chewed leaf Western Tent Caterpillar Update


Biology and Life History

The western tent caterpillar has one generation a year and over winter in the egg stage. In early spring, when deciduous trees begin to leaf out, larvae hatch from the eggs and feed on the emerging leaves. Western tent caterpillars find safety in numbers; the larvae aggregate together in communal silken tents during the night. Tents are usually formed in the crotches of smaller branches. Young larvae do not venture far from the tent and usually feed on the foliage of a single branch.

hatched egg mass

Newly hatched egg mass

young tent

Young larvae on newly constructed tent on apple

Western Tent CaterpillarThe Western tent caterpillar’s (Malacosoma californicum pluviale) body is dark with spots of white, orange and blue. White and orange-yellow tufts of hair poke out from each segment.



Forest CaterpillarThe Forest caterpillar is blue with spots of black, white and orange. The markings along the back resemble shoe-prints

As larvae mature, the caterpillars begin to become more solitary, feeding by themselves or in smaller groups. In June, the mature larvae wander away from the host tree and pupate by forming a white, puffy cocoon. After about ten days, adult moths emerge from the cocoon. Shortly after emerging, the adults mate. Adult moths are hairy, reddish-brown, stout moths. Often you will find these moths head-butting your porch light bulbs in June and July. Females seek new host trees to lay eggs on. Eggs are laid in frothy masses in batches of 100 to 350 on host tree branches. The eggs will stay glued on the tree until the larvae hatch next spring.

large tent
Larger larvae congregated on tent.

Cocoons spun in tall grass to pupate into adult moths.

adult tent caterpillar
Adult Western Tent Caterpillar
Return to Pest Pages
WSU Whatcom Co. WSDA Logo