Summer is Peak Time for Bagworm Reproduction

First posted on 07-31-2009

By Elizabeth Fortune, Extension Communications Specialist

Summer is the time when a common Arkansas pest, the bagworm, works to become more common, said Mark Keaton, Baxter County extension agent for the University of Arkansas Division of Agriculture.

“Bagworm pupation occurs in late summer and within seven to 10 days, the adult emerges,” he said. “Males are free-flying and leave their bag and search out bags containing females.

After mating, the female lays 500-1,000 eggs in the bag, drops to the ground and dies.”

The eggs overwinter in the bags. The bagworms create only one generation each summer.

The bagworm is native to the United States and their spindle-shaped bags of silk, covered with bits of needles or leaves white, are commonly seen in trees in Arkansas.

“They can cause severe damage to many species of trees and shrubs,” Keaton said. “They are rarely a serious problem on deciduous trees, except as a source of infestations that may move to evergreens. By knowing more about bagworms and being on the alert for them, you can avoid severe damage.”

In urban areas, juniper, arborvitaes, pine and spruce may be killed if bagworms completely defoliate them. Less severe attacks will retard growth.

“They’ll also feed on shade, orchard and forest trees of nearly every kind, as well as many ornamental shrubs and perennial plants,” Keaton said.

“Damage is caused by the larvae, or caterpillars, inside the bags,” he said. “The larvae eat the needles or leaves, and a heavy infestation can completely strip a plant of its foliage. Complete defoliation can result in the death of the plant.”

A very effective control method is picking the bags off the host in the winter or early spring.

“Since they contain many eggs, it is quite easy to prevent problems in the coming year,” he said. “These bags should be burned to destroy the eggs.”

Chemical control is most effective in spring and early summer before the bagworms become half-grown or larger. Large worms are very hard to kill. Thorough coverage of infested plants with insecticide is necessary for effective control.

Some of the insecticides that are labeled for bagworm control are acephate, Sevin, malathion, bifenthrin, Bt, spinosad, fluvalinate, and cyfluthrin. Be sure to always read and follow the label directions.

For more information about controlling pests, visit http://www.uaex.edu, or contact your county extension office.