Strange Webs in Trees: The Work of Fall Webworms

Fall Webworms appearing in trees throughout the area.

   The Extension office has received numerous calls from homeowners concerned about strange webs that have appeared in some of the trees in their home landscapes. A common misconception is that they are the result of some spider. The cause is an insect called the fall webworm. They appear in late summer and early fall and attack a multitude of plants, including many fruits, nut and ornamental trees and shrubs. In some cases the webs are so numerous they can cause the tree branches to break. Infestations are unsightly but rarely harmful to the trees.

    The fall webworm is a caterpillar; the larval stage of a small white moth. Full-grown caterpillars are approximately 1-inch long, pale green or yellow, and covered with tufts of long, white and black hairs. The insects often cover entire branches with their webs. The larvae feed within the web, eating leaf tissue between the leaf veins. The larvae drop off the tree and enclose themselves in cocoons. They spend the winter as pupae in silken cocoons on the ground or the bark of the tree. In the spring, the moths emerge from their cocoons, disperse and mate. Female moths deposit their eggs on the undersides of the leaves of plants they like to eat. The webworm eggs hatch later in the season, and the larvae begin to build the web. As the larvae consume leaves within the web, they expand the web to take in more and more foliage.

     Often the insect is confused with the Eastern tent caterpillar, which spins webs during the spring in the crotches of the trees. Fall webworms make their webs in the outer limbs of the trees in the autumn.

Eastern tent caterpillars build their nest in the crotches of trees.
They are active in the early spring

      The caterpillars can be controlled without insecticides. You can destroy the webs by using a long pole with a hook on the end and pull the webs down. Larvae can also be knocked out of lower branches with a stick or broom, or simple pruned. Many beneficial insects attack the egg and larval stages of fall webworm. You can help these predators and parasites get to their fall webworm prey by tearing open the webs.

      If webs are too numerous or too high in a tree to reach, sometimes insecticides, such as Sevin, can be used to kill the insects. Hose-end sprayers or commercial high-pressure sprayers are best for reaching upper portions of tall trees. Use caution when applying insecticides above your head and wear all the proper protective clothing required on the chemical label, insecticide sprays must penetrate the web deeply to be effective since the webbing is quite tough and difficult for the spray to get in. Please make sure you follow all label directions and safety precautions when applying pesticides.

    The webs caused by the fall webworms seldom harm the trees. Often just ignoring them and leaving them in the trees is the best course of action to take.