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 pupal 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. 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.