Close up of the bagworm's outer bag where pupal develop.


Adult females spend their entire lives serving as an egg-filled sac

Larvae can survive long periods without food

Weave twigs and leaves into their bags to blend into environment

Distributed widely in North, South, and Central America, the common bagworm is one of the most damaging pests of urban trees in the northeastern and southern U.S., including juniper, arborvitae, live oak, Southern red cedar, willow, maple, elm and pine. Throughout the U.S., the insect has one generation per year, overwintering in the egg stage inside the female’s pupal case.

All of the approximately 1,000 species in the bagworm (Psychidae) family have flightless adult females that spend their entire lives inside their pupal casings enclosed in an outer bag, in a caterpillar-like state, serving as an egg-filled sac. The male bagworms emerge as freely flying moths, hairy and charcoal black, with 25.4 mm long membranous wings. Neither the male nor the female adult feeds.

Hatching larvae are known to disperse to surrounding plants by spinning a silken thread and traveling on the wind, until finding a host tree, shrub or plant, where they begin feeding and incorporating materials such as pieces of twigs, leaves and silk into new bags of their own, helping them blend into the environment.

Throughout the seven larval instars, the caterpillar increases the size of its bag as it grows and can survive long periods without food, especially during the later stages of development. The fully-grown larva is approximately 25.4 mm long and takes up to four months to develop.