The gender of Malacosoma is neuter, so adjectivic species names end -um instead of -a, or -e instead of -is.

Stehr, F.W. & E.F. Cook 1968. A revision of the genus Malacosoma Hubner in North America (Lepidoptera: Lasiocampidae): systematics, biology, immatures, and parasites. Bulletin of the United States National Museum, (276): 1-321.