“Crush and Brush” Spongy Moth

Are you seeing these caterpillars on your trees or hiding underneath things left lying around the yard? They are spongy moth caterpillars (formerly known as gypsy moth) that are busy eating and getting bigger and bigger until they get ready to change into their adult moth form. The spongy moth has escalated into one of the most important insect pests of forest and shade trees in the eastern United States. They have moved steadily westward ever since their introduction in the late 1800s, reaching Wisconsin in the late 1980s.

Right now is the time to be “crushing and brushing.”

After feeding for several weeks, the caterpillars will look for a safe spot, then sheds their skin. Its new skin hardens into a dark brown shell and are called pupae. Spongy moths are immobile during their pupal stage and can be crushed or brushed into a container of soapy water to prevent them from making it to the adult stage. If caterpillars have been abundant in your area, do some thorough scouting to check for the brownish pupae (3/4 – 2 1/2 inches long), which are often tucked away in protected spots. If you are still seeing the caterpillars, crush those too.

Adult spongy moths appear within two weeks. Adult female spongy moths (pale colored) have limited mobility and can also be crushed or brushed into a container in soapy water. Since each female can easily lay upwards of 1,000 eggs, eliminating adult female moths could help prevent future problems!

For more information, check out the Wisconsin Spongy Moth Portal: https://gypsymoth.wi.gov/