The fall webworm, a common native caterpillar, can be found throughout the United States and has caught my eye in several areas of Columbia County recently.
As the name implies, it’s a web-maker. The larvae feed in colonies on foliage of hardwood trees and spin grayish silk webs around leaves in the process.
Typically, webs are located at the outer ends of branches. However, when webworm populations are high, webbing is more extensive and might cover the entire crown of the tree.
Webworms are capable of defoliating and causing damage to forest trees, but it is more a pest of shade and ornamental trees.
The fall webworm has one of the widest host ranges of any caterpillar. In the Southeastern region, they infest pecan, walnut, elm and many other trees. Pecan trees are infested more frequently than others.
Fall webworms can have up to four generations in a year, with most of the activity occurring in late summer and early fall. The larvae or caterpillars are hairy, with distinct paired dark spots on each segment of the back.
They can vary in color, but the primary color for this area is a light yellow to pale green with white hairs. The mature caterpillar, about one inch long, will twitch and jump when disturbed to deter predators. The caterpillars transform into a white moth with a wingspan of 1½ inches.
The fall webworm will winter as a pupa in a flimsy, light-colored cocoon. These cocoons can be found in protected areas such as bark furrows, crevices along the sides of buildings and under leaves and trash on the ground. The adult moths emerge in June to July and begin laying eggs on the underside of leaves. Females lay their eggs in groups of 300 to more than 1,000 on foliage of host trees.
When the eggs hatch, the young larvae feed together. They will skeletonize the leaf and start forming the tent-like web. The young larvae do all of their feeding inside the tent. When full-grown, the caterpillars leave the tent to find a protected area for the winter.
Controlling fall webworms is fairly easy. The best way is to remove the web from the tree as they form. Simply use a pole pruner to reach them and remove the portion of the limb that has the web.
Since fall webworms don’t feed outside of the web, this will remove all of the caterpillars. There are insecticides that you can use, but they can be hard to apply, since most of the webs are located in the tops of trees.
Typically, fall webworms are only considered unsightly and do not typically cause major damage to the trees they infest. However, in some circumstances, the host trees can be completely defoliated. Healthy hardwoods usually survive and recover without permanent injury. Several consecutive defoliations, however, can cause dieback in the crown and may contribute to the death of these trees.