Large Numbers of Bagworms Found on All Sorts of Hosts

This insect is usually first detected by observing the larval bags made up of bits and pieces of host plant leaves and twigs that are woven together with silk. As the larvae grow and feed in the spring and summer, so do their bags. The bags can vary in length from ¼ to 2 inches. Many broadleaf and evergreen trees and shrubs can serve as hosts for bagworm species, including arborvitae and other ornamental conifers, cedar, cypress, elm, fruit and nut trees, juniper, oak, locust, maple, persimmon, pines, sycamore, willow and many other ornamental plants.
Although bagworm species vary slightly in habits and life cycle, the bagworm usually spends the winter months in the egg stage within the bag produced by the female from the previous fall. Very small larvae spin strands of silk and are carried by the wind onto other plants, or larger larvae can crawl to adjacent plants. Full grown caterpillars pupate within their bags usually in the late summer. The male moths emerge out of the bag. The male moths are black in color with ½ inch clear wings and feathery antennae. The male flies to mate with a female. The females remain inside their bags and do not have eyes, legs, mouthparts or antennae. After mating, the females produce between 500 to 1,000 eggs inside their bag and then die.
Infested plants develop more bagworms each year since the female stage does not fly. When there are large populations, the larvae can defoliate plants. Heavy infestations over several years, especially when added to other environmental stresses, can lead to plant death.

Some Control Options:

Non- Chemical Controls:
If only a few small trees or shrubs are infested, handpicking and destroying bags is recommended. During the winter months, the bags contain eggs and during the late spring and summer, the bags will contain a larva.


Chemical Control Options:
When many small bagworms, less than ½ inches are present, then it is recommended to treat with an insecticidal spray such as those containing acephate, azadiractin, spinosad, Bacillus thuringiensis var. kurstaki, permethrin, or bifenthrin.

Bagworm, Thyridopteryx ephemeraeformis (Haworth) (Lepidoptera: Psychidae), larval "bag" on arborvitae. Photo by Bart Drees, Professor and Extension Entomologist, Texas A&M University.