Two species of tent caterpillar are common in Washington. The forest tent caterpillar is about 2" long at maturity and has a bluish body with black and white markings. This species makes silk mats on branches and trunks. The western tent caterpillar is the most common species in western Washington. It is dark with orange and black markings. Characteristic tents are made on the tips of branches. Young caterpillars typically feed in large groups in the protection of the nests. Older caterpillars feed in small groups or as individuals. Tent caterpillars are present in spring and early summer. They can partially or completely defoliate trees, causing some loss of vigor. Badly weakened trees may be killed, but damage is rarely this severe.

Management Options

Non-Chemical Management

Strip or prune out and destroy nests and caterpillars as soon as noticed. This is best done in early morning or evening, when caterpillars are gathered in the nests.
Pick out and destroy the foamy-looking, grayish, 1/2" egg cases during the winter. These may be found in bands around twigs or in flattened masses on trunks.
Several natural parasites and predators help control tent caterpillar populations. Avoid use of broad-spectrum insecticides which kill beneficial insects.

Select non-chemical management options as your first choice!

Chemical Management

IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides

Apply in spring when caterpillars are small and have begun feeding. If Bt is chosen, be sure to apply when insect is feeding. Best time is when caterpillars are young. Use a spreader-sticker with liquid Bt formulations. Homeowners should not make foliar applications to trees over 10 ft tall. Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.

Listed below are examples of pesticides that are legal in Washington. Always read and follow all label directions.

Azamax Botanical Insecticide, Miticide, & Nematicide [Organic]
Active ingredient: azadirachtin | EPA reg no: 71908-1-81268
Bonide Thuricide BT Conc
Active ingredient: Bacillus thuringiensis subsp. kurstaki | EPA reg no: 4-226
Bug Buster-O [Organic]
Active ingredient: pyrethrins | EPA reg no: 1021-1771-54705
This list may not include all products registered for this use.

Images

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Caption: Tent caterpillars and webbing Photo by: R.S. Byther
Caption: Tent caterpillar egg mass Photo by: A.L. Antonelli

WSU Extension

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