Arborvitae Bagworms: Identification, Life Cycle, and Control

Four-year-old arborvitae show distress; two dead with "cocoon-like" bags containing large worms.

Pest: Bagworms (Thyridopteryx ephemeraeformis)

• Caterpillars build spindle-shaped silk bags camouflaged with foliage.
• One generation/year; overwinter as eggs in female bags (300–1000 eggs).
• Hatch late May–June; larvae balloon on silk to new hosts.
• Feed through summer; pupate August; males emerge, mate, females lay eggs.

Control

• Hand-pick bags in fall/winter; cut attachment silk to prevent girdling.
• Insecticides (acephate, bifenthrin, carbaryl, Bt) applied late June when larvae young and bags small.
• Thorough foliage coverage essential.

Trees usually refoliate after feeding stops.