Tent caterpillar

Tent caterpillars construct large silken webs over foliage in spring, with larvae feeding on leaves inside and around the web. Look for grayish tents in branch crotches of alders, willows, and fruit trees by April in western Washington. The caterpillars are dark with light-colored stripes and yellow heads. Complete defoliation of small trees is possible, though mature trees recover.

Prune out tents with larvae intact in late April or early May, and destroy them to prevent larval emergence. Since mature trees recover readily after one season of defoliation, this is cosmetic damage. Do not apply pesticides, which eliminate natural parasites that suppress populations the following year. Trichogramma wasps and Tachinid flies parasitize egg masses and larvae.