Spongy moths could cause extensive tree defoliation this year

by Kate Evans

Some Morgan County residents are reporting high numbers of spongy moth egg masses this year  after last year’s deluge of caterpillars, pupae and adult moths that caused tree defoliation.  The spongy moth (Lymantria dispar) was formerly known as the gypsy moth.

West Virginia officials are concerned about possible tree mortality, disease from tree stress, deforestation and defoliation that could occur from the spread of the spongy moth without treatment to infested properties.

Scott Hoffman, West Virginia Department of Agriculture Gypsy Moth Cooperative Suppression Coordinator, said last year that they saw a lot of defoliation in Morgan County from the spongy moths-mainly on Cacapon Mountain and in Great Cacapon. In some areas the defoliation was heavy while other areas had lighter damage.

Hoffman expected this year’s spongy moth population to be much higher in Morgan County and the damage to be much worse.

Last year and this year they checked areas that included Cacapon Mountain, Sideling Mountain and Sleepy Creek Mountain, Hoffman said.  Caterpillar infestations and tree defoliation were seen in those areas last year.  They’ve counted high numbers of egg masses in those areas this year.  The larvae will be starting to hatch from the eggs masses in the higher elevations with the warmth and rain.  Other areas will follow in mid to late April.

The spongy moth larvae are very tiny when they first hatch-around 1/ 4 inch. They go through around five or six instars as  larvae.  They don’t become actual moths in the adult stage until around July, Hoffman said..

Last year they saw some caterpillars that had the Nucleopolyhedrosis Virus (NPV) and the Entomophaga maimaiga fungus,  but they had very little collapse of the spongy moth population collapse from either due to not getting enough rain, Hoffman said. Both the virus and the fungus are present in nature but they need rain and warm weather to proliferate.

If the population doesn’t collapse this year from the virus and the fungus, there will be a lot of defoliation this year since there’s a pretty high population of spongy moths, Hoffman said. But recent rains along with more rain events could push a population collapse this year so the spongy moths wouldn’t be a problem next year.


The spongy moth caterpillars feed on hundreds of different trees and shrubs, causing valuable timber loss and impacting wildlife, habitat and recreation.  Their preferred tree of infestation is oak, but they also attack most other hardwoods like beech, birch, elm, willow, maple, polar,  sweetgum and basswood.

Spongy moth caterpillar eating a sassafras leaf.

Hoffman said spongy moths like oak-hickory types of forests.  If there’s a high population, they’ll feed on other less desirable trees like hemlock, pine and spruce.

Repeated heavy defoliation by the insect kills trees.  The mortality of hardwood trees after two successive years of defoliation can reach 80%.  Trees can also be affected by other pests and diseases since they are weakened.


The Nucleopolyhedrosis Virus (NPV) occurs naturally in spongy moth populations and spreads through caterpillar contact during outbreaks, causing a population crash. Dead caterpillars hanging from tree trunks and other items in an upside-down “V” formation indicates NPV infection.

The Entomophaga maimaiga fungus remains in the soil and infects the caterpillars that come into contact with its spores, according to the Michigan Department of Natural Resources.  Moist soil helps to activate the fungus.  Caterpillars infected with the E. maimaiga fungus stay attached to tree trunks but hang straight down.


There are some natural predators of spongy moths, but they don’t have a lot of effect on their populations, Hoffman said previously. Many birds prey on the spongy moth caterpillars, adults and/or their egg masses and help decrease their populations.

Predatory birds include the black-capped chickadee, tufted titmouse, white-breasted nuthatch, starling, common grackle, Eastern bluebird, the American robin, phoebe, blue jay, downy woodpeckers, brown thrasher, Baltimore orioles, American crow, grey catbird, house wren, red-winged blackbird, Eastern towhee, chipping sparrow, indigo bunting,   flicker,  rose-breasted grosbeak, yellow-billed cuckoo and scarlet tanager.

Mice, shrews, chipmunks,  skunks, raccoons and squirrels will also feed on spongy moth caterpillars and pupae on the ground and at the base of trees.

Things to do

Hoffman advised landowners to collect egg masses on trees they want to protect.  Hanging folded-over burlap or cloth on trees with baling twine will give the caterpillars a place to collect and turn into pupae. Female spongy moths will also lay their eggs there.

Scrape the egg masses off the tree bark and squish them, Hoffman said. If you see the larvae (caterpillars), the females are bigger.  He recommended smashing them.

The Spongy Moth life cycle and timeline is displayed in this pictorial chart. The spongy moth was formerly known as the Gypsy Moth.
Photo courtesy of the West Virginia Department of Agriculture.

Each female you kill before it can lay eggs will keep 250-500 larvae from feeding on your trees the next year, Hoffman said.   People can also use a contact insecticide labeled for spongy moths. save you a lot of trouble next year,

Hoffman said that egg masses the size of a dime mean that the spongy moth population could be declining and isn’t very healthy.  Long, large egg masses could indicate that the population is building.

Suppression Program

Hoffman encouraged landowners to register for the Gypsy Moth Cooperative Suppression Program to help slow the spread of the insect.  Adjacent landowners can join together and combine their properties to meet the acreage requirement for aerial spraying, Hoffman said.  There is a minimum requirement of 50 acres of wooded land per block.

Some 2,861 acres in Morgan County were sprayed in May, 2023 for gypsy moth-mostly on Cacapon Mountain and in Great Cacapon, Hoffman said.  The acreage sprayed included state land, private lands or developments.

Hoffman said he has 30-35 landowners registered for aerial spraying this spring.  Spraying could begin the last week of April but more likely will take place in May.  The spraying will be done by large military-like Huey helicopters that are very loud.


Sign-ups are being done in July and August for spraying next year.  $1.00 an acre survey deposit, up to $500,  must be submitted with the application.

Once applications are received,  Department of Agriculture personnel will come out to conduct an egg mass survey and check your property to see if it qualifies for spraying, Hoffman said.   Areas with 500 egg masses per acre or more that are wooded residential, wooded recreational, or non-residential woodlands can be designated for possible treatment.

Spraying choices

They offer two different spraying product choices-Bacillus thuringiensis var.kurstaki (Btk) and Mimic (Tebufenozide), he said. Btk is considered safe in regards to humans and animals. Mimic has low toxicity to other insects and animals.   A lot of landowners that used Btk before are now using Mimic for greater persistence in eradicating egg masses. Btk gives foliage protection.

Hoffman said no additional landowners could be added now for aerial spraying this spring since there’s a long process involved with permitting through the West Virginia Department of Environmental Protection, the Division of Natural Resources, the Division of Forestry and Fish and Wildlife.  A landowner could opt to have their aerial spraying done privately this year.

Other counties, states

Aerial sprayings have been done in a few Berkeley County blocks and a lot of Morgan County blocks, Hoffman said.  Treatments have also been done in Hampshire, Grant and Hardy Counties. Surrounding states are doing similar aerial spraying measures like West Virginia’s.

The spongy moth cooperative suppression program hopes to slow the spread of the pest into non-infested areas of the state, to suppress spongy moth populations in infested areas and to limit tree defoliation and mortality as much as possible, according to the West Virginia Department of Agriculture. (WVDA)

Applications are available on the WVDA website, at local West Virginia University Extension Offices and also through the WVDA Charleston and New Creek offices.

For more information, contact WVDA Assistant Director Quentin “Butch” Sayers at or WVDA Gypsy Moth Program Coordinator G. Scott Hoffman at 304-788-1066.