Scientific Name: Lymantria dispar
Formerly known as: Gypsy Moth
Damages: Forests and Trees
- Eastern tent caterpillar
- Fall webworm moth
(Lymantria dispar asiatica)
Over one hundred years ago, spongy moth caterpillars were brought into the U.S. for research as a possible source for silk production. Escapees found a welcoming habitat, and masses of caterpillars have been plaguing our forests and landscapes on and off for over a century.
Life Cycle and Behavior
In July and August, females lay dark brown masses of 100 to 600 eggs protected by a light-colored, almost hairy covering. The older the mass, the softer they are to the touch. They are often on tree trunks, but can be found on the side of buildings, signs, trailers, are other outdoor surfaces.
The following spring, ¼ inch (6.3mm) long hatchling caterpillars move away from the egg mass to feed on leaves. To do so, they often produce silken threads that catch in the wind and send them aloft to other trees—a practice called ‘ballooning’ that enables their spread.
- Early instar larvae are small, dark brown-to-black, and very fuzzy.
- Later instars lighten in color and have a showy display of two rows of colored spots: five pairs of blue and six pairs of red.
- At about seven weeks, larvae are fully grown at 2 – 2 1/4 inches long (50-56 mm).
In June and early July, larvae pupate in hiding spots under bark or similar protection. The dark brown, hairy pupae are about 2 inches long.
Males—Once they complete pupation, adult male spongy moths emerge and fly erratically during the daytime in search of mates.
Females—Heavy-bodied adult females have wings but don’t fly. They rest on trees and wait as males follow female pheromone trails to find them.