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.
Males leave their bags, fly and search out bags containing females.
After mating, a female lays 500-1,000 eggs in her bag and dies. Because the larval stage is the only mobile stage, one bush can have a high population and another one several feet away can be free of bagworms. Several parasites feed on bagworms. Birds eat them and the worms can be killed by low winter temperatures. The bags and eggs can be destroyed or placed in deep containers that allow any parasites to escape while keeping the larvae in.