Importance. - Bagworms are one of the most important pests of evergreen ornamentals in the South. Arbovitae and juniper are particularly susceptible. If infestations are heavy enough, they will strip evergreen shrubs of their foliage and cause branch dieback or death. Some hardwood species - such as maple, oak, dogwood, and willow - also are attacked, but rarely are they damaged as severely as conifers.
Identifying the Insect. - Bagworms are larvae and are rarely seen outside the bags they construct. The wingless female moth is grub-like and remains inside this tough, silken bag her entire life. Males are nimble fliers, and in the fall can be seen circling around infested trees in search of a mate.
Identifying the Injury. - Bagworms consume the entire needle or leaf, leaving only the needle sheath or mid-rib. They usually feed on one branch at a time. An indication of damage is the presence of bags suspended from twigs and branches.
Biology. - Bagworms overwinter as eggs, inside the bag that contained the female. In the spring, the eggs hatch and the larvae crawl out in search of food. By using silk and bits of needles, bar, or twigs, they construct a bag around themselves. When fully grown, the bags are between I 1/2to 2 1/2 inches (40 to 65 mm) in length and the larvae permanently suspend their bags from twigs and pupate. In the fall, the male moth emerges, flies to a female's bag, and mates. The female lays between 500 and 1,600 eggs within her bag. There is one generation annually.
Control. - In most cases, bagworm outbreaks are quickly reduced by low winter temperatures and a complex of several parasites. On ornamentals around the home, it is often practical to control bagworms by picking and destroying the bags. Chemical control is also effective.