Pests

Webworms: Autumn’s Tree-Leaf Eater

by Daniel Frank, WVU Extension Service Entomology Specialist

Fall webworms-2 Signs of fall webworm (Hyphantria cunea) have been seen in some areas of West Virginia. Fall webworm larvae are a common defoliator of a number of ornamental and fruit trees throughout the state.

Newly hatched larvae form a web (tent) around themselves and their food, which increases in size as they develop and grow. Young larvae feed socially in a group, skeletonizing leaves. When older, they will consume entire leaves.

Fall webworm is often confused with the eastern tent caterpillar (Malacosoma americanum), which is quite different in both appearance and biology.

caterpillar-comparison

Fall webworms form loose silken webs around the ends of branches; the larvae feed on the foliage within the web. Conversely, the eastern tent caterpillar forms dense webs in the forks and crotches of trees; the larvae leave their web to feed, but congregate there at night and during inclement weather. In addition, fall webworm larvae occur in the summer and fall, but eastern tent caterpillar larvae occur in the spring.

Fall webworms-2 Since fall webworm feed on leaves late in the season and their webs are generally concentrated in limited areas, they do little real damage to well-established trees. However, the nests often look unsightly.

Control of fall webworm is often best achieved by pruning and destroying infested branches if the webs are within reach. The bacterial insecticide, Bacillus thuringiensis (Bt), and many synthetic insecticides are also effective against fall webworm. However, sprays are most effective if applied to the foliage closest to the web mass; spraying the web itself will not give good contact to the larvae inside.