Key points
- The common name of Gypsy moth has been officially changed to spongy moth.
- Spongy moth, native to Europe, was introduced and accidentally released in Massachusetts in 1869.
- Spongy moth (Lymantria dispar) is a serious pest of oak trees in Maryland and is considered a major forest pest. The first serious infestation in Maryland dates back to the 1980s.
- Predators, parasites, and diseases attack spongy moth caterpillars but the Maryland Department of Agriculture continues to survey for this pest to monitor populations. Areas with high populations are treated in cooperation with the USDA Forest Service, Maryland Department of Agriculture, local county governments, or landowners. For details search the Maryland Department of Agriculture website (https://mda.maryland.gov/).
- Spongy moth caterpillars feed in May and June. They prefer oak but will also feed on sweetgum, linden, willow, birch, apple, alder, boxelder, hawthorn, and blue spruce. A large population can defoliate acres of trees.
- Deciduous trees suffering more than 50% defoliation for two consecutive years will be significantly weakened and may die.
Spongy moth life cycle and damage
- Egg hatch begins in late April or early May depending on the temperature.
- Young caterpillars are black, hairy, and only one-sixteenth of an inch long. Very young caterpillars are carried by the wind from tree to tree.
- Spongy moths do not spin webs or make sacks in trees.
- As they grow they change color and by the third instar (development stage), the caterpillars are about five-eights of an inch long and have 10 blue spots down their backs.
- These young caterpillars spend most of their time in the treetops feeding. The damage looks like shot holes in the leaves and is not easily visible from the ground.
- Caterpillars grow up to 2 inches in length and then have 5 pairs of blue dots and 6 pairs of red dots (photo at top of page). The female can grow to about two and one-half inches. Large caterpillars can consume leaves to the midrib.
- The last stage caterpillars are responsible for most of the leaf loss in trees and are more difficult to control with pesticides than young caterpillars.
- When the caterpillars are finished feeding they migrate out of the trees in search of hiding places to pupate. The caterpillar changes into a smooth, teardrop-shaped, dark brown pupa that is about one inch long. They may be found attached to just about anything around the outside of the home including tree trunks, cars, trailers, around door frames, on the siding overhang above the foundation, and in many other protected locations.
- Adult moths emerge from late June to late July. Female moths have white wings with small dark markings (wingspan is two inches) and do not fly in Maryland.
- Male moths are brown with black markings and do fly. They are one of the few day-flying moths found in Maryland.
- Moths do not feed. The moths only live a short time during which they mate and the female deposits eggs in masses. Egg masses are felt-like, tan, oval, and about one and one-half inches long. They are laid in bark crevices, on the undersides of branches, on the ground under loose stones, boards, firewood, lawn furniture, campers, and many other places.
- There is one generation a year and winter is spent in the egg stage.