Gypsy Moth & 

Management

Table of Contents

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Quarantine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Identifi cation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3

Is Gypsy Moth a Threat to My Trees? . . . . . . . . . . . . . . . . . . . . . . . .6

Managing Gypsy Moth

Predicting Tree Damage from Gypsy Moth. . . . . . . . . . . . . . . . .7

Quick Predictive Survey Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Physical Controls for Yard Trees . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Biological Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Controls for Woodlots and Insecticide Options

for Yard Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Aerial Insecticidal Control for Large Acreages . . . . . . . . . . . 13

Contacts & Further Information . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

The Wisconsin Cooperative Gypsy Moth Program consists of partners from:

➤ Department of Agriculture, Trade, and Consumer Protection

➤ Department of Natural Resources 

➤ University of Wisconsin – Extension

DATCP manages a program called Slow the Spread (STS) that aims to eradicate small, isolated 

populations of gypsy moth in non-quarantined counties in Wisconsin. DNR works with local 

governments to conduct spraying of residential and wooded areas where gypsy moth populations 

are rising to levels that could cause defoliation. UW - Extension provides public education.

The Wisconsin Department of Natural Resources provides equal opportunity in its employment, 

programs, services and functions under an Affi rmative Action Plan. If you have any questions, 

please write to: Equal Opportunity Offi ce, Department of the Interior, Washington, D.C. 20240. 

This publication is available in alternative format (large print, Braille, audiotape, etc) upon request. Please 

call 1-800-642-6684 and select the menu option to speak with a DNR staff member to place your request. Landesforstpräsidium Sachsen Archive, Bugwood.org USDA APHIS PPQ, Bugwood.org

1

Introduction

The gypsy moth is a foreign 

pest that was introduced 

to Massachusetts in 1869. 

Since then, it has moved 

south and west and has 

become a signifi cant pest 

of forest and shade trees. 

Gypsy moth populations 

naturally explode to very high 

numbers, called outbreaks, 

about every 10 years. During 

outbreaks, the caterpillars are 

a nuisance and can strip trees 

of their leaves, defoliating 

entire neighborhoods or forests 

by late June. Most healthy 

trees can survive one such 

defoliation, but trees that 

are weak or stressed prior 

to defoliation may die.

The gypsy moth was detected 

in Wisconsin in the 1990s and 

as of 2008 is fi rmly established 

throughout the eastern and 

central part of the state. 

Eventually, it will become 

established across the entire 

state. Gypsy moth will never 

be eradicated from Wisconsin 

but its populations can be 

managed, minimizing the 

damaging effects of outbreaks.

How it Spreads 

The gypsy moth is an 

expert at hitching rides and 

establishing new populations 

in areas previously free 

from infestation. Just about 

anything you would fi nd in 

your backyard or woodlot, 

even your vehicle, can be a 

suitable place for the female 

moth to lay her egg mass. Egg 

masses and caterpillars can 

easily be moved to another 

location across town, across 

the state, or across the country, 

creating the likelihood of 

a newly infested area. 

Dr. J.A. Davidson, University of Maryland, College Park
2

Gypsy Moth Quarantine 

To help prevent the spread of 

gypsy moth, state and federal 

regulations require that all 

outdoor items being moved 

from an infested area into a 

non-infested area be inspected 

to ensure that they are free of 

gypsy moth in any life stage. 

To determine if you are in a 

quarantine county, please visit 

http://gypsymoth.wi.gov.

For more information on 

quarantine regulations 

pertaining to households, 

nurseries, and fi rewood, 

visit http://gypsymoth.wi.gov 

and link to “Don’t Move 

Gypsy Moth - DATCP 

Quarantine Details.” You can help prevent the 

spread of gypsy moth. If you 

live in an area where gypsy 

moth is established, check 

vehicles or outdoor items for 

egg masses before moving 

them to unquarantined areas.

Firewood is a favorite hiding 

place for gypsy moth. Be 

especially vigilant during and 

after an outbreak when egg 

masses will be abundant.

Dr. Francis Eugene Wood, University of Maryland, College Park

Andrea Diss, WI DNR
3

male female

Actual size of pupa

Identifi cation

Larva (Caterpillar)

In Wisconsin, gypsy moth 

larvae (caterpillars) are 

present from May through 

mid-July. They can be hard 

to identify when they are 

small, but by June they 

are large enough to see 

distinctive features.

The caterpillar is bristly 

and has two rows of colored 

“warts” running the length 

of its back. There are blue 

warts near the head and red 

warts near toward the rear. 

The head is yellowish and has 

two vertical black stripes.

Gypsy moth caterpillars can 

also be identifi ed by their 

behavior. Starting 

in June, when they 

are about 3/4 of an 

inch long, they 

crawl out of the 

tree canopy during 

the day to look for 

hiding places to 

rest. You may fi nd 

them resting on 

the trunk of the 

tree or on nearby 

buildings or other 

outdoor surfaces. 

Pupa

Gypsy moth caterpillars 

complete their growth by 

late June to mid-July, then 

pupate to transform into 

an adult moth. The pupa 

has a hard outer shell 

to protect it during the 

transformation. The process 

takes approximately two 

weeks. Male caterpillars 

pupate earlier than 

females and 

their pupae 

are smaller.

Actual size

in early June

Actual size

in late June 

and early July

Dr. J.A. Davidson, University of Maryland, College Park

Dr. J.A. Davidson, University of Maryland, College Park Dr. J.A. Davidson, University of Maryland, College Park
4

Egg Mass

The gypsy moth 

egg mass is the 

easiest life stage 

to fi nd during 

most of the year. 

They are present 

from August until 

the following May. 

Egg masses are slightly oval 

and range in size from 3/4 of 

an inch to two inches long.

Each mass may contain up to 

1,000 individual eggs. An egg 

mass produced in the current 

season is fi rm to the touch, 

covered with tiny hairs, and 

colored a light tan to golden 

yellow. Egg masses from 

previous years are bleached 

white to pale yellow, are soft 

and spongy, and tattered.

Egg masses can be found 

just about anywhere. They 

can be found on logs or 

debris on the forest fl oor or 

on the uppermost branches 

of trees and anywhere in 

between. Female moths will 

also deposit egg masses on 

fi rewood piles, lawn furniture, 

play sets, houses and other 

human-made structures. 

Moth

In Wisconsin, the gypsy moth 

adult starts emerging in July 

and may be observed into 

September in the north. The 

female moth is white with 

small V-shaped markings on 

her wings. Although she has 

wings she cannot fl y. She gives 

off a pheromone to attract 

male moths who come to her. 

The male gypsy moth is 

smaller than the female, 

brown with large, feathery 

antennae. They are similar 

to several native moths. A 

distinguishing feature is that 

the male fl ies during the day 

searching for female moths. 

Clouds of male moths can be 

seen fl uttering at sites where 

females are concentrated. 

Adult moths do not 

eat; they mate and die 

within two weeks.

Actual size

Actual size

Male

Female

Illustrations by Cooperative Extension Service, University of Maryland System
5

It’s NOT a Gypsy Moth If

➤ It’s a moth in the spring 

or early summer

➤ It’s a caterpillar in 

the late summer

➤ It’s building a silk nest or 

tent with other caterpillars

➤ It’s not hairy and it doesn’t 

have blue and red spots 

on the caterpillar’s back.

Eastern Tent Caterpillar 

➤ dark brown or 

black with a pale 

yellow stripe 

running the length 

of the body and 

blue and white 

spots on side

➤ most often 

found on cherry, 

crabapple and 

apple trees 

in spring

➤ builds a dense 

silk tent in the crotch 

or a branch fork of a 

tree in the spring

➤ may cause defoliation, but 

is seldom a serious threat 

Forest Tent Caterpillar

➤ black stripe down 

back, a row of 

white or pale 

yellow keyholeshaped markings 

down the center 

of the stripe

➤ sides are sky blue

➤ does not 

construct a silk 

tent, but makes a 

“mat” that may 

be seen on trees

➤ outbreaks occur in spring 

about every 10 years in 

parts of the northern 

third of Wisconsin 

Fall Web Worm

➤ appear late in 

the summer 

and early fall

➤ constructs a 

large, loosely 

woven silk web 

at the outer 

edge of the 

tree canopy.

➤ nests may 

be found on 

many hardwood trees 

including birch, willow, 

walnut, and hickory

➤ can be an eyesore, but 

rarely threatens the tree

USDA

Illustrations by Dr. J.A. Davidson, University of Maryland, College Park

Gypsy moth caterpillar
6

Is Gypsy Moth a 

Threat to My Trees?

In most years the answer to 

this question is no. Gypsy 

moth is only a threat to your 

trees when its population 

increases to very high 

numbers, called an outbreak. 

Outbreaks occur in cycles, 

about every ten years or so in 

most areas where gypsy moth 

is established. You can predict 

an outbreak up to nine months 

before it starts by making 

some simple observations. This 

allows plenty of time to take 

action to prevent defoliation 

and damage to your trees. 

In June and July, be on the 

lookout for gypsy moth 

caterpillars coming out of 

the trees to rest on tree trunks 

and the sides of buildings. 

The presence of caterpillars 

– even in small numbers – may 

indicate that a population is on 

the rise and could be a bigger 

problem next year. Starting in 

August, look for gypsy moth 

egg masses. The number of egg 

masses is a good indicator of 

the number of caterpillars to 

expect in your area next spring.

Keep in mind, healthy trees 

will recover from a defoliation. 

Trees that are weak from 

drought, previous defoliation, 

age or other stressors may 

not survive unless they are 

protected from gypsy moth. 

What Does the Gypsy 

Moth Caterpillar Eat?

Gypsy moth caterpillars can 

feed on about 500 different 

kinds of trees and shrubs. 

Preferred: oak, aspen, 

willow, apple and 

crabapple, tamarack, 

white birch, witch hazel, 

mountain ash, basswood, 

ironwood, and linden 

Acceptable: maple, walnut, 

chestnut, hickory, cherry, 

hemlock, elm, hackberry, 

yellow birch, beech, 

cottonwood, box elder, 

and ironwood . . . older 

caterpillars may also 

eat pine and spruce

Seldom: green, white or black 

ash, balsam and fraser 

fi r, locust, scotch pine, red 

cedar, tulip poplar, catalpa, 

sycamore, and dogwood
7

Predicting Tree Damage 

from Gypsy Moth

In the fall, take a walk 

around your woodlot or 

neighborhood. If you don’t see 

any egg masses or only a few 

within a ten minute walk, it is 

unlikely that the population 

will be high enough to cause 

defoliation next year. However, 

be aware that if you see 

some egg masses you should 

monitor again next year as the 

population may be increasing. 

If you see egg masses 

regularly on your walk, you 

should consider doing a few 

1/40th acre surveys to get a 

better idea of whether you 

will have defoliation from 

gypsy moth next year.

Complete instructions on 

how to do a 1/40th acre 

predictive survey can be found 

at http://gypsymoth.wi.gov.

Quick Survey Guide

➤ Measure rope 

18 feet 6 inches

➤ Stake one end of the rope 

and with the other end 

“draw” a circle around a 

typical piece of your property 

➤ Count all new egg masses 

you can fi nd in that circle

➤ The gypsy moth population 

is predicted to be a 

nuisance and cause heavy 

defoliation if you see: 

➤ An average of 13 or more 

egg masses per circle 

in residential areas 

➤ An average of 25 or 

more egg masses per 

circle in woodlots

➤ Check the Web for 

complete instructions

18-foot-6-inch piece of rope
8

If you plan to participate in 

the state aerial suppression 

program, you should oil 

egg masses and then leave 

them alone. Surveyors 

will need to count the egg 

masses on your property 

to determine if the area 

qualifi es for participation.

Beginning in October,

manage egg 

masses in either 

of two ways:

#1 Spray them with 

a horticultural oil 

labeled for gypsy moth

➤ Horticultural oil 

suffocates the eggs

➤ it is formulated to penetrate 

the mass of hairs and coat 

the eggs thoroughly. 

➤ it requires a couple weeks 

to completely suffocate the 

eggs . . . do not use this 

technique after the middle 

of April since it might not 

kill all the caterpillars 

before they hatch 

Managing Gypsy Moth: 

Physical Controls 

for Yard Trees 

Managing gypsy moth in your 

backyard changes throughout 

the year as the moth develops 

through its lifecycle.

Lifestage: Egg Mass

The gypsy moth egg mass is 

present in Wisconsin from 

August until May. Each egg 

mass you destroy prevents 

several hundred caterpillars 

from hatching in the spring. 

The female gypsy moth will 

lay her eggs on any surface 

so it’s important that you 

inspect your entire yard. 

Wait until after the fi rst 

hard frost before destroying 

egg masses by either of the 

two methods. There are 

natural enemies of the gypsy 

moth that will attack the 

eggs . . . a benefi t to you!

There are two factors to 

consider before deciding 

which option to use

➤ the time of year

➤ whether you live in a 

potential “suppression 

spray” area

October
9

Lifestage: Young Caterpillar

By late April, place 

a sticky barrier 

band on each tree 

trunk (about waist 

high) to help 

prevent caterpillars 

from climbing into the 

tree. Bands can be bought 

or made using duct tape 

(silver side out) around a 

tree trunk and coated with a 

horticulture grade sticky trap 

material, available at most 

lawn and garden centers. 

➤ Never put the sticky 

trap material directly 

on the tree trunk

➤ On thin-barked trees such as 

birch, place a layer of paper 

bags around the trunk 

before using the duct tape.

➤ Sticky material may 

need to be re-applied

➤ Collect and kill any 

caterpillars at the 

base of the tree 

➤ Never use automotive 

greases on trees. 

It can kill them.

Or

#2Scrape them off and 

kill the egg masses 

➤ kill eggs by placing 

them in a container and 

microwaving them on 

high for two minutes or

➤ drown them in soapy 

water for two days

➤ killed egg masses may be 

thrown out in the trash 

➤ don’t merely scrape the 

egg masses to the ground. 

They will still survive and 

hatch in the spring!

Sticky barrier and collection 

bands work well when 

populations of gypsy moth 

caterpillars are low to 

moderate. In outbreaks, 

these methods will 

have limited results.

April

Don’t handle caterpillars or egg masses 

with your bare hands. The gypsy moth’s hair 

often causes a mild allergic reaction. Wear 

gloves or use a putty knife to handle them.

Illustration by Cooperative Extension Service, Univ. of Maryland System
10

Lifestage: Pupa & Moth

In July, begin 

inspecting all 

outdoor surfaces 

in your backyard 

for gypsy moth 

pupae. The pupa is 

a brown shell, often attached 

to tree bark or other surfaces 

with strands of fi ne silk. 

➤ Those in reach are easily 

destroyed by crushing

➤ Crush those that are out of 

reach with an extendable 

pole or dislodge them with 

water from a garden hose 

and destroy those that 

fall to the ground

The female moth is 

also an easy target 

for control. Since 

it can’t fl y, crush 

those that you fi nd 

on your property.

Avoid directly touching female 

moths as their pheromone will 

get onto you and you will be 

mobbed by male moths.

Each female moth 

eliminated before it 

produces an egg mass will 

prevent the emergence of 

several hundred caterpillars 

the following spring.

Lifestage: Older Caterpillar

In early June, add 

a cloth or burlap 

collection band 

above the sticky 

barrier (about 

chest high). 

Collection bands can be made 

from heavy dark cloth or 

burlap that’s approximately 

12-18 inches wide and 

long enough to completely 

wrap around the tree.

➤ Tie a piece of twine 

around the middle 

of the cloth band

➤ Fold the top half of the 

cloth down over the twine 

to cover the bottom half

➤ Caterpillars are attracted 

to these “skirts” when 

looking for a place to 

hide during the day

➤ Destroy caterpillars 

each afternoon by 

scraping them into a 

container of soapy water 

or snipping them in half

June

July

Dr. J.A. Davidson, University of Maryland, College Park

A word About Gypsy Moth Traps . . . 

Over-the-counter pheromone 

traps available at garden 

centers or from the Internet kill 

only males and are not helpful 

in reducing outbreaks. They 

are more helpful in detecting 

gypsy moth in areas where 

populations are very low. 
11

Biological Controls

Natural enemies can help 

moderate gypsy moth cycles. 

Native predators can delay 

outbreaks and specialist 

diseases often end outbreaks. 

The DNR has introduced 

specialist parasites and 

diseases to bring the gypsy 

moth into a more natural 

balance. These are now 

established over the range of 

gypsy moth in Wisconsin. For 

images of these allies, go to 

http://gypsymoth.wi.gov and 

link to biological controls. 

Our most important native 

predator is the deer mouse 

which attacks caterpillars and 

pupae. Where deer mice are 

excluded by mowing under 

oaks, gypsy moth populations 

increase to defoliating levels 

sooner than in stands where 

there is natural undergrowth. 

Encourage deer mice to 

patrol your oaks by underplanting them with shrubs 

and other plants that provide 

cover from cats and owls.

Ooencyrtus kuvanae is a tiny 

wasp that parasitizes the 

eggs of gypsy moth. While it 

is hard to see this gnat-sized 

wasp, you can see the pinholes it left when exiting new 

egg masses in early fall. If 

you wait to oil or remove egg 

masses until after a hard frost, 

this tiny insect will repay you 

by killing eggs higher on the 

tree than you can reach!

Two diseases typically end 

outbreaks. Entomophaga 

maimaiga, a fungus, is 

most effective when the 

weather is wet in May 

and June. Gypsy moth 

nucleopolyherdrosis virus 

(NPV) kills caterpillars that 

are weak due to starvation 

or other factors. Both of these 

only effect gypsy moth.

Andrea Diss-Torrance, WI DNR
12

Controls for Woodlots 

(many trees)

The key to managing gypsy 

moth in woodlots is to 

maintain a healthy forest. 

If trees are healthy they are 

able to recover from a single 

year of heavy defoliation. 

Proper spacing will keep trees 

growing steadily at a moderate 

pace. Such trees are better 

able to rebound from stress, 

including defoliation. Trees 

are more likely to die after 

a single defoliation if they 

are crowded or unhealthy. 

Tree species preferred by 

gypsy moth will always be 

defoliated more severely 

during outbreaks than those 

that are less favored. In 

deciduous stands, you should 

maintain a mix of favored 

and less favored species. This 

will reduce losses and help 

reduce the secondary effects of 

defoliation of all the trees in a 

stand. These secondary effects 

include increased runoff, loss 

of cover, and reduction of 

food for birds and animals. 

Continue to maintain oaks in 

your stand where appropriate 

as gypsy moth is only one of 

the pests and diseases that 

attack trees in our area. 

There will be situations where 

a woodlot owner may want 

to use a suppression spray 

to prevent defoliation of the 

stand. If the trees are stressed 

due to a recent drought, none 

may be in condition to recover 

from the additional stress of 

defoliation. Recently planted 

and young oaks may also 

need protection from a gypsy 

moth outbreak to survive. 

Woodlot management with 

gypsy moth in mind can be 

complicated and may require 

the services of a professional 

forester. For additional 

information, consult the 

DNR publication Gypsy 

Moth Silvicultural 

Guidelines for Wisconsin, 

visit http://gypsymoth.wi.gov, 

call 1-800-642-MOTH (6684), 

or email dnrfrgypsymoth@

wisconsin.gov

Insecticide Options 

for Yard Trees

There are many insecticides 

available to control the gypsy 

moth in your backyard. 

When selecting a pesticide, 

some things to consider are:

➤ Presence of young 

children or pets

➤ Proximity to water 

resources (stream, 

decorative pond, etc.)

➤ Presence of other 

desirable insect species

➤ Nearby vegetable 

or fruit gardens
13

Most available insecticides are 

used by spraying them onto the 

tree’s leaves. If general exposure 

(through spraying) is an issue, 

you might consider systemic 

application. A systemic 

approach applies pesticide 

directly into the tree through 

injections or into the ground 

around it where it is taken up 

by the roots. Older trees might 

show less response to a systemic 

application than younger ones. 

For a list of pesticides for 

gyspy moth control, visit 

http://gypsymoth.wi.gov and 

link to “Pesticide Information.”

Unless your trees are 

relatively small – less than 

about 12 feet tall – you 

will likely need to hire an 

arborist or certifi ed pesticide 

applicator to thoroughly 

and safely treat your trees. 

You may fi nd one through 

the Wisconsin Arborist 

Association’s Web site 

at www.waa-isa.org.

Aerial Insecticidal 

Control for Large 

Acreages 

. . . on Property of 

20 Acres or More

The Wisconsin Department 

of Natural Resources offers 

a Gypsy Moth Suppression 

Program to counties to 

suppress gypsy moth 

outbreaks. This voluntary, 

aerial insecticide program 

focuses on reducing high 

populations of the pest 

to tolerable levels that do 

not threaten the trees.

Participation in the 

Suppression Program increases 

access to aerial spraying in 

residential areas. The USDA 

Forest Service may share 

the expense of these aerial 

treatments along with the 

associated administrative costs.

County offi cials initiate and 

coordinate the program with 

assistance from the DNR. 

Participating counties provide 

a local coordinator who acts 

as a contact for both the 

J. Maentanis
14

public and the DNR, and is 

responsible for a number of 

duties at the local level. To 

apply for the suppression 

program, landowners 

should contact their county 

government offi cials or 

gypsy moth coordinator. 

Contact information is 

available through the 

DNR Suppression 

Spray Program link at 

http://gypsymoth.wi.gov. 

Areas proposed for treatment 

are determined in autumn. 

Applications are due from 

counties by early December.

The treatment methods 

employed during the 

spray season include 

a formulation of the 

bacterial insecticide Bacillus 

thuringiensis kurstaki (Btk) 

or, if endangered butterfl ies 

or moths are present, 

Gypchek, a viral insecticide 

that specifi cally targets 

gypsy moth caterpillars. 

The aerial suppression 

program is an option 

primarily in those Wisconsin 

counties that have been 

quarantined for gypsy moth. 

To get the latest information 

regarding the gypsy moth 

suppression program, visit 

http://gypsymoth.wi.gov, 

call the toll-free gypsy 

moth information line at 

Dr. J.A. Davidson, University of Maryland, College Park

1-800-642-MOTH (6684), 

or email dnrfrgypsymoth@

wisconsin.gov. 

Whether or not the county 

or community chooses to 

participate in the voluntary 

suppression program, 

property owners also have 

the options of arranging for 

a private spray. For guidance 

on how to do this, visit 

http://gypsymoth.wi.gov.

Contacts & Information

On the Web

http://gypsymoth.wi.gov

DNR Gypsy Moth Email: 

dnrfrgypsymoth@wisconsin.gov

Gypsy Moth Information Line:

1-800-642-MOTH (6684)

This booklet is also available 

online to download 

and print by section at 

http://gypsymoth.wi.gov