western tent caterpillar moth

(Malacosoma californicum)


No Image Available

  Hodges #


Conservation Status
  IUCN Red List

not listed


N5 - Secure


not listed


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 1 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: 1 to 2 (35 to 50 mm)


Similar Species






One generation per year: Late July to early August






Life Cycle


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.


Larva Hosts


Many trees and woody shrubs


Adult Food




Distribution Map



21, 29, 30, 75.




Common in the west, uncommon in Minnesota



Lepidoptera (butterflies and moths)  


Bombycoidea (hawk, sphinx, silk, emperor, and allied moths)  
  No Rank Bombyciformes  


Lasiocampidae (lappet moths)  


Lasiocampinae (tent caterpillars)  





Subordinate Taxa


western tent caterpillar moth (Malacosoma californicum ambisimile)

western tent caterpillar moth (Malacosoma californicum californicum)

western tent caterpillar moth (Malacosoma californicum fragile)

western tent caterpillar moth (Malacosoma californicum lutescens)

western tent caterpillar moth (Malacosoma californicum pluvialis)

western tent caterpillar moth (Malacosoma californicum recenseo)




Malacosoma americana (an often repeated error in gender)


Common Names


western tent caterpillar

western tent caterpillar moth









Antemedial line

A thin line separating the basal area and the median area of the forewing of Lepidoptera.






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Other Videos
  Malacosoma californicum
Dennis Marlow

May 31, 2014

Western tent caterpillar are invading the Pacific Northwest! May2014

While opinions on tent caterpillars seem to vary, there is one thing no one seems to dispute — the little buggers are everywhere.

Estimated by experts to number in the billions, they're wiggling and munching their way across communities throughout Western Washington, and Whidbey Island is no exception.

Trees they plague, consuming leaves and coating branches like a moving bark, but nothing is out of reach: they cover mailboxes, parking lots, walls and even people can't seem to escape.

  Western Tent Caterpillars (Malacosoma californicum)
Wandering Sole Images

Jun 10, 201

Western tent caterpillars (Malacosoma californicum) near Saint Mary Lake in the East Kootenays of British Columbia.

  Tent Caterpillars on the March

Jun 26, 2012

The Western Tent Caterpillars are on the march. Colonizing new areas. Here they are crossing a bridge. They will have to negociate a busy road to get to new vegetation on the other side.

( Malacosoma californicum ) Vancouver, BC

  Western Tent Caterpillars on Tree Branch
Tony Zapien

May 4, 2013

Close up video of western tent caterpillars in Bellingham, WA on May 4th, 2013.

Malacosoma californicum, the western tent caterpillar, is a moth of the family Lasiocampidae. It is a tent caterpillar. It is found in the western part of the Nearctic ecozone.

The wingspan is about 28 millimeters.




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Created: 10/14/2019

Last Updated:

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