It was long considered conspecific with the stoat (M. erminea), but a 2021 study found it to be a distinct species, forming distinct genetic clades from erminea. The finding has been accepted by the American Society of Mammalogists. The Haida ermine (M. haidarum) is thought to be a hybrid species originating from ancient hybridization between M. erminea and M. richardsonii.
The species is found throughout most of North America aside from most of Alaska (although it is found on some islands in southeastern Alaska), eastern Yukon, most of Arctic Canada, and Greenland, where it is replaced by M. erminea. It reaches the northern extent of its range in Baffin Island and a portion of eastern mainland Nunavut and ranges from here to cover almost all of western North America south to northern New Mexico, and eastern North America south to northern Virginia. It is absent from most of the Southeastern United States and the Great Plains.
In North America, where the ecological niche for rat- and rabbit-sized prey is taken by the larger long-tailed weasel (Neogale frenata), the American ermine preys on mice, voles, shrews, and young cottontails.
About 13 subspecies are known:
|Junean stoat |
M. r. alascensis
|Merriam, 1896||Similar to M. r. richardsonii, but with a broader skull and more extensive white tips on the limbs||Juneau, Alaska|
|Vancouver Island stoat |
M. r. anguinae
|Hall, 1932||Vancouver Island|
|Western Great Lakes stoat |
M. r. bangsi
|Hall, 1945||The region west of the Great Lakes||cicognani (Mearns, 1891) |
pusillus (Aughey, 1880)
|Bonaparte's stoat |
M. r. cigognanii
|Bonaparte, 1838||A small subspecies with a dark brown summer coat; its skull is more lightly built than that of richardsonii.||The region north and east of the Great Lakes||pusilla (DeKay, 1842) |
vulgaris (Griffith, 1827)
|M. r. fallenda||Hall, 1945|
|M. r. gulosa||Hall, 1945|
|M. r. initis||Hall, 1945|
|M. r. invicta||Hall, 1945|
|Southwestern stoat |
M. r. muricus
|Bangs, 1899||The southwestern extremity of the species' American range (Nevada, Utah, Colorado and other states)||leptus (Merriam, 1903)|
|Olympic stoat |
M. r. olympica
|Hall, 1945||The Olympic Peninsula, Washington|
|Richardson's stoat |
M. r. richardsonii
|Bonaparte, 1838||Similar to M. r. cigognanii, but larger, with a dull chocolate brown summer coat||Newfoundland, Labrador and nearly all of Canada (save for the ranges of other American stoat subspecies)||imperii (Barrett-Hamilton, 1904) |
microtis (J. A. Allen, 1903)
mortigena (Bangs, 1913)
|Baffin Island stoat |
M. r. semplei
|Sutton and Hamilton, 1932||Baffin Island and the adjacent parts of the mainland||labiata (Degerbøl, 1935)|
|M. r. stratori||Merriam, 1896|
Relationships with humans
The fur of ermine (both M. erminea and M. richardsonii, both of which inhabited the Tlingit's territory) were valued by the Tlingit and other indigenous peoples of the Pacific Northwest Coast. They could be attached to traditional regalia and cedar bark hats as status symbols, or they were also made into shirts.
- Colella, Jocelyn P.; Frederick, Lindsey M.; Talbot, Sandra L.; Cook, Joseph A. (2021). "Extrinsically reinforced hybrid speciation within Holarctic ermine (Mustela spp.) produces an insular endemic". Diversity and Distributions. 27 (4): 747–762. doi:10.1111/ddi.13234. ISSN 1472-4642.
- "Distinct Species of Adorable Weasels Have Been Hiding in Plain Sight". Gizmodo. Retrieved 2021-07-12.
- "Adorable Killer Ermines Found To Contain Three Distinct Species Of Fluffy Weasels". IFLScience. Retrieved 2021-07-12.
- "Explore the Database". www.mammaldiversity.org. Retrieved 2021-07-12.
- Verts & Carraway 1998, p. 417
- Merriam 1896, pp. 12–13
- Merriam 1896, pp. 11–12
- "Tlingit Ermine-Skin Shirt (Daa dugu k'oodas')".