Egg-The yellow egg is slightly oblong or spherical, about 0.8 mm by 1.0 mm. It is found in the mother's bag, usually in her pupal exuviae.
Larva-The male is 2 to 43 mm long; the female, 2 to 52 mm. The head and forward parts are dark and sclerotized the remainder is pale amber. Larval bags grow to about 5 cm long and 12 mm wide (Color Plate 1G).
Pupa-The pupa is dark brown. Males are slender posteriorly, and females are cylindrical. The pupal stage is spent inside the bag.
Host Plants -Bagworms feed on many trees including maple, boxelder, sycamore, willow, black locust, elm, linden, poplar, oak, apple, wild cherry, sassafras, and persimmon; but the preferred hosts are conifers. Arborvitae is highly susceptible.
Damage -A single bagworm does relatively little damage. Yet because females do not fly, populations are often very dense; and excessive defoliation may actually kill conifers within one or two seasons. Damage is most noticeable on ornamental plantings rather than in forests and woodlands.
Life History -The bagworm is sometimes called the evergreen bagworm. Populations vary, but occasionally bagworms become extremely abundant, alarming homeowners. The winter is spent as eggs (500 to 1,000) in the mother's bag. They hatch in May and June, and the young worms drop from the bag on a slender silk thread. Such small worms may be "ballooned" for short distances on this long 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. Before the young worm feeds, it secretes silk and forms a bag. Bits of plant tissue become enmeshed in this bag when the worm feeds. As the worm grows, the bag enlarges, reaching about 5 cm when complete. It is fastened to the plant by silk manufactured whenever the worm rests or molts.
Where practical, bagworms can be removed with scissors or a sharp knife. Bagworms are parasitized by several ichneumonid and chalcid wasps. Low winter temperatures and bird predation on small larvae are also limiting factors. Chemical control is effective, particularly in June and early July when the bags are small. For specific chemical controls, see the current state extension service recommendations.
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