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Bagworm Order Lepidoptera
Excerpted from Bagworms, by Philip J. Hamman, Extension Entomologist, The Texas A&M University System. L-1802.
The small, silk weaving that resembles a Christmas tree ornament on your favorite arborvitae is no there for decoration. Such woven bags protect the larvae and eggs of bagworms. Both broadleaf and coniferous trees and shrubs are attacked by this pest. Bag worms become exceedingly abundant every few years, but always present a persistent problem. Texas has several recorded species of bagworms… Infestations are not noticeable at first, but if left unchecked, can completely defoliate trees and shrubs. Control measures using insecticides must be timely to eliminate bagworm larvae.
Description:
Bag worms build a tough, portable silken case to live in. These bags are the most easily seen and identifiable feature of the insect. Outside, the silken texture of the bag is somewhat concealed and strengthened by layers of leaves, twigs and fragments of bark arranged in a crosswise or shingle fashion. The bag has a small opening at the narrow, lower end through which the worm expels refuse. A wider opening at the top allows the worm to partially crawl out to feed and make repairs or enlarge its bag.
Newly hatched larvae are about 1/25 of an inch long. At maturity they may be 3/4 to 1 inch in length. The adult female looks like a maggot, with no functional eyes, legs or antennae. Its body is soft yellowish-white and almost naked. The adult male, however, resembles a small moth. It has clear wings with a span of about 1 inch. It also has feathery antennae and is sooty black in color.
Biology
The adult female deposits large numbers of eggs in her bag and then wiggles throughout the lower opening, drops to the ground and dies. As the larvae hatch, they let themselves down on single strands of silk thread and attach to adjacent limbs or plants, where they begin building their own silk bags.
At intervals in its larval life, the bagworm closes the upper opening of the bag. This is done before each of the four or more larval molts and before winter hibernation or final preparation for pupation.
After larval development and a subsequent pupal period, adults emerge. The males escape through the lower end of their bags. The wingless females only emerge halfway and await mating with the males.
Control
Handpicking the pest is the surest and cheapest means of control for small evergreen shrubs and trees in home plantings. It is useful at any time during the year. Be persistent and be sure to pick all of the bags and then to smash or burn them. If thrown on the ground, the eggs in the bags will still hatch in the spring and larvae may crawl back into the trees.
When there are too many bags to handpick or the trees and shrubs are too large to reach safely, then the infested plants can be sprayed. Apply insecticide soon after bagworm eggs have hatched or while the larvae are small and actively feeding. Control is difficult and not as effective as the larvae mature and close their bags. Most treatments are effective in April, May and June. Contact the Walker County Extension Office for a recommendation to fit your situation.
The Walker County Extension Office may be contacted at
(409) 435 - 2426.
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