Fall Webworm

Description:

"Fall webworm generally has one generation per year in the Rocky Mountain Region. Adults appear from late June to early July, fly at night, and lay eggs on the underside of leaves. After hatching, the young larvae feed gregariously, at first on the epidermis but not the veins of both leaf surfaces, producing a skeletonized pattern. As the larvae grow, they begin to feed on entire leaves, spinning silk wherever they go. Eventually, they enshroud leaves and then whole branches in a loosely spun tent of silk, within which larval development and feeding occurs, so that leaf fragments, cast skins, and droppings become incorporated. The larvae, when disturbed, often twitch and wave their bodies synchronously in what is thought to be predator avoidance. Feeding continues until mid-September, when full-grown larvae wander from their host plant in search of protected pupation sites."