Caterpillars do not build a nest or web. As they mature, they often feed at night and move down the tree to take refuge in shady places during daylight hours. Feeding stops around late July, larvae pupate, adults emerge and lay eggs in August. Mature larvae are hairy and have five pairs of blue spots and six pairs of red spots down the middle of their backs. Adult females are flightless, about 2 inches across, and whitish.
Male moths are strong fliers, smaller, and dark brown with feather-like antennae.
One generation occurs per year. Fall webworm will feed on almost any deciduous tree, but prefers black walnut, hickory, cherry, and American elm. A larval colony will build a silken nest around foliage and begin feeding inside the nest. Larvae expand their nest to include new branches as they seek additional foliage on which to feed. Larvae are yellowish, hairy, and have either a black or red head.