Western Tent Caterpillar

    Western Tent Caterpillar

    Malacosoma californicum

    western tent caterpillar

    Western tent caterpillar egg mass and adult (Jerald E. Dewey, USDA Forest Service, Colorado State University, Bugwood.org)

    westerm tent caterpillar larva

    Western tent caterpillar larva (Whitney Cranshaw, Colorado State University, Bugwood.org)

    western tent caterpillar

    Tent made by western tent caterpillars (Robert Efram, Bugwood.org)


    Pest Description

    • adults: wingspan 1 – 2 inches; heavy bodied; dark red brown to yellow, tan or gray
    • larvae: ~ 2 inches; hairy; coloration can be highly variable
    • pupae: made of white silk with a white to yellow dusting
    • eggs: brown to gray, shiny; laid in masses on branches

    Host Plants, Diet & Damage

    • quaking aspen, alder, bitterbrush, California lilac, chokecherry, cottonwood, crabapple, fruit trees, mountain mahogany, nine-bark, oak, poplar, serviceberry, sumac, wild currant and wild rose
    • feed on leaves within unsightly, silken tents
    • larvae can defoliate leaves or trees
    • yearly defoliation can cause reduced growth or kill trees

    Biology, Life Cycle & Damaging Life Stage

    • overwinter as unhatched larvae within eggs on host trees
    • larvae hatch around budbreak in spring
    • larvae feed within silken tents; later larval stages may become solitary
    • pupation occurs 1 to 1 1/2 months after spring egg hatch
    • pupae are silken cocoons stuck to host trees, non-host trees or in leaf litter
    • adults fly late-July through August and lay egg masses
    • one generation per year in northern Utah
    • larvae are the damaging stage

    IPM Recommendations

    • Manage trees to improve or maintain overall health.
    • Monitor trees after budbreak for larvae and silken tents.
    • Severe damage to ornamental plants is uncommon; tolerate pest.
    • Apply an insecticide (Bacillus thuringiensis var. kurstaki; carbamate; organophosphate; pyrethroid; spinosyn) to foliage targeting small larvae.