Western tent caterpillar moth

Western tent caterpillar moth is common in western United States and western Canada, less common from Manitoba to Quebec. Isolated populations have been found in northern Minnesota, New Hampshire, and New York.

Adults have a wingspan of 1⅜″ to 2″ (35 to 50 mm). Males are highly variable in color. The may be almost entirely light, mostly light but with dark shading in the median area, or entirely dark. The forewings are usually medium-dark reddish-brown. There are two smooth lines: the antemedial line (AM line), between the basal and median areas; and the postmedial line (PM line), that separates the median area from the postmedial area. Aside from two white patches on the fringe, the forewings are otherwise unmarked. On light males, the AM and PM lines are dark, on dark males they are light. The female is light reddish tan and not as variable in color. The hindwings of both sexes are entirely reddish-brown with a faint median band.

The mature caterpillar is 1¾″ to 2″ long and highly variable in color. Most are pale blue. There is a broad black stripe on the upper middle (middorsal stripe) that has yellow and orange speckling. The speckling may be sparse or dense. In the center of the stripe on each abdominal segment there is a thin blue longitudinal line that does not quite reach the segment ends. The ground color is sometimes dark and the speckling coalesces into large reddish-orange spots. The body is covered with medium-length pale or orange hairs.

Wingspan: 1⅜″ to 2″ (35 to 50 mm)

One generation per year: Late July to early August

First stage (instar) larvae overwinter in the egg. Eggs hatch in the spring within two weeks of the bud burst of its host species. Early instar caterpillars create a silken group nest and feed within the nest. Late instars feed alone outside the nest. The mature in 30 to 42 days, pupate, and emerge as adults in late July to early August.

Many trees and woody shrubs

Malacosoma californicum
Dennis Marlow

Western Tent Caterpillars (Malacosoma californicum)
Wandering Sole Images

Tent Caterpillars on the March
wetvideocamera

Western Tent Caterpillars on Tree Branch
Tony Zapien