Common Name: Bagworm
Scientific Name: Psychidae: Thyridopteryx ephemeraeformis
Status: common pest of evergreens and shrubs
Damaging Stage: caterpillar

Biology: Adult male moths are black with clear wings but are very seldom seen or collected. The wingless adult female does not leave the bag after pupation, so is also not commonly seen. The small football shaped bags are the most noticeable form of the insect and are commonly found hanging from leaves and twigs.

Bagworm eggs hatch in mid-summer and the larvae crawl out of the bottom of the bag. There may be as many as 300 eggs per bag. Larvae are light brown or tan although some may have a mottled appearance. The small caterpillars spin silken strands that are either caught by the wind and dispersed or are wrapped around tree branches. From there they begin creating the small silk shelters, woven together with bits of foliage (bags) from their environment. Bagworms live within these bags for protection, and enlarge them as they grow. They may grow to 2 inches or more in length.

Injury: Bagworms prefer juniper, arborvitae, spruce, pine, and cedar but also may attack deciduous trees. They can cause severe damage to trees and shrubs as they defoliate the branches.

Action Threshold: Control should be considered if more than 20 bagworms are found on each frond or if plants are especially valuable or susceptible to injury.

Management: Bagworms can be physically picked off of tree branches in the case of a light infestation. When bagworm populations are above the action threshold, both biological and chemical control options are effective. Treating when the bagworms are very young (early June) is most effective.