- adults: wingspan is 1 1⁄2 inches long; pure white, sometimes with brown or black spots
- larvae: ~ 1 inch long; hairy, sometimes with distinct, paired black spots on back
- larvae: two color forms: redheaded race is dark with reddish hairs;
- blackheaded race is pale yellow to green with light-colored hairs
- larvae form silken tents around feeding area
- pupae: light brown, hairy masses
- eggs: small, round and laid in masses on leaf undersides
Host Plants, Diet & Damage
- over 100 host species; cottonwood, chokecherry, mountain-ash, elm and willow are preferred
- eed on leaves within unsightly, silken tents
- young larvae feed in groups, finely skeletonizing leaves
- older larvae can defoliate trees
- can stress or kill trees via multiple years of defoliation
Biology, Life Cycle & Damaging Life Stage
- overwinter as pupae near or on host trees
- adults emerge in June and July and mate
- deposited eggs hatch in 1 to 2 weeks
- larvae feed on foliage for about 6 weeks before pupating
- one generation per year in northern Utah
- larvae are the damaging stage
- Manage trees to maintain overall health.
- Monitor in late-June to early-July for egg masses or larvae.
- Minor feeding from small populations can be tolerated.
- Apply an insecticide (Bacillus thuringiensis var. kurstaki; carbamate; pyrethroid) to foliage targeting larvae when they are small.
For more information, see our Fall Webworm fact sheet.