FLORIDA — Fall webworms, Hyphantria cunea (Drury), are normally observed during late summer and fall when people notice the unsightly whitish or light gray webs in certain trees.
Webworms enclose leaves and ends of branches with silken webbing. The worms (caterpillars) are found in this protective webbing consuming leaves. Although they can defoliate branches on which they feed, very little to no permanent damage is done. It’s more of an aesthetic problem.
The exception is when they repeatedly feed on economically important crops such as commercial pecan or mulberry production, where control measures may be justified. However, in most landscape trees, long-term damage is usually minimal.
The adult is a moth. They overwinter as pupae in soil or leaf litter.
This native insect of North America is known to feed on over 85 tree species. But in the Southeastern United States, they are more commonly found on pecan, hickory, common persimmon, sweet gum, black walnut, and bald cypress.
What they are eating (tree leaves) is a temporary part of the plant. Leaves on host trees emerge in spring, grow through summer and then fall away in mid-fall or early winter. These caterpillars are not feeding on or damaging a permanent part of the plant.
Webworms feed on trees in nature, along roadsides, in wooded areas, and in pecan orchards and landscapes. If you tagged or labeled some of the infested trees and then visited these same trees in spring, you’d find new leaves with no damage.
Some people overreact and prune out infested limbs. Left alone, these limbs would still be a part of the tree, eventually producing new leaves. Some people attempt to burn the webbing with caterpillars inside, possibly damaging healthy branches, twigs, and buds from the heat of the fire.
These “control” efforts can do more damage to the tree than webworms could ever do.
Natural predators and parasites help control webworms, including birds, predatory stinkbugs, and parasitic wasps. Insecticides may negatively interfere with these predators and parasites. Plus, it can be difficult and dangerous to apply insecticide overhead. And, the webbing is difficult to penetrate with water or sprays.
In most cases, it’s best to let these caterpillars run their course. Besides, they rarely cause lasting damage to landscape trees.
Here is a link to a UF/IFAS Extension publication with more information: https://edis.ifas.ufl.edu/publication/IN878