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. 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. Caterpillars favor oak but will feed on the foliage of many tree species, including some conifers.