsy moth larvae and pupae is

similar to that of shorttailed shrews.

Masked shrews are certainly

capable of causing high mortality to

both gypsy moth larvae and pupae

located in the litter.

Figure 22.—Masked shrew eating

pupa.

40
Smoky Shrew (Sorexfumeus) Starnose Mole (fondylura cristata)

The smoky shrew (fig. 23) is one of

the largest (6 to 11 g) of the

longtailed shrews and may reach

spring population densities of eight

per hectare. The smoky shrew

normally has two litters a year of

five young per litter. The smoky

shrew has feeding habits similar to

other shrews and is active day and

night. These shrews prefer, and are

most abundant in, mature

northeastern forests where there is

a deep layer of leaf mold and litter.

Caged smoky shrews consumed

large quantities of both larvae and

pupae; when eating larvae they did

not appear to be disturbed by larval

hairs. Although the feeding behavior

of this shrew is similar to that of the

shorttailed shrew and the masked

shrew, the smoky shrew is less

likely to have as great an impact on

gypsy moth populations because its

densities are lower.

The starnose mole, a relatively large

insectivore weighing about 60 g, is

easily distinguished from other

moles by the fleshy projections, or

tentacles, on the end of its nose (fig.

24). This mole commonly inhabits

eastern hardwood forests but

reaches its greatest densities in

moist, swampy areas. Females

produce one litter of three to seven

young per year. These moles often

appear above ground, but unlike the

eastern mole they spend a

considerable amount of time

foraging in the litter. They are active

day and night, spending most of

their time, like the shrews, trying to

satisfy a voracious appetite.

Figure 23.—Smoky shrew eating

pupa.

Figure 24.—Starnose mole.

41
Carnivores

Striped Skunk (Mephitis mephitis)

Starnose moles seem to detect food

with the sensitive tentacles on their

nose, but their sense of smell

appears to be poor. This mole eats a

variety of foods, but insects

comprise about one-third of its diet.

Starnose moles are not considered

as important gypsy moth predators

as other insectivores. Although

caged starnose moles often ate

pupae, few larvae were eaten; the

stiff protective hairs on the larvae

seemed to irritate their tentacles. If,

however, larvae are found in the

tunnel of the starnose mole, they are

attacked and killed by this mammal,

which rigorously defends its tunnel

against all intruders.

The striped skunk (fig. 25) is one of

the best known mammals in the

Northeast. Skunks are found in a

variety of habitats, including

suburban yards, but prefer semiopen country with a mixture of

woods and brushland. Skunks have

one litter of as many as seven young

per yean Spring densities can reach

one per 2.4 ha, but more commonly

the densities range between 5 and 10

per 2.6 km^. Skunks have a varied

diet but rely heavily on insects as a

food source. It has been estimated

that insects comprise approximately

one-half their intake. Skunks are

chiefly nocturnal, emerging shortly

after dusk to begin their search for

food.

When a skunk eats a gypsy moth

larva, it beats the larva with its

forepaws, rolling the larva toward

itself as the skunk backs away.

Figure 25.—Striped skunk eating larva.

42
Raccoon (Procyon lotor)

When the protective hairs have

been broken and the larva has been

turned into a pulpy mass, the skunk

eats it. Skunks also eat gypsy moth

pupae and adults with ease.

In experiments with caged

mammals, skunks demonstrated the

greatest willingness of all the midsize mammals to eat gypsy moth

larvae and ate large quantities of

them. Individual skunks would

consistently eat 25 fifth-instar larvae

in 2-3 minutes. In one cage

containing five young skunks the

animals would actually try to take

larvae away from each other

The raccoon (fig. 26), which can

weigh 12 kg, is the largest mammal

that has been observed eating gypsy

moths. They are common along

streams and around pond and lake

borders if wooded or forested areas

are nearby, and in suburban and

urban areas where they are often

seen at night alongside highways or

raiding garbage cans. Raccoons have

one litter of approximately four

young per year and may reach

spring densities of approximately

three per square kilometer.

Figure 26.—Raccoon eating larva.

43
Marsupials

Although the omnivorous raccoon's

natural diet is most often thought to

be crayfish, frogs, fruits, nuts, and

bird eggs, it also eats large

quantities of insects. During the

feeding studies, caged raccoons ate

more than 90 percent of the larvae

and pupae given them. When it ate a

larva, a raccoon picked it up in its

forepaws and rolled it, or roUed it on

the ground or against some object,

to break it apart to make it more

palatable. The entire larva was then

eaten. Raccoons in the wild have

been observed picking the flightless

gypsy moth females from the base

of trees and eating them. All life

stages of the gypsy moth, except

deposited egg masses, have been

identified in the stomachs of wild

raccoons.

Opossum (Didelphis marsupialis)

The opossum (fig. 27) is the only

naturally occurring marsupial in the

United States. Adult opossums can

weigh as much as 6.5 kg and may

produce one or two litters of

approximately 10 young per litter

per year. Opossums prefer farm

areas but are also found in forests

and wooded areas, especially near

water. Opossums eat a variety of

food that includes fruits, vegetables,

meat, eggs, and insects. They are

opportunistic scavengers and reach

their greatest densities around

human habitation, where they can

forage in garbage. When opossums

are away from garbage sources,

insects form a substantial portion of

their diet, so it is not surprising that

the gypsy moth is part of this

mammal's diet. The opossum is the

only mammalian predator of the

gypsy moth that appears unaffected

by the larval hairs. It simply grasps

a larva and eats it whole.

Opossums in captivity ate

approximately 80 percent of the

larvae offered, missing only those

that had crawled out of reach.

Movement by a larva increased its

probability of being eaten. When

attacking a gypsy moth larva, an

opossum would hold its head

motionless and then quickly strike

and grasp the larva in its mouth,

chewing and swallowing it in

seconds. Pupae were eaten in the

same way, but being immobile they

did not stimulate attack and were

eaten only when encountered.

44
Figure 27.—Opossum eating larva.

45
Amphibians, Reptiles, and Fish

Amphibians

When the role of vertebrate

predators of the gypsy moth is

discussed, the emphasis has been on

birds and mammals. However,

many species of amphibians,

reptiles, and fish have been

observed eating gypsy moth larvae

and adults.

Little is known about this group's

role as predators of the gypsy moth

or other forest insects. Because

these other vertebrates are

coldblooded, and their temperature

fluctuates to match the temperature

around them, their metabolic rate is

normally much lower than that of

birds and mammals. This lower

metabolic rate requires less food

and thus these coldblooded

vertebrates' potential for consuming

prey is low. It is doubtful, therefore,

that these vertebrate predators have

any significant impact on gypsy

moth populations. Nevertheless

they do eat gypsy moths and are

part of the gypsy moth predator

system.

Movement of prey appears to be the

key to food selection by the

amphibians, reptiles, and fish that

have been observed. This selection

is largely a random process, with

foods taken in proportion to

abundance and availability.

Unfortunately, when any pest insect

becomes abundant enough to

represent the major portion of the

diet of this group, it is unlikely that

predator pressure from even the

entire predator community,

including birds and mammals, has

an impact on the pest population,

because there are just too many

insects.

American Toad ißufo americanus)

The American toad (fig. 28) is

perhaps the most common and most

useful amphibian predator of the

gypsy moth. The American toad

was noted as a predator of the

gypsy moth as early as 18% by

Forbush and Fernald, when they

reported that these toads ate great

numbers of gypsy moth caterpillars

in infested brushlands. They

examined the stomachs of three

toads taken in that area and found

them to contain 7, 15, and 65 gypsy

moth caterpillars, respectively.

The American toad eats insects,

slugs, earthworms, and almost any

small invertebrate that moves. It is

found in a wide range of habitats

that have shallow water (for

breeding), moist hiding places, and

an abundant supply of insects and

other invertebrates (for food).

Observations of captive toads

suggest that when a toad is ready to

eat and it encounters a gypsy moth

larva, the larva will be eaten. Toads

actually stalk larvae that are

crawling on the litter and then

quickly seize them with their sticky

tongues.

46
Fowler's Toad (Bufo woodhouseifowleri)

The Fowler's toad (fig. 29), named

after a Massachusetts naturalist, is a

common toad of the Atlantic coastal

plain; inland distribution is spotty. It

is often confused with the American

toad. The two species can usually

be distinguished from one another

by the number of warts in each of

the dark spots on their backs—

Fowler's toad has three or more; the

American toad has one or two.

Fowler's toads have been observed

eating gypsy moth larvae (fourth

and fifth instar). Their method of

stalking and seizing of the insect is

similar to that of the American toad.

Figure 28.—American toad eating

larva.

Figure 29.—Fowler's toad eating

larva.

47
Wood Frog {Rana sylvatica) Gray Tree Frog (Hyla versicolor and Hyla

chrysoscelis)

Wood frogs (fig. 30), which range

farther north than any other North

American amphibian or reptile, can

be found in most moist wooded

areas throughout the current gypsy

moth infested area. Wood frogs,

easily recognized by the black patch

behind the eye, are often found

considerable distances from water.

Forbush and Fernald (1896)

reported wood frogs attacking adult

female gypsy moths. Recent

observations have confirmed that

they also attack gypsy moth larvae.

Figure 30.—Wood frog.

Figure 31.—Gray tree frog.

These two species are so similar in

appearance they have long

masqueraded as one and can only

be distinguished from one another in

the field by their voices. Figure 31

shows Hyla chrysoscelis. Forbush

and Fernald (18%) reported tree

frogs eating gypsy moth caterpillars.

Although they usually forage for

food in trees and shrubs near or

even in water, tree frogs have been

observed in trees at least 2(X) m

from any open water. Although gray

tree frogs have not been observed

eating gypsy moths, it is probable

that the moths are eaten when

encountered.

48
Reptiles

Green Snakes (Genus Opheodrys) Other Snakes

Two species of green snakes occur

within the gypsy moth's range, the

terrestrial smooth green snake and

the more arboreal rough green

snake. Although sometimes

common, both species are difificult

to see because they are so well

camouflaged. Although green

snakes have not been observed

eating gypsy moths, it is known that

larvae of moths and butterflies form

a substantial portion of their diet

(Palmer and Fowler 1975). The

rough green snake is an excellent

climber and often forages for insects

in small trees and shrubs.

Garter snakes (Genus Thamnophis)

and eastern hognose snakes

{Heterodon platyrhinos) (fig. 32)

may occasionally eat gypsy moth

larvae. The diet of young hognose

snakes consists mainly of insects;

the adult hognose snake eats toads

and a variety of other foods but few

insects.

Figure 32.-

snake.

-Eastern hognose

49
Northern Fence Lizard (ßceloporus undulaíus)

331

^'Wmwî

m.r

- - --IE«

^

1' ^

,'^^^^t'''

.SsT V^ '

' 1

The northern fence lizard (fig. 33) is

a small, spiny reptile that ranges

north into Pennsylvania and New

Jersey. Fence lizards are excellent

climbers and are often seen in trees

as well as on rotten stumps and

logs. Fence lizards feed almost

exclusively on insects. They have

been observed eating gypsy moth

larvae and adult males in captivity,

and because of this and because

fence lizards spend a considerable

amount of time where gypsy moth

larvae rest, it is assumed that the

gypsy moth is part of this lizard's

diet. A fence lizard is attracted by

the movement of larvae. It will

lunge at the insect with its mouth

open, clamp itsjaws around the

insect, and in successive gulps

swallow a larva whole and alive.

Figure 33.—Northern fence lizard.

50
Fish

Invertebrate Predators

It is interesting that forest pest

insects are found even in the

stomachs offish. Local fishermen

have reported finding gypsy moth

larvae in the stomachs of brown and

rainbow trout. Although gypsy moth

larvae and adults are occasionally

eaten by a variety offish species,

including trout, bass, bluegills, and

sunfish, it is very doubtful that any

real economic importance can be

attributed to this prédation. Gypsy

moth larvae and adult moths often

fall or are blown into lakes, ponds,

and streams, becoming available

food for fish.

Most people who fly-cast realize

that the wooly-worm fishing lure is

simply an imitation of a hairy

caterpillar. Brook trout have been

caught in mountain streams in

Pennsylvania on both live gypsy

moth larvae and adult moths, and

bass and bluegills have been

observed taking larvae from the

water surface at the edge of a small

lake.

In comparison to vertebrate

predators (birds and mammals),

little is known about invertebrate

predators of the gypsy moth. Exotic

invertebrate predators have been

imported, studied, and in some

cases released, but very little is

known about their impact on gypsy

moth populations. Studying the

impact and selective feeding

behavior of small mammals brought

to light that certain native

invertebrates, namely ants and

harvestmen, had considerable

predator potential. Their potential

had been overlooked because of the

emphasis on small mammals.

Emphasis should be on the

vertebrates. Ignoring invertebrates,

however, would lead to some loss of

appreciation and understanding of

the importance of vertebrate

predators. It is therefore essential to

examine all the components of

prédation in order to assess the

value of any predator or group of

predators within a system.

Invertebrate predators are much

more important than was generally

thought. Campbell and Sloan (1976),

when assessing gypsy moth

mortality factors, assumed that

missing pupae had been carried

away or eaten by vertebrates.

However, recent field observations

indicated that many of the missing

pupae classified as killed by

vertebrates could actually have been

killed and removed by

invertebrates.

51
In a field experiment, ants and

harvestmen removed a substantial

portion of the pupae (both

parasitized and healthy) that were

artificially placed under small

wooden shelters in the litter or that

were allowed to spin up and pupate

in those shelters. Pupae attacked by

invertebrates had finely serrated

edges that easily distinguished them

from those attacked by small

mammals. A peppering effect

caused by pupal case remains left

on the boards also indicated

invertebrate activity; on litter this

peppering would have gone

unnoticed. Whether the

invertebrates are acting as

scavengers or predators is still being

studied.

The impact invertebrate predators

can have has been demonstrated on

several agricultural crop pests

within simple systems

(monocultures), but within the

complex forest ecosystem it is

difficult to measure invertebrate

predatory impact on gypsy moths.

Furthermore, two problems arise

when trying to include invertebrate

predators in an integrated pest

management system: Invertebrates

are not abundant in all areas, and

they are often dependent on the

density of their prey. Even within

these limits, however, they can have

a significant impact, as in the case

reported by Campbell (1975), when

Calosoma beetles caused heavy

mortality to a gypsy moth

population. Again, invertebrates are

part of the predatory system and

cannot be discounted, even if their

prédation appears negligible, if an

integrated pest management

program is to be successful.

To understand the impact of

invertebrate predators, it is

necessary to consider the total

number of species, the density

potential, and the diversity of

habitats. It is then easy to see that

as a group they could have

significant economic potential, not

only as predators of the gypsy moth

but also as predators of other forest

pest insects. Many entomologists

would agree that most of the

invertebrate predators of the gypsy

moth have not yet been identified.

This section discusses those that

have received the most attention

and those that are most familiar.

52
Ground Beetles (Carabidae)

This very large family of

approximately 2,500 species in

North America is believed to be

generally beneficial because of the

predaceous habits of both larvae

and adults. Several species have

been reported as predators of the

gypsy moth; one species, Calosoma

sycophanta (fig. 34), has been

imported from central Europe and

released in New England to help

control the gypsy moth. The genus

Calosoma has the reputation as

being a fierce caterpillar hunter; this

is reflected in the common names of

some of the native species—^fiery

hunter {Calosoma calidum) and

fiery searcher {Calosoma

scrutator).

Ground beetles hide during the day

under stones or logs or under the

surface of the soil and hunt chiefly

at night. The adult beetles ofC

sycophanta, C.frigidum (fig. 35),

and C. scrutator actively pursue

their prey in trees; the larvae of

these species forage in the litter.

Larvae of the imported C.

sycophanta are good climbers and

are often seen on trees eating gypsy

moth larvae and pupae.

C. sycophanta is the principal beetle

that attacks gypsy moth. Although

abundant only in certain locales, it is

now well estabUshed in infested

areas. It is usually observed,

however, only when there is an

abundance of gypsy moths. These

beetles were first imported in 1905

and released in 1906. None have

been released since 1926.

C. sycophanta is large (sometimes

exceeding 3 cm) and can easily be

recognized by its brilliant iridescent

green wing covers. (Native species

are predominantly black.) The adult

beetle's life cycle is synchronized

with that of the gypsy moth; adults

Figure 34.—Ground beetle

(Calosoma sycophanta).

53
emerge in early June when gypsy

moth caterpillars are available and

go into hibernation soon after egg

laying is started. Beetle larvae

appear from the end ofJune to the

middle of July.

The predatory potential of ground

beetles has been demonstrated in

feeding experiments conducted by

Burgess (1929). He noted that a

single larva of this predator will

destroy at least 50 full-grown gypsy

moth larvae during its 2 weeks of

development and that the adult

beetle, which lives from 2 to 4 years,

will destroy several hundred larvae.

Ground beetles of other genera—

Cambus sp.,Agonum sp., and

Harpalus sp.—have also been

observed eating gypsy moths.

Despite this high attack potential,

which was demonstrated with an ad

libitum gypsy moth diet, it remains

questionable what impact these

beetles have within low-density

gypsy moth populations. However,

this beetle's predator potential is

increased because it is long lived (2-

4 years), can suffer hunger for a long

time, and is unaffected by

unfavorable climate conditions.

Figure 35.—Ground beetie

(Calosoma frigidum).

54
stink Bugs (Pentatomidae)

Although most members of this

family are plant feeders, some

predators do exist. Both nymphs

(fig. 36) and adults of the native

spined soldier bug {Podisus

maculiventris) have been observed

killing gypsy moth larvae and pupae.

This insect is said to be "the most

useful of the American predaceous

Hemiptera" (Swan and Papp 1972).

Figure 36.—Pentatomid nymph

eating pupa.

55
An exotic pentatomid,

Dinorhynchus dybowskyi (fig. 37), a

predator of gypsy moth larvae,

pupae, and adults in Japan, has been

imported to study the feasibility of

establishing it in this country. The

insect is currently in quarantine.

Figure 37.—Ifentatomid adult

eating arctiid larva.

56
Ants (Formicidae)

Ants have long been recognized as

important predators of some insects.

In many countries, ant hills are

protected by law and have also been

moved and fenced in (for their own

protection) to help control pest

insects.

In this country ants have been

observed eating or tearing apart and

removing gypsy moth eggs, larvae,

pupae, and adults. Black carpenter

ant workers {Camponotus

Pennsylvanieus, fig. 38) have been

observed attacking adult female

gypsy moths in the process of

depositing egg masses. These adult

moths were torn apart and carried

away. Both black and red carpenter

ant workers {C. ferrugineus) attack

healthy male and female gypsy moth

pupae.

Along with chickadees, ants have

been the only observed predators of

gypsy moth eggs. Campbell (1975)

reported that ants, by removing one

egg at a time, were successful in

destroying several egg masses

within a sparse gypsy moth

population.

The significance of ant prédation on

sparse gypsy moth populations may

be greater than previously realized,

and the impact of ant prédation on

gypsy moth pupae located in the

litter is currently being studied.

Figure 38.—Black carpenter ant

eating pupa.

57
Harvestmen (Phalangüdae)

Often called daddy longlegs (fig. 39),

these invertebrates are familiar to

all. Although these invertebrates are

arachnids and look like spiders, they

belong to the order Phalangida.

Harvestmen have been thought of

as scavengers of little economic

importance. Actually, little is known

about their food habits, and

scientists disagree about what foods

are selected. A few hours spent

observing them will demonstrate

their ability to capture and kill a

wide variety of insects and other

invertebrates. In a Connecticut area

study, two common northeastern

species of harvestmen, Leiobunum

longipes andL. politum, were seen

feeding daily on both healthy and

parasitized gypsy moth pupae. On

several occasions two or three

harvestmen attacked and fed on the

same gypsy moth pupa. Because

harvestmen feed on both healthy

and parasitized pupae, it is difficult

to determine whether they act more

as scavengers or as predators.

Harvestmen live in a variety of

places; some species are active

during the day and others are active

at night. In the Connecticut study

after a warm summer rain one

evening, harvestmen appeared to be

everywhere. That night 30 trees of

varying sizes and species were

examined at random for 60 seconds

with flashlights. On each tree, from

the ground to 2.4 m up, was at least

one harvestman, and some trees

had as many as 12. Because

harvestmen are so abundant, utilize

a wide variety of foods, and forage

on trees and in the litter, it is

probable that even in sparse gypsy

moth populations they will remove

some pupae. It would certainly be

wise to investigate further their

predator and impact potential.

Figure 39.-

pupa.

-Harvestmen eating

58
Spiders (Araneida)

Spiders live everywhere and eat

almost any living invertebrate

provided it can be overpowered.

Spiders are known to be beneficial

because they destroy a large

number of insects, but they are

rarely mentioned as predators of

forest pest insects. Forbush and

Fernald (1896) listed 11 species of

spiders from six families that they

had seen attacking gypsy moth eggs,

larvae, pupae, or adults.

Figure 40.—Wolf spider.

During the summer, spiders become

abundant throughout woodlots and

forests, inhabiting the ground as well

as plants of all kinds, from grasses

to trees. Spiders are divided into

two groups, on the basis of the way

they capture their prey: Hunting

spiders, which run on the ground or

59
on plants, catching insects wherever

they find them, and cobweb spiders,

which capture their prey in webs.

Lycosids (fig. 40) are hunting

spiders known to eat gypsy moth

larvae. They are keen-sighted, swift,

long-legged running spiders.

Lycosids are often called wolf

spiders because they run down their

prey. Attids, orjumping spiders (fig.

41), are also a type of hunting spider

known to eat gypsy moth larvae.

They are usually short and stout,

often brightly colored, and quick in

their movements. Forbush and

Fernald (18%) wrote about

Phidippus tripunctatus, a jumping

spider: ". . .it was brought into the

insectary and supplied with gypsy

moth caterpillars, which it readily

destroyed." This species is very

common, and because it Uves under

sticks and stones it is certain to

encounter gypsy moth larvae that

search for daytime resting locations

in the litter.

Figure 41.—Jumping spider.

60
Figure 42.—Theridid spider

with larva caught in web.

Spiders that construct cobwebs are

often successful in trapping gypsy

moth larvae and occasionally adults.

The theridid spider in figure 42 has

captured a gypsy moth larva in its

web. Theridids build loose and

irregular-shaped webs between

leaves and branches of low trees

and bushes.

Spiders could have some potential

impact on sparse gypsy moth

populations. Unfortunately,

necessary priorities toward the

more important gypsy moth

predators have prevented study of

these interesting animals.

61
Other Invertebrate Predators

There are other invertebrates

known to eat gypsy moths: The

spined assassin bug, flower fly,

green lacewing, baldfaced hornet,

and European mantid (fig. 43) are a

few. Even mites are known to

destroy gypsy moth eggs. The point

is that each of these invertebrates,

in what often appears to be an

insignificant way, adds to the

collective importance of prédation

as an often-regulatory force.

Figure 43.—European mantid

eating larva

62
Reexamining Our Wildlife

Perceptions

The factors of predator potential,

predator impact, alternative foods,

prey and predator density, and food

availability remind us that we are

dealing with nature's normal,

effective, and continually operating

mechanisms, which are subject to

change at any time.

In the 1976 New Lisbon, N.J.,

example, the abundance of

cankerworms for all practical

purposes had negated the impact of

white-footed mice on the gypsy

moth. It has already been mentioned

that when small mammals are

experimentally removed from places

where gypsy moth populations are

sparse and stable, the moth

populations may increase by greater

than tenfold in just 1 year. However,

in the New Lisbon population,

although mouse density was very

low, no apparent increase in the

gypsy moth population occurred the

second year. Certainly the potential

for an increase was there, and users

of predator/prey systems in pest

management programs must think in

terms of what will happen to the

target (pest) insect if any one of the

many variables occurs.

Just as important as understanding

the effects of these variables are the

perceptions of wildlife that most

people develop throughout their

lives. The word ''predator" conjures

up images of large animals—^wolves,

coyotes, and mountain lions, or

eagles, hawks, and owls; small

animals such as mice, shrews,

warblers, robins, and even insects

are seldom thought of as predators.

A chipmunk is thought of with an

acorn in its mouth rather than an

insect pupa; a shrew, searching for

worms rather than for gypsy moth

caterpillars; or an ant, carrying away

picnic crumbs rather than gypsy

moth eggs.

These perceptions can be difficult to

change and often prevent us from

seeing what is really happening.

Campbell (1975) reported that

shrews seldom come in contact with

gypsy moths in the natural state. We

have now learned that shrews not

only come in contact with gypsy

moths but also that they often eat

them in significant amounts.

It is possible that our observations

of amphibians, reptiles, and even

fish as predators of the gypsy moth

may be just as incomplete. This

report, therefore, stresses that all

predators must be considered as

having an impact on gypsy moth

populations. It took half a century

from the time Forbush and Fernald

discussed bird prédation until

mammals were mentioned as an

important part of gypsy moth

population dynamics. Another 25

years passed before researchers

began to quantify the predatory

potential and impact of mammals on

sparse gypsy moth populations.

63
Conclusion

It should no longer be assumed that

other groups of animals are

insignificant as predators offorest

insects. Given certain circumstances

or conditions, they may be

important. They are all members of

the predator community, and within

that context they and their role in

gypsy moth population dynamics

have been discussed. It is the

collective impact from this complex

predator community that we should

try to understand and utilize in

future management programs. To

successfiilly accomplish this, we

must start by reexamining and

adjusting our wildlife perceptions.

A principal objective throughout the

gypsy moth research program has

been to develop an understanding of

the role and importance of prédation

in the population dynamics of the

gypsy moth. Over the last few years

a great deal has been learned about

the gypsy moth predator complex,

and several characteristics that

make predators a major suppressive

force well suited for a specialized

role in an integrated pest

management system have been

discussed. However, further

information is needed before we can

successftilly integrate our

knowledge of gypsy moth predator/

prey theory with biologicaUy and

economically feasible practice so

that forest managers can use

predators in an effective and

practical control program.

Particular emphasis in future studies

should be placed on understanding

the foods and feeding habits of the

predators so that they can be used

effectively in an integrated pest

management program. Also,

because predator impact is closely

associated with alternative foods,

we need a better understanding of

annual food production, variety,

quantity, and variability within

northeastern hardwood forests.

The predator/prey system discussed

in this booklet is complex, being

composed of many predator species

that eat a variety of foods. These

predators are all opportunistic and

select food largely as a function of

availability and abundance.

Although a preferred food may be

eaten in great quantity, these

64
predators attempt to vary their diets

and are always testing other

potential food sources; in this

process gypsy moths are eaten by

many predators. It is the collective

impact of all these predators that

leads to their importance in

maintaining certain sparse gypsy

moth populations.

If the gypsy moth predator system

were simple, with one or a few

predators dependent upon a

particular pest insect for food, the

impact and precise role of prédation

would be easier to predict and

determine. On the other hand, the

complexity of the gypsy moth

predator community may actually

give greater year-to-year stability

and be a major reason why some

gypsy moth populations remain

sparse and stable for several years.

Certain aspects of the role of gypsy

moth predators are fairly well

understood, while many others have

not yet been determined. This is

probably best exemplified by

research experience. The available

information in the early 1970's led to

the belief that when significant

prédation of gypsy moth pupae in

sparse populations occurred, it was

contingent upon white-footed mouse

activity. It was then hypothesized

that through management to

increase populations this important

predator might be made even more

effective. In one study, white-footed

mouse populations were managed

by providing supplemental food and

nest boxes from 1973-76, which

resulted in a significant annual

increase in mouse density. However,

the real significance of this study

was not realized until after a second

study. It seemed that the next logical

step was to measure the impact of

the increased mouse density on the

survival of gypsy moths. A study

was therefore designed to determine

the feeding behavior of white-footed

mice in relation to healthy and

parasitized male and female pupae

placed in the litter.

In retrospect it was probably overly

optimistic to believe that the precise

impact of the mice on the pupae

could be determined. By the end of

the field season it was not readily

apparent, without the aid of a

computer to assist in analysis,

whether mice, shrews, or even

invertebrates (ants and harvestmen)

had eaten more pupae. Mice may

well be the most important predator

of gypsy moths, but it was found

that they were getting a lot of help.

During that study came the

realization of how little was known

about the components and

interactions within the total gypsy

moth predator community. Perhaps

most surprising was the abundance

of activity of the invertebrates as

they scavenged the parasitized

pupae and attacked healthy pupae.

65
The high susceptibility of parasitized

pupae to attack by all of these

predators certainly warrants further

investigations. High parasite

mortality related either directly or

indirectly to vertebrate and

invertebrate predatory behavior

may be a significant factor

contributing to the ineffectiveness of

parasites in this country (Reardon

1976, CampbeU and Sloan 1977). An

appreciation of the complexity of

this predator/prey system comes

forth when it is remembered that

the study focused only on one life

stage (the pupa), in one location (the

litter) in one forest.

Buckner (1966), in discussing the

role of predators in the biological

control of forest insects, stated

''particular emphasis should be

placed on the factors governing the

abundance of the various predators

so that advantage may be gained

from the large groups of potentially

important predators whose

members are not related closely to

the abundance of the prey." Human

activity and land use practices often

govern the abundance and

distribution of a large number of

predators and can have tremendous

impact on species that are important

predators of forest pest insects. It

seems appropriate, therefore, to

make a few comments about the

concept of managing these predators

and their basic needs.

"The general needs of all animals

are much alike in that each must

have a sufficient quantity and

variety of food and protective cover

to meet its physiological needs for

maintenance, growth and

reproduction throughout its life"

(Trippensee 1948). In all habitats

there is a limitation on the number

of animals of each species that an

area can maintain or support; this is

referred to as the carrying capacity.

The population of each species

adjusts to the carrying capacity for

each area. Every time a significant

habitat change occurs in an area, the

animal populations, given proper

time, readjust to the new carrying

capacity. Depending on the actual

change that took place, wildlife

number and diversity can increase,

decrease, or remain the same.

Generally, however, if food and

cover are increased, wildlife

populations increase. (Each species

does have certain limits beyond

which their populations cannot

increase. These limits are often

referred to as tolerance density, a

point where intraspecific

competition and crowding take

place and become the population's

controlling mechanism.)

Forest managers wishing to employ

predator management for insect

control can either increase native

predator populations, release exotic

predator species, or do both. The

release of exotic predators is not

and should not be an attempt to

release a large number of predators

available for immediate control—

this will not work. Rather, it should

be an attempt to establish a breeding

population of a particular predator

where it previously did not exist.

66
The introduction of the masked

shrew from mainland Canada into

Newfoundland to control larch

sawfly is one example of a

successful attempt to establish a

breeding population of a vertebrate

predator to control a forest pest

insect.

Figure 44.—Forest "cleaned up.'

The idea of managing a particular

predator or predators to combat a

forest pest insect is not new.

Buckner (1966) described a

successful attempt by Hamilton and

Cook in the 1930's to protect a

plantation of larch in New York

State from an outbreak of the larch

sawfly. They supplied nest boxes

and brush piles that provided a

significant habitat change that

67
produced an abundance of deer

mice, redback voles, and masked

shrews. Each of these mammals has

a relatively high insectivorous diet,

and the increase in their numbers

led to a reduction in the number of

sawflies in the managed plantations.

In the unmanaged control areas,

sawflies remained at outbreak levels

for years.

Providing and/or improving food

and cover for wildlife can increase

the density of wildlife. Populations

of birds and mammals can often be

raised simply by increasing the food

supply. Feeding has the advantage of

being easily turned on and off; with

proper manipulation a manager

could change at will a species from

eating the feed back to a natural diet,

including insects. However, feeding

has the disadvantage of being

expensive, nonselective, and

effective for only a short term.

A more reasonable way to increase

population densities of useful

vertebrates is through silvicultural

habitat manipulation, encouraging

plant species that have the capacity

of supplying both food and cover.

To manage a species through habitat

manipulation, it is necessary to

understand the habitat requirements

for each species and whether those

requirements can be manipulated in

an economically and ecologically

feasible manner to achieve the

management objectives. In each

case, it must be determined if the

habitat can be manipulated in a way

to increase the abundance of the

vertebrates that eat gypsy moths.

Fortunately, many species of birds

and small mammals respond

favorably to relatively simple habitat

changes. Creating dense ground

cover, one of the most important

requirements offorest-dwelling

small mammals, can effectively

increase small-mammal populations.

Its importance for large populations

of small mammals cannot be

overemphasized.

Populations of hole-nesting birds

have been successfully increased by

providing them with nest boxes. In

parts of the Soviet Union, nest

boxes have been used to increase

bird numbers in an integrated

management system for a complex

of forest-defoliating insects,

including the gypsy moth.

What can forest managers and

homeowners do to help increase,

maintain, and create a more diverse

predator community? Homeowners,

unfortunately, often seem compelled

to clean up their property and turn

natural brushy areas into lawn (fig.

44), thereby removing the food and

cover needed by birds and

mammals. Foresters also are often

involved in similar large-scale

cleaning operations, which lead to

the elimination of the brush

competing with the trees. These

cleaning operations often drastically

reduce both vertebrate species

diversity and the total number of

birds and small mammals in the

area. The elimination of brush

68
removes the cover necessary for

bird species, which occur from the

ground to the lower canopy, and

eliminates much of the cover

necessary for small mammals.

Few people will manage their land

strictly for small mammals and

birds, but many foresters and

homeowners unknowingly turn

good wildlife habitat into unsuitable

habitat simply by removing the

brush. By understanding the

requirements of these predators,

one can actually manage for them

by not destroying their habitat, or at

least by trying to minimize the

impact of human activities on the

habitats of these animals.

It is hoped that the information

presented in this booklet has

increased the awareness of the value

and importance of prédation in

maintaining population stability of

forest insect pests. It is known that

prédation is a regulatory factor in

certain gypsy moth populations and

in populations of some other forest

pest insects. However, it must also

be realized that prédation is only

one of the forces suppressing insect

population growth in a forest

ecosystem. Although at times

predators may regulate gypsy moth

populations, they cannot regulate

them forever and they do not

regulate them alone.

Predators have in the past and will

continue in the future to be

important in the population

dynamics of the gypsy moth. Gypsy

moth populations in this country

usually appear to be at either

harmless or outbreak levels. One of

the keys to the harmless level is the

naturally occurring prédation by the

predator community. Since the best

way to cope with a problem is to

prevent it, it would be wise to use

predators in future attempts at

managing the gypsy moth.

As more is learned about prédation

and other processes within the

forest ecosystem, an appreciation

must grow of the importance of

slowly and patiently gathering the

facts from which conclusions are

drawn. Objectivity must be

maintained in order to put early

preconceptions in their proper

perspective and to gather

scientifically acceptable evidence

from which new research goals are

made and future pest management

programs are developed. The

success of future gypsy moth

management systems lies in our

ability to appreciate, understand,

and wisely use all the natural

suppressive mortality factors

operating within the forest

ecosystem.

69
Acknowledgments References

Special appreciation is given to

Roger Zerillo for the many hours

spent on the difficult and sometimes

frustrating job of photographing

most of the wildlife in this booklet.

We would like to thank the

following for their outstanding

contributions to this report. For

research assistance: Dan Arcieri,

Joel Bigelow, Paul Castelli, Nancy

DePalma, Paul Galipeau, Jean

Germe, Pat Goertz, Dan Holland,

Candy Hutchinson, Craig Scharf,

and Ron Sloan. For reviews and

comments of early drafts of this

report: Drs. Noble Proctor,

Southern Connecticut State College,

and Steve Berwick, Yale University.

For photographs: Harold Eno (fig.

14), Lt. Col. Murray Cragin, USAF

(figs. 40 and 41 ), Paul Schaefer (fig.

37), and Bob Neely (fig. 42).

We also thank the Encyclopaedia

Britannica Educational Corporation

for kindly allowing the use offigures

5-13, which were copyrighted 1%2-

64.

The quotes on page 11 are from

Ecology and Resource Management,

by Kenneth E. F Watt. Copyright

1968 by McGraw- Hill. Used with

permission of McGraw-Hill Book

Company.

Bess, H. A. 1%1. Population

ecology of the gypsy moth,

Porthetria dispar (L.)

(Lepidoptera:Lymantriidae). Conn.

Agrie. Exp. Stn. Bull. 646.

Bess, H. A., S. H. Spurr, and E. W.

Littlefield. 1947. Forest site

conditions and the gypsy moth.

Harvard For. Bull. 22.

Brown, W. L. 1%1. Mass insect

control programs: Four case

histories. Psyche 68:75-111.

Buckner, C. H. 1966. The role of

vertebrate predators in the

biological control of forest insects.

Ann. Rev. Entomol. 11:449-470.

Burgess, A. E 1929. Imported insect

enemies of the gypsy moth and the

brown-tail moth. U.S. Dep. Agrie,

Tech. BuU. 86.

Burt, W. H. 1957. Mammals of the

Great Lakes Region. Univ. Mich.

Press, Ann Arbor, Mich.

CampbeU, R. W. 1975. The gypsy

moth and its natural enemies. U.S.

Dep. Agrie, Agrie. Info. Bull. 381.

CampbeU, R. W., and R. J. Sloan.

1976. Influence of behavioral

evolution on gypsy moth pupal

survival in sparse populations.

Environ. Entomol. 5:1211-17.

CampbeU, R. W., and R. J. Sloan,

1977. Natural regulation of

innocuous gypsy moth populations.

Environ. Entomol. 6:315-322.

Chapman, E M. 1968. The warblers

of North America. Dover Publishing

Co., New York.

DeGraaf, R. M, H. R. PyweU, and J.

W. Thomas. 1975. Relationships

between nest height, vegetation, and

housing density in New England

suburbs. Trans. Northeast Sect.

WUdl.Soc. 32:130-139.

70
Forbush, E. H., and C. H. Fernald.

18%. The gypsy moth. Wright and

Potter, Boston.

Furuta, K. 1976. Studies on the

dynamics of the low density

population of gypsy moth and todafir aphid (in Japanese, English

summary). Jap. Gov. For. Exp. Stn.

BuU. 279. Tokyo.

Galipeau, P. R. 1975. Avian

predators of the gypsy moth.

Unpublished report. U.S. Dep.

Agrie. For. Serv., Northeast. For.

Exp. Stn., Hamden, Conn.

Garlo, A. S. 1977. Personal

communication. U.S. Dep. Agrie.

For. Serv., Northeast. For. Exp.

Stn., Hamden, Conn.

Hamilton, W. J., and D. B. Cook.

1940. Small mammals and the

forest. J. For. 38:468-473.

Holmes, R. T., and E W. Sturges.

1975. Bird community dynamics

and energetics in a northern

hardwood ecosystem. J. Anim.

Ecol. 44:175-200.

Lautenschlager, R. A., H.

Rothenbacher, and J. D. Podgwaite.

1978. The response of small

mammals to aerial applications of

the nucleopolyhedrosis virus of the

gypsy moth, Lymantria dispar.

Environ. Entomol. (In¡press.)

Lewis, F. B. 1978. Personal

correspondence. U.S. Dep. Agrie.

For. Serv., Hamden, Conn.

Mosher, E H. 1915. Food plants of

the gypsy moth in America. US.

Dep. Agrie, Bull. No. 250.

ODeU, T. M. 1977. Personal

communication. U.S. Dep. Agrie.

For. Serv., Hamden, Conn.

Palmer, E. L., and H. S. Fowler.

1975. Fieldbook of natural history.

McGraw-Hill, New York.

Paszek, E. C. 1977. Personal

communication. U.S. Dep. Agrie.

Anim. Plant Health Insp. Serv., Otis

AFB, Mass.

Reardon, R. C. 1976. Parasite

incidence and ecological

relationships in field populations of

gypsy moth larvae and pupae.

Environ. Entomol. 5:981-987.

Rotschild, E. V. 1958. Extermination

by rodents of the gypsy moth in an

area of mass reproduction. (Trans,

from Russian.) Byull. Mosk. O-VA.

Ispyt. Prir. Otd. Biol. 63:129-130.

Smith, D. M. 1978. Personal

communication. Yale Univ. Sch.

For. Environ. Stud., New Haven,

Conn.

Smith, H. R. 1975. Management of

Peromyscus leucopus as part of an

integrated program to control the

gypsy moth Trans. Northeast Sect.

Wildl.Soc. 32:111-130.

Smith, R. E 1%9. Integrated control

of insects—challenge for scientists.

Agr. Sei. Rev. 7(1): 1-5.

Swan, L. A., and C. S. Papp. 1972.

The common insects of North

America. Harper and Row, New

York.

71
Tinbergen, L. 1%0. Dynamics of Watt, K. E. F. 1968. Ecology and

insect and bird populations in pine resource management. McGrawwoods. Arch. Neth. Zoo. 13:265- Hill Book Co., New York.

343. Welty, J. C. 1%2. The life of birds.

Trippensee, R. E. 1948. WUdlife W. B. Saunders Co., Philadelphia.

management: Upland game and

general principles, vol. 1. McGrawHiU Book Co., New York.

T\ircek, F. J. 1952. An ecological

analysis of the bird and mammalian

population of a primeval forest on

the Polona-mountain (Slovakia).

Bull. Int. de I'Acad. tchèque Sei.

53:1-25.

Issued December 1978

Available from the Superintendent of

Documents

U.S. Government Printing Office

Washington, D.C. 20402

Stock No. 001-000-03851-6

72 it as. GOVERNMENT PRINTING OFFICE : 1978 O—273-078