Western red-humped caterpillar

Western red-humped caterpillars are striking, with red-humped backs and yellow lateral stripes, feeding gregariously (in groups) on Prunus and fruit tree foliage in midsummer. They consume entire leaves except the midrib, potentially defoliating entire branches or young trees. This caterpillar is more common east of the Cascades but can appear in warmer areas of western Washington.

Prune and destroy branch tips with egg clusters and young caterpillars in early summer before populations expand. Hand-pick clusters of larger larvae and destroy them. Bt (Bacillus thuringiensis) sprayed on foliage when larvae are small provides excellent control with minimal non-target impact. Preserve parasitoid flies and wasps by avoiding broad-spectrum pesticides.