Spongy moth is the common name of a moth that is destructive to forest, shade, and fruit trees. The moth caterpillars eat the leaves of both broadleaf and needleleaf trees. During large outbreaks, the caterpillars can completely strip a tree of its leaves. They are particularly destructive to oak trees.
About 1869, spongy moths from France were accidentally introduced into the forests of Massachusetts. Since then, these European moths have spread as far north as southern Canada, as far south as North Carolina, and westward into Ohio and Michigan. They have been found as far west as California and Oregon.
The caterpillars of European spongy moths hatch in spring. They are brown to black with hairlike tufts. Older caterpillars have five pairs of blue spots and six pairs of red spots on their backs. The caterpillars reach their full size of 11/2 to 21/2 inches (3.8 to 6.4 centimeters) by midsummer. They then enter the pupal stage. After 10 to 17 days in a hard, brown pupal shell, the insects emerge as adult moths. The brownish male moths are strong fliers. The much-larger, cream-white females cannot fly. The moths do not feed. After mating, the females lay amber-colored clusters of fewer than 100 to more than 1,000 eggs. The moths die soon after mating.
In 1991, spongy moths from Asia were mistakenly introduced into Oregon, Washington, and British Columbia. They also were brought into North Carolina in 1993. The Asian moths are similar in appearance to European moths. But unlike the female European spongy moth, the female Asian spongy moth can fly. It may lay eggs more than 20 miles (32 kilometers) from where it lived as a caterpillar.
Natural enemies of spongy moths include predatory and parasitic insects, disease-causing microbes, fungi, and insect-eating birds and mammals. To help control the moths in North America, scientists have introduced various predatory and parasitic insects from Europe and Asia. A fungus native to Japan has helped control the moth caterpillars in parts of the Northeast. This fungus, called Entomophaga maimaiga, feeds on the tissues of the caterpillar.
Spongy moths can be destroyed by coating the egg clusters with a pesticide or by collecting and sealing the eggs in cans. Caterpillars can be collected by banding tree trunks with coarse cloth or with a sticky substance called tanglefoot. Spraying trees with insecticides in the spring kills the moths, but it can harm the environment. Spongy moths can also be killed by spraying trees with Bacillus thuringiensis, which is a naturally occurring bacterium.
Until 2022, the spongy moth was commonly known as the gypsy moth. However, that name is considered offensive and is no longer used by most entomologists (experts on insects). See Roma.
