Fall Webworm

The fall webworm is a native North American moth larva recognized for the large, loose silken webs it spins around the foliage at the ends of tree branches, a habit that distinguishes it from the similar-looking eastern tent caterpillar, which builds tighter tents in branch forks earlier in the season. Fall webworms feed on a very wide range of deciduous trees, including pecan, walnut, birch, cherry, and many others, making them one of the most widely distributed defoliating caterpillars in North America.

Though webbed branches can look unsightly, especially on ornamental and shade trees in late summer, the caterpillars generally feed on leaves that are already nearing the end of their seasonal usefulness to the tree, and healthy established trees typically tolerate the defoliation without lasting damage. The species has also become established in parts of Europe and Asia as an introduced insect.

• Pale yellowish-green to cream body covered in long, soft, whitish hairs
• Head can be either black or reddish-orange depending on the regional race
• Row of dark spots along the back, partially obscured by hair tufts
• Grows to about 3.5 cm at maturity
• Found feeding communally inside a loose, expanding silk web at the tips of branches
• Distinguished from eastern tent caterpillar by the messier, tip-of-branch web (rather than a tight tent in a branch fork) and later-season timing

Widespread across North America and introduced to parts of Europe and Asia, fall webworms are found on a broad range of deciduous host trees in forests, parks, orchards, and urban landscapes. Webs become most conspicuous in late summer and early fall as larvae grow and enlarge their communal shelter, in contrast to the spring-active tent caterpillars.

Fall webworm caterpillars feed communally within their expanding silk web, which encloses the leaves they are actively consuming and expands outward as they need more foliage, unlike tent caterpillars which venture outside their tent to feed. This webbing behavior protects the colony from many predators and weather, though it also makes their presence highly visible on host trees. As generalist folivores capable of feeding on dozens of tree species, they play a role in seasonal leaf turnover and serve as prey for parasitic wasps, predatory insects, and birds that are able to access the web.

Adult moths lay egg masses on the undersides of leaves in late spring to summer, and the emerging caterpillars immediately begin spinning a communal web around nearby foliage. Larvae feed and grow within the enlarging web for four to six weeks, passing through multiple instars, before leaving to pupate in a cocoon spun in leaf litter, bark crevices, or soil. Depending on climate, the species may produce one to four generations per year, with the final generation overwintering as pupae until moths emerge the following season.