Fall webworm

Natural History
Webbing from fall webworm
Photo credit: G. K. Douce - University of Georgia

The fall webworm (Hyphantria cunea) feeds on many hardwood trees throughout the United States but is not considered a major pest in most areas. The web or tents that the caterpillars build in trees is considered unattractive by many people. In Florida, the fall webworm is common and can cause serious damage to commercial pecan groves.

In the spring, the female webworm moths lay egg masses with 400 to 500 eggs on the underside of leaves in the host tree. The female covers the egg mass with white hairs. After one to two weeks, the larvae hatch and immediately start to eat surrounding leaves and begin to build their web-like nests in the trees.

For four to eight weeks, the larvae continue to devour leaves and expand their webs. Eventually, the larvae spin a cocoon, usually on the ground near the tree, where they stay throughout the winter. This cycle can be repeated several times in one growing season. The following spring the moths emerge and mate to start the cycle over again.


Identifying Characteristics

Identifying the injury: The major evidence of attack is the large silken web built by the larvae. These webs are located at the end of branches. The leaves within the webs will have been eaten by the caterpillars and will have a skeletonized appearance.
Identifying the insect: The adult fall webworm is a nocturnal moth. The wings are bright white (usually with dark spots) and the wingspan is 3 to 4 cm. The body is hairy and the bases of the front legs are orange or bright yellow.


The size in the larval "webworm" stage is variable, but the caterpillars are approximately 35 mm long when mature. Depending on the variety, the head can be black or deep orange to red. The body color can be yellow, green, gray, brown, or black, usually with a black stripe on the back and a yellow stripe on each side. The body is covered with long white or brown silky hairs. Many caterpillars can be found living together in the tent.
Susceptible trees: Fall webworm can feed on many species of hardwood trees, but in Florida this insect seems to prefer persimmons, hickories, sweetgums, and pecans.



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