Fall Webworm Moth caterpillar (Hyphantria cunea)

3 August

A moth in the family Erebidae known principally for its larval stage, which creates the characteristic webbed nests on the tree limbs of a wide variety of hardwoods in the late summer and fall. It is considered a pest but although unsightly, does not harm otherwise healthy trees.

The caterpillars are highly variable in coloration, ranging from a pale yellow to dark grey, with yellow spots and long and short bristles. There are two cream stripes along the sides. The two races—one more common in the north, the other in the south—differ in head capsule coloration The maximum length of larvae is 35 mm. Webs are progressively enlarged and much messier looking than those of tent caterpillars (which occur only in spring and have shorter hairs and very little yellow on their bodies); also, webs from the fall webworm are concentrated to the tips of the branches, whereas the tent caterpillar webs are largely found in the unions. Larvae feed inside the tents until the late instars. Very young larvae feed only on the upper surfaces of leaves; later, they consume whole leaves. The larval stage lasts about four to six weeks. Larvae are known to wiggle vigorously at periodic intervals in synchrony. How they synchronize these movements especially when distributed over a wide area has not been established.