Where it came from
Europe, North Africa, and temperate Asia.
How it got here
In 1869 an amateur entomologist named Étienne Léopold Trouvelot brought egg masses to his home in Medford, Massachusetts, hoping to breed a hardier silk moth. Some escaped from a window. Within 20 years they were defoliating the town, and they have been spreading west and south ever since.
What it does to the ecosystem
Caterpillars prefer oaks and strip entire forests bare during outbreaks, which recur every 8 to 12 years. Trees usually re-leaf but are weakened, and two or three consecutive years of defoliation kill them, especially in drought. Long Island's oak-dominated pine barrens are prime habitat.
What it costs
Tens of millions of acres defoliated over the last century, billions of dollars in timber loss and control, and neighborhoods where caterpillar frass falls like rain for weeks.
Don’t confuse it with
- Eastern tent caterpillar and forest tent caterpillar (native). Tent caterpillars have a solid white stripe or a row of white keyhole marks down the back; spongy moth caterpillars have five pairs of blue dots followed by six pairs of red dots and no tents.
How to identify it
Hairy caterpillars with five pairs of blue dots followed by six pairs of red dots along the back; tan fuzzy egg masses on bark and outdoor objects.
What to do
Scrape egg masses into soapy water in winter; use burlap bands on trunks in spring. Outbreaks usually collapse from disease within a few years.
On Long Island
Outbreaks hit the Central Pine Barrens and North Shore oaks periodically, most recently in the early 2020s. Scrape egg masses off trees and outdoor items in winter.
Worth knowing
- The name was changed from gypsy moth in 2022; spongy refers to the texture of the egg mass.
- A fungus (Entomophaga maimaiga) and a virus now usually collapse outbreaks within a few years.
- Females cannot fly; the species spreads when tiny caterpillars balloon on silk or when egg masses ride on cars and campers.
