Identification & Life Cycle

The gypsy moth, Lymantria dispar (L.), gets its name from a behavior of its larger caterpillars, which generally migrate each day from the leaves and down the branches and trunk to rest in shaded spots on the tree or objects on the ground. Caterpillars are dark and have dark hairs, but they are not so hairy that one cannot see the five pairs of dark blue spots and six pairs of brick red spots along the back. Most caterpillars attain full-size in early summer and transform to the pupil stage. The pupae stage lasts about ten days to two weeks. Adults emerge in late June or in July. Females' wings are white with black lines, but they are too heavy to fly. Male moths are mostly brown and do fly. Females lay 300-1,000 eggs in a single group, mingled with light brown hairs from the female's abdomen. Adults soon die, but the eggs survive over winter. Caterpillars hatch the next spring. Caterpillars favor oak but will feed on the foliage of many tree species, including some conifers. Defoliation by caterpillars of gypsy moth weakens trees, because without leaves the trees are not able to manufacture food. Weakened trees are susceptible to bark beetles and root diseases that can kill them. It is fairly easy to identify gypsy moth because colors of caterpillars, adults, and egg masses are so distinct. Also, egg masses are large compared to those laid by most insects. Therefore, it is possible to predict defoliation for the following spring and prepare a suppression program to reduce the numbers of caterpillars.