The needles are chewed, and individual branches or the entire tree or shrub may be defoliated. Hanging from the branches are carrot-shaped cases, or ''bags'', 1-3 inches long. The bags are constructed from interwoven bits of dead foliage, twigs, and silk. When a bag is cut open, a tan or blackish caterpillar or a yellowish grublike insect may be found inside. A heavy attack by bagworms may stunt tree growth.
Apply an insecticide labeled for this pest, following label instructions. Handpicking and destroying bags from fall to spring will reduce the number of overwintering eggs.