bagworm, common name for the larva of small moths of the family Psychidae. The larva spins a silken cocoon as it travels, hence the term bagworm. When fully grown, the bagworm fastens its covering to a twig and pupates within it. Some species weave bits of leaves or twigs into their bags. During mating season the wingless, footless adult female perforates the lower end of the bag, protrudes her abdomen for breeding, and soon after laying about a thousand overwintering eggs in the bag, dies. The larvae develop slowly, requiring several months to reach maturity. Bagworms prefer arborvitae and juniper trees, but practically all trees are attacked. The best known of these small moths is Thyridopteryx ephemeraeformis, occurring throughout the E United States and regions adjacent to the Gulf of Mexico. Control of the pests is through use of insecticides or by handpicking the cocoons before the eggs hatch at the end of May. Bagworms are classified in the phylum Arthropoda, class Insecta, order Lepidoptera, family Psychidae.