Fall Webworm, Hyphantria cunea
 

Fig. 314   Adult fall webworm and larva.	Fig. 315  Fall webworm nests on walnut. Note enclosed foliage.	Fig. 316  Fall webworm larva.

Distribution:  Widespread throughout the Fraser Valley, also found in the the Okanagan and other interior locations. 

TREE SPECIES ATTACKED: Paper birch, black cottonwood, red alder and bigleaf maple are susceptible. The fall webworm also attacks willow and fruit trees.

WHAT TO LOOK FOR: Trees with nests that have foliage enclosed, and inside which are found gregarious, hairy caterpillars with a broad black dorsal stripe, and small black and orange knob-like, fleshy protuberances on either side.

INSECT DESCRIPTION & DAMAGE SYMPTOMS: Larvae are about 2.5 cm long when fully grown. They have pale yellowish bodies with a broad black dorsal stripe. They have small black knob-like fleshy protuberances on the dorsal stripe and orange ones on either side, from which long silky hairs arise in tufts. Adults have a nearly white body, white wings usually without markings, and a wingspan of 3.0 to 4.0 cm. Adults are found in June and July. Eggs are laid in masses of up to 300 on the underside of leaves, and are covered with white hairs from the female's abdomen. Young larvae web leaves together to construct a nest, and the gregarious larvae feed throughout the summer on foliage enclosed by the nests. The nests are enlarged as the larvae grow, and they may enclose several branches. Pupation takes place in cocoons woven in bark crevices, beneath stones, or in the litter or soil, where pupae overwinter. There is one generation per year.

DAMAGE: High populations do not usually persist for more than 2 or 3 years, and healthy trees are unlikely to be killed. This insect causes little permanent damage.

SIMILAR DAMAGE: Fall webworm larvae are found in nests that enclose foliage. Northern tent caterpillar tents occur on branches and stem, enclose less foliage than fall webworm nests, and the larvae are found on the surface of the tents.

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Contact Tim Ebata if you have comments on the presentation of this information.

BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136

Last updated March 04, 2002