Fall Webworm; Hyphantria cunea (Drury)
Extension Tips
By: Robert N. Brewer, Jr.

This is an example of web worms seen in a wooded backyard in Hiawassee.

The fall webworm is a native of North America and Mexico. Depending upon location, there can be from one to four generations per year. Webworms enclose leaves and small branches in their light gray, silken webs. The fall webworm is usually of only minor economic importance as a forest pest. However, shade trees and ornamentals can be heavily defoliated and the presence of the large, unsightly webs can make them aesthetically detracting. Persistent infestations of individual trees may cause limb and branch dieback and may reduce nut production on pecans.

Hosts: The fall webworm is known to feed on more than 100 species of forest and shade trees. In the eastern U.S., pecan, walnut, American elm, hickory, fruit trees, and some maples are preferred hosts; in some areas persimmon and sweetgum are also readily attacked. In the west, alder, willow, cottonwood and fruit trees are commonly attacked.

Evidence: Adult moths have a wingspan of between 1.4-1.7 inches (35-42mm). The bases of the front legs are orange or bright yellow. In the southern part of its range, the moth is white with dark wing spots while in the Northern parts of its range it is nearly always pure white and was once thought to be a separate species. Adults appear mostly from May to August and deposit their eggs in hair-covered masses of several hundred each, usually on the underside of host leaves.

Larvae are usually pale yellowish-greenish, with a broad, dusky strip down the back and a yellowish stripe down each side. Full grown larvae may reach a length of 1 inch or more (25mm). Larvae are covered with long, silky gray hairs arising in tufts from orange-yellow or black tubercles: head color varies from red to black. Newly hatched larvae immediately spin a silken web over the foliage on which they feed. As larvae grow, they enlarge the web to enclose more foliage. On heavily infested trees, several branches may be enclosed in webs.

Occasionally, small trees may be completely encased in webbing. Larvae are gregarious until the last instant when they leave the web and feed individually. Pupation occurs in thin cocoons usually spun in the duff or just beneath the soil.

Damage: Though the webs are unsightly, damage to most trees is considered to be insignificant. However, in areas where multiple generations attack and heavily defoliate trees, including in pecan production areas, control measures may be needed. Contact your local Extension office for appropriate control strategies if needed.