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The Spongy Moth’s Storied Origin

By Jennifer Correa-Kruegel, Warren County Naturalist

April 22, 2026

Spongy moth caterpillar on a partially eaten green lead on a tree — In this image of the spongy moth caterpillar, you can clearly see the rows of blue spots and then red. Photo by Jennifer Correa-Kruegel.

Explore any wooded area in north Jersey in early springtime and you’ll likely see the egg masses of the spongy moth (formally known as the Lymantria dispar dispar). The spongy moth, which is so called for the texture of its eggs, was rebranded with its new moniker nearly four years ago.

This moth is one of many different types of invasive species of either plants, animals, or insects—typically from another country or area—that outcompete native species for resources. The spongy moth population does most of its damage when they are in their larvae or caterpillar stage. In spring, thousands of these tiny caterpillars hatch from small beige fluffy clumps that remain on the sides of trees from last summer.

The Life Cycle of Lymantria Dispar Dispar

Once hatched, the tiny caterpillars move their way up the trunk of the tree to consume their food of choice, which is the leaves of any number of a variety of deciduous trees. As the caterpillars shed and grow larger, the more food they eat and the more destructive they become.

In fact, when observing particularly bad infestations, it may sound like it is raining—even on a beautiful clear day—because of the sound of their frass (caterpillar poop) raining down below them.

Spongy moths do not fly at this stage in their development. They instead travel from tree to tree by hanging from a thin webbing and letting the wind blow them to the next tree; in this way, they can systematically defoliate thousands of acres of forest.

Spongy moth eggs on the trunk of a deciduous tree. Photo by Jennifer Correa-Kruegel.

Once they have completed four to six molts, the spongy moth will pupate, or form a cocoon, eventually emerging as an adult moth. Once it reaches the adult stage, the spongy moth does not eat: This part of its’ life cycle is only for reproduction.

The male spongy moth will fly around in search of the pheromones of a female spongy moth, the females of the species being entirely flightless. After the pair have mated, the female will lay her eggs and die. Unless consumed or destroyed, her eggs will remain there until the next spring.

Lymantria Dispar Dispar Arrives in New Jersey

It is not often that biologists can pinpoint the specific dates when an invasive species is believed to have arrived, but in this particular case they have attributed the release of the moths to a person by the name of E. Leopold Trouvelot.

Trouvelot intentionally brought the caterpillars over from Europe thinking they could make a cheaper version of silk from the thin webs they produce in their larval stage. When the experiment did not manifest the desired results, the larvae were simply released in an area of Boston in 1869.

How to Treat a Lymantria Dispar Dispar Infestation

Some controls of the spongy moth caterpillar involve aerial spray programs of a bacteria called Bacillus thuringiensis or Bt. The spraying of Bt needs to be done at a very specific time in the caterpillars’ life cycle because they need to consume the bacteria in order for it to erode their stomach lining and eventually kill them.

Spongy moths with wilt disease. Photo by Jennifer Correa-Kruegel.

Biological controls consist of fungus, viruses, wasps, and deer mice.

Wilt disease is visible in the last picture where the caterpillars are shriveled in an inverted V hanging from the tree. Wet springs will help this particular virus and it is passed from caterpillar to caterpillar as they climb over each other up the trees.

Millions of acres of forest have been defoliated by this invasive species that can pose serious risks to trees if they are defoliated too many years in a row, so treating infestations is vital to maintaining the health of our ecosystem.

Jennifer Correa-Kruegel, Warren County Naturalist

Jennifer has a Masters in Parks and Resource Management from Slippery Rock University. She worked as a Park Naturalist for Hunterdon County Park System from 2003-2006 and then at the NJSOC full-time from 2006 - 2020, starting as the Program Coordinator and evolving to an Environmental Educator. Jen is a New Jersey native and has lived in Warren County with her family since 2004. She is excited to be offering programs to this community she has grown to love.