The bag is made from silk and is covered with bits and pieces of leaves and twigs from the host plant. The bag of a worm feeding on juniper will not look the same as the bag of a worm feeding on rose. The larva itself is dark brown with a yellow head and yellow and black spots on the body. 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.