By the time it is fully grown, to about one inch long, it will have five pairs of blue spots down its back, followed by six pairs of red spots. The first 3 larval instars stay in the branches of the crown of host trees. Larger fourth instar caterpillars move down the tree to rest during daylight hours, returning up the tree trunk to feed at night. Larvae reach full size by mid-June to early July. The pupa stage is spent in locations where the larvae hide, such as in bark crevices or on the ground.
Males emerge before females.
Males fly in a characteristic zigzag pattern. After mating, females lay eggs in July or August to complete the life cycle. It is important to distinguish gypsy moth caterpillars from other caterpillars that defoliate trees. The fall webworm will be smaller than most gypsy moth caterpillars. The cankerworm is hairless and pale to dark green and should readily be identifiable from gypsy moths.