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Spongy Moth Destruction

Have you been in woods lately? Have you heard what almost sounds like rain hitting the leaves above your head? I hate to be the bearer of bad news, but that’s not a passing summer shower. What you are hearing are Spongy moths, and their munching is doing a number on our local forests and trees.

Spongy moth (Lymantria dispar dispar) — formerly known as gypsy moth — is a serious forest pest and is responsible for killing millions of oak and other species of trees across the state.

The name change comes courtesy of the Entomological Society of America (ESA). The former name was removed from the agency’s Common Names of Insects and Related Organisms List because it included “gypsy,” an offensive term for the Romani people. The alteration is part of the organization’s Better Common Names Project.

As reported by the ESA, “The name — derived from the common name used in France and French-speaking Canada, ‘spongieuse’ — refers to the moth’s sponge-like egg masses.

“Lymantria dispar is a damaging pest in North American forests, and public awareness is critical in slowing its spread. ‘Spongy moth’ gives entomologists and foresters a name for this species that reinforces an important feature of the moth’s biology and moves away from the outdated term that was previously used,” says ESA President Jessica Ware, Ph.D. “We are grateful to the diverse community of people and organizations who have been involved in this renaming process and have committed to adopting ‘spongy moth’ as well.”
About the Insect

As explained by Penn State Extension, “Fuzzy, felt-like, tan egg masses laid by females during the prior adult mating season contain hundreds of eggs per mass and are often found attached to tree trunks, in sheltered branch locations, and on many other outdoor structures. Larvae hatch from early April to late May, usually climbing the same tree where their egg mass is located to feed or blowing on silk strands to neighboring stands of trees. Caterpillars feed on foliage and molt several times as they mature. Mature caterpillars are distinctive in appearance, with five pairs of blue spots six pairs of red spots running down the body. In late June or early July, caterpillars pupate, emerging as winged adults a few weeks later.”

The Spongy Moth was accidentally introduced into Massachusetts in 1869 by a French scientist trying to find a disease-resistant caterpillar to increase the output of silk. Since first being detected in Pennsylvania in Luzerne and Lackawanna counties in 1932, the spongy moth has wreaked havoc on Pennsylvania’s forests, killing millions of oak trees along the way.

A prime way the spongy moth spreads is via egg masses when transported on firewood, outdoor equipment, and vehicles. Public awareness of the moths’ egg masses and its sponge-like appearance is important in controlling the pest, as the insect spends most of its life cycle (10 months) in the egg stage.

As you can see by the picture on the cover, (Thank you to Laura Jansen for letting me steal her picture) our area hasn’t been spared in the spongy moth destruction. If you are familiar with the Hyner area, you can easily see how many trees have fallen victim.

Although oak species are preferred, spongy moth caterpillars feed on hundreds of other tree and shrub species, including:
– Apple
– Alder
– Aspens
– Basswood
– Birches
– Hawthorn
– Hemlock
– Tamarack (larch)
– Pines
– Spruces
– Willows
– Witch hazel

According to the Pennsylvania Department of Conservation & Natural Resources (DCNR), “It usually takes more than one year of defoliation before trees die; however, conifers that are defoliated may be killed after a single season of defoliation.

“Although the boom and bust cycles of the spongy moth are less severe than during the past, they still require control during years when their populations are high.”

The spongy moth has been causing substantial forest damage here since the 1970s. The most recent occurrence occurred from 2013 to 2019 and another outbreak occurred from 2021 through 2022.

This pest has been a primary cause of tree mortality on state forest land since the 1970s.

According to the state Bureau of Forestry, in 2014, the moths defoliated 214,972 acres across the commonwealth. That was a decrease from 1991, when the insects stripped bare 4 million acres of woodland.

We can all help the situation in our own backyards though.

Take a look around your property for egg masses in the summer and fall. The spongy moth has one generation per year in Pennsylvania.

Females lay their eggs as light tan egg masses (100-1,500 eggs/mass) on trees, stones, and other substrates during June and July. So now is the time.

Eggs hatch from mid-April to early May the following spring.

What do you do if you find spongy moth eggs on your property? DNCR says the following:

“Tactics for mechanical removal of spongy moth egg masses can be effective for individual yard trees, but are not effective as a forest-wide control method.

“Methods include removal of egg masses before they hatch and removal of unnecessary yard objects where egg masses can be hidden, such as:
– Piles of old wood
– Building materials
– Dead branches, firewood, and other refuse

“Egg masses should be scraped into a sealed container or bag and disposed.

“Another control tactic is wrapping burlap around the trunks of trees where spongy moth larvae can hide during the day.

“The larvae hiding under the burlap are then scraped into a can of soapy water, killing the larvae.”

Insecticides can help, but they do not get rid of spongy moths entirely, so you’ll have to use your own discretion to decide on that. Insecticides are not necessary unless the population of spongy moth egg masses or larvae indicate a threat to your trees.

DCNR notes that they conduct an aerial spongy moth suppression program to treat state and federal forest lands, but they do not spray for spongy moths on private lands.

Private landowners or municipalities can conduct their own treatment program by following the steps in the “Guide to Conducting a Private Spongy Moth Suppression Program” which is available on their website (

According to the PA Game Commission, “Spongy moth is a destructive, invasive insect and not part of Pennsylvania’s natural ecosystem. Historically, spongy moth impacts have been devastating to the oak dominated forests in Pennsylvania. Massive amounts of oak mortality have led to rapid stand conversions to less desirable forest types across tens of thousands of acres at a time. This can lead to a much lower quality habitat for species ranging from native insects to large mammals, such as deer. Protecting oak habitats with a spray program can also allow for more regular acorn crops now and into the future.”

So much like the Spotted Lanternfly, if you see the egg masses, please follow the steps above and get rid of them.