Hosts: Willow, alder, ash, chokeberry, cottonwood
Larvae feed on foliage, forming large webs in the branches
of trees. Webs are noticeable in the fall when larval feeding takes
place. There are two races: a blackheaded or northern race and a
redheaded or southern race. Larvae of the southern race are yellowish-tan
with red or orange colored heads and brownish hair that arises from
reddish-brown tubercles. Larvae of the northern race have a black
head with a pale yellowish or greenish body that has a dark stripe
on the back, and long white hairs rising from red or black tubercles.
The black-headed race predominates in the West. Adults are white
in color with orange markings on the body and legs. The wings have
some black spots and a wing expanse of approximately 30 mm.
Fall webworm has one generation per year. Adults appear and
lay eggs in late June and early July. The eggs hatch and the small
larvae feed on both leaf surfaces while larger larvae will consume
the whole leaf. Larval feeding continues until mid-September. The
insect overwinters in the pupal stage in a transparent cocoon in
the soil, leaf litter, or on tree trunks.
Effects: This insect causes minor defoliation
in most forested situations. It can cause loss of visual quality
in ornamental plantings.
Similar Insects and Diseases: The western
tent caterpillar is sometimes confused with the fall webworm,
due to both having dark heads and dark stripes down their backs.
However, western tent caterpillars feed in the spring while fall
webworm feeds in the fall.