Adult females are wingless and lack functional legs, eyes and antennae. They are almost maggot-like, yellowish and seldom seen. Adult males are typical moths, sooty black and densely hairy. Wings are nearly clear with a span of about an inch. The problem with bagworms is that they damage plants by defoliating them.
Heavy populations kill many an ornamental arborvitae and juniper.
The larvae hatch from overwintering eggs during May. Each spins a silken case that it carries about while it feeds. As it grows, the larva enlarges the bag and keeps adding bits of foliage as camouflage. To rest, a larva attaches its bag to a twig with silk. The insect pupates in late summer, emerging within 7-10 days as an adult.