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Genus Malacosoma

Unknown Caterpillar - Malacosoma californica Forest Tent Caterpillar Moth - Malacosoma disstria Eastern Tent Caterpillar?? - Malacosoma americana Orange Moth - Malacosoma Forest Tent Caterpillar Moth (Malacosoma disstria)  - Malacosoma disstria Western Tent caterpillar - Malacosoma californica Caterpillar ~28mm - Malacosoma tigris Eastern Tent Caterpillar Moth - Caterpillar - Lateral  - Malacosoma americana
Show images of: caterpillars · adults · both
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Lepidoptera (Butterflies and Moths)
Superfamily Lasiocampoidea (Tent Caterpillar and Lappet Moths)
Family Lasiocampidae (Tent Caterpillar and Lappet Moths)
Subfamily Lasiocampinae
Tribe Lasiocampini
Genus Malacosoma
wingspan 22-44 mm
Adult: forewing variably light yellowish to dark brownish with either dark or pale straight AM and PM lines; hindwing similar but usually unmarked
throughout United States and southern Canada
M. americanum: eastern two-thirds of US and Canada, west to the Rockies
M. californicum: western two-thirds of US and Canada, east to Quebec
M. disstria: all of US and southern Canada
M. constrictum; incurvum; tigris: southwestern US
deciduous woodlands, edges, roadsides, treed yards and gardens; adults are nocturnal and come to light
larvae in spring
adults in late spring and early summer
larvae feed on leaves of various broadleaf trees and shrubs (varies according to species)
Life Cycle
one generation per year; overwinters as an egg
M. californicum egg mass on Red Alder (Alnus rubra) stem:
larvae of all species are social (gregarious), and all species except M. disstria construct silken tents within which the group rests when not feeding. These tents are generally constructed at nodes where branches/stems/trunks diverge (as opposed to Hyphantria cunea webs, which enclose the ends of branches).

Several species of flies and wasps parasitize the eggs, larvae, and pupae of the forest tent caterpillar. Most important are large gray flies, Sarcophaga aldrichi Parker, in the North; and S. houghi Aldrich in the South.

The gender of Malacosoma is neuter, so adjectivic species names ending -a are considered wrong spellings. (1)
Print References
Stehr, F.W. & E.F. Cook 1968. A revision of the genus Malacosoma Hübner in North America (Lepidoptera: Lasiocampidae): systematics, biology. immatures, and parasites. Bulletin of the United States National Museum. 276: 1-321. (1)
Internet References
pinned adult image thumbnails of 3 widespread species (CBIF)
The Social Caterpillars overview of larval habits plus links to images and info (Terrence Fitzgerald, State University of New York at Cortland)
live larva photos of 4 western species (Terrence Fitzgerald, State University of New York at Cortland)
distribution of world species plus foodplants, synonyms, links to images, references (Markku Savela, FUNET)
USDA. Fact sheet. Harold O. Batzer and Robert C. Morris.
Works Cited
1.A revision of the genus Malacosoma (Hubner) in North America (Lepidoptera: Lasiocampidae): systematics, ...
Frederick W. Stehr; Edwin F.Cook . 1968. Bulletin of the United States National Museum, 276: 1-321.