Fall Webworm

Distribution and Hosts

Native to North America, the fall webworm occurs throughout the United States and southern Canada. Its hosts include more than 100 species of deciduous forest, shade, and fruit trees, with preferences varying from region to region.

Description of Damage

Newly emerged larvae immediately begin to spin a silken web over foliage on the terminal portions of the branches (Fig. 1). The larvae feed on the leaves within the webbing. As the larvae grow, webs enlarge and enclose more foliage. Large portions of tree branches are commonly enclosed by such webs and are most apparent from mid- to late-summer. Young larvae feed on the upper surfaces of the leaves while older larvae eat entire leaves except for the midrib and large veins. The insect is considered an ornamental pest due to the unsightliness of the webs, but it is usually not an important forest pest.

Identification

Eggs are small, yellow or light green, and usually deposited in hair-covered masses on the underside of leaves. Mature larvae are 25-31 mm (about 1-1.2 inches) long and covered with long silky hairs. The head color varies from red to black.

Caterpillar coloration is highly variable. Their color often ranges from white to pale yellow or light green (Fig. 2). There can be two lines of black dots down the back, sometimes with a black stripe down the center. There is usually a line of yellow spots along both sides along both sides. Sometimes larvae are partially or completely dark, but with light colored hairs.

Pupation occurs in thin cocoons usually spun in the duff or just beneath the surface of the soil below the host plant. The cocoons are usually covered with the larval hairs. The adult moth has a wingspan of 25-31 mm (about 1-1.2 inches) and is snowy white, usually with dark spots on the wings but sometimes pure white (Fig. 3).

Lepidoptera: Erebidae, Hyphantria cunea (Drury)

Life History

Adult moths lay their eggs from May to July. Eggs hatch within two weeks and the larvae immediately begin feeding and constructing webs. Larvae feed and continue to enlarge their webs for four to eight weeks. There are at least two generations per year in the South. 

Control

Nests can be cut out of small trees and destroyed. Insecticides may be applied against fall webworm from mid- to late- summer or when webs are first found. See the Virginia Pest Management Guide for Home Grounds and Animals (PMG 456- 018) or Horticulture and Forest Crops (PMG 456-017) for specific insecticide recommendations depending on homeowner or commercial production use. More than 50 species of insect parasitoids and 36 species of predators of the fall webworm are known in the U.S., but they are not commercially available. 

Revised

Theresa A. Dellinger, February 11, 2020.