Pupa -The pupa is dark brown. Males are slender posteriorly, and females are cylindrical. The pupal stage is spent inside the bag. Arborvitae is highly susceptible. Damage -A single bagworm does relatively little damage.
Damage is most noticeable on ornamental plantings rather than in forests and woodlands.
Populations vary, but occasionally bagworms become extremely abundant, alarming homeowners. They hatch in May and June, and the young worms drop from the bag on a slender silk thread. In August, the worms mature and change into the pupal stage. During August and September, male moths emerge from their bags to mate, living 1 or 2 days. Female bagworms, living 4 to 9 days, do not leave the bag until the eggs are laid.