The fall webworm, Hyphantria cunea, builds impressive silk tents that sometimes enclose entire branches. The tents appear in late summer or fall - hence the name fall webworm. It's a common pest of hardwood trees in its native North America. The fall webworm also presents a problem in Asia and Europe, where it was introduced.
The fall webworm is often confused with eastern tent caterpillars, and sometimes with gypsy moths. Unlike eastern tent caterpillars, the fall webworm feeds within its tent, which encloses foliage at the end of branches. Defoliation by fall webworm caterpillars does not usually cause damage to the tree, since they feed in late summer or fall, just before leaf drop. Control of fall webworm is usually for aesthetic benefit.
The hairy caterpillars vary in color, and come in two forms: red-headed and black-headed. They tend to be pale yellow or green in color, though some may be darker. Each segment of the caterpillar's body has a pair of spots on the back. At maturity, the larvae may reach one inch in length.
The adult fall webworm moth is bright white, with a hairy body. Like most moths, the fall webworm is nocturnal and attracted to light.
Fall webworm caterpillars will feed on any one of over 100 tree and shrub species. Preferred host plants include hickory, pecan, walnut, elm, alder, willow, mulberry, oak, sweetgum, and poplar.
The number of generations per year depends greatly on latitude. Southern populations may complete four generations in one year, while in the north the fall webworm completes only one life cycle. Like other moths, the fall webworm undergoes complete metamorphosis, with four stages:
Egg – The female moth deposits several hundred eggs on the undersides of leaves in spring. She covers the mass of eggs with hairs from her abdomen.
Larva – In one to two weeks, the larvae hatch and immediately begin spinning their silken tent. Caterpillars feed for up to two months, molting as many as eleven times.
Pupa – Once larvae reach their final instar, they leave the web to pupate in leaf litter or bark crevices. Fall webworm overwinters in the pupal stage.
Adult – Adults emerge as early as March in the south, but don't fly until late spring or early summer in northern areas.
Special Adaptations and Defenses:
Fall webworm caterpillars develop and feed within the shelter of their tent. When disturbed, they may convulse to dissuade possible predators.
The fall webworm lives in areas where host trees occur, namely hardwood forests and landscapes.
The fall webworm lives throughout the U.S., northern Mexico, and southern Canada – its native range. Since its accidental introduction into Yugoslavia in the 1940's, Hyphantria cunea has invaded most of Europe, too. The fall webworm also inhabits parts of China and North Korea, again due to accidental introduction.
Other Common Names
Fall Webworm Moth