Forest tent caterpillar (Malacosoma disstria)
Western tent caterpillar (Malacosoma californicum pluviale)
Pest description and damage The western tent caterpillar attacks a wide variety of plants including alder, apple, ash, birch, cherry, cottonwood, and willow, as well as fruit trees and roses. The adult moths are stout, light to darker brown, and are active in early- to mid-summer. Adults are attracted to lights at night. Western tent caterpillars are hairy, dull yellow-brown, with rows of blue and orange spots on the body. Forest tent caterpillars are black and blue with dorsal white footprints. Eggs of these moths are laid on twigs or buildings in masses and may be especially numerous around lights. The eggs are brown to gray in color, about 0.0625 inch long, and look like bits of gray, hardened foam. The larvae feed in large groups on foliage of host plants. Leaf defoliation can do significant damage especially to young, weak plants. Larvae of western tent caterpillars build modest silken tents over leaves at the tips of branches. The larvae leave the tent to feed in new areas but return in the evening. Both species can defoliate small trees and reduce growth, tree vigor, and make the plants more susceptible to competition, diseases or other pests. Healthy plants usually will grow new leaves by midsummer.
For biology, life history, monitoring and management
See Table 2 in: