Spongy Moth Caterpillar

The Spongy Moth caterpillar, previously known as the Gypsy Moth caterpillar, may be munching in the leaves of your favorite tree right not.

JANESVILLE—You might have noticed black, hairy looking caterpillars eating the leaves of your oak, maple, birch and other trees and shrubs.

These caterpillars have been steadily eating and growing, turning into larger caterpillars with long hairs and distinctive red and blue dots on their backs. They are going to keep eating until July when they will spin a cocoon and pupate, emerging as adult spongy moths. Each year, spongy moth (Lymantria dispar) caterpillars eat the leaves of thousands of acres of hardwood forests, yard trees and other urban trees throughout the northeastern United States. Here are some common questions and answers about spongy moths and what you can do about them, offered by the UW Extension of Rock County.

- Spongy moth? Is this a new pest?

No, the name spongy moth replaced the previous name of this insect, gypsy moth, earlier in 2022.

- Why haven’t I seen them before?

Spongy moths have been present in southern Wisconsin for years, but have gone mostly unnoticed. Last year’s drought conditions allowed their populations to explode so many residents are noticing them for the first time or in much higher numbers than ever before.

- I have many trees on my property, should I be worried?

The caterpillars are voracious feeders and can defoliate trees, however, healthy trees and shrubs are likely to survive. The caterpillars are a nuisance and you can work to help reduce their numbers.

- What should I do?

Not all caterpillars are bad. Make sure you properly identify any insect or caterpillar that might be causing damage before practicing any management strategy. Visit the spongy moth information page to learn about what spongy moths look like, their life cycle and management options throughout the year. Right now, you can be reducing the number of spongy moth caterpillars by working to remove them by crushing them or putting in a bucket of soapy water, and you can try putting up burlap collection bands to collect the caterpillars and remove them. Throughout the rest of the year, you can be carefully removing and destroying the egg masses. These options can be found on the following website: https://go.wisc.edu/kz1yc1.

If you have questions about spongy moths or other gardening questions, please contact Julie Hill, Horticulture Outreach Specialist for UW-Madison Division of Extension Rock County by email julie.hill@wisc.edu or by calling 262-741-4958.