American ermine
Near Beaverhill Lake, Alberta

Secure (NatureServe)[1]
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Mustelidae
Genus: Mustela
M. richardsonii
Binomial name
Mustela richardsonii
Bonaparte, 1838

See text

  • Mustela erminea richardsonii
  • Neogale richardsonii

The American ermine or American stoat (Mustela richardsonii) is a species of mustelid native to most of North America.


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.[2][3][4] The finding has been accepted by the American Society of Mammalogists.[5] The Haida ermine (M. haidarum) is thought to be a hybrid species originating from ancient hybridization between M. erminea and M. richardsonii.[2]


The specific epithet refers to Arctic explorer and naturalist John Richardson.


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.[2]


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, young cottontails,[6] chipmunks, deer mice, jumping mice, and house mice. Usually the ermine kills by biting at base of skull. Small birds, frogs, small fish, and earthworms are other types of prey for ermines.[7]


Ermines live and find cover from predators in hollow spaces from logs, burrows and man made structures. Ermines sometimes den within their prey's nest and use their skin and fur as a lining for their den.[7]


They breed in dense parts of the forest. The season for breeding is late springtime to the summer from July to August. The males mature in a year while the females only take three to four weeks to mature. The females carry a litter of four to seven babies for 255 days then gives birth.[1]


Some of the larger wild predators of ermines are minks, martens, fishers, bobcats, coyotes, and large owls and hawks. Occasionally a domesticated cat or dog may kill an ermine. Their small agile bodies help them evade these predators, while also allow them to compete with their predators for food in more barren months.[7]


About 13 subspecies are known:

Subspecies Trinomial authority Description Range Synonyms
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[8] 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.[9] 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[9] 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 was 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 made into shirts.[10]



  1. ^ a b "NatureServe Explorer 2.0". Retrieved 31 October 2022.
  2. ^ a b c 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.
  3. ^ "Distinct Species of Adorable Weasels Have Been Hiding in Plain Sight". Gizmodo. 13 April 2021. Retrieved 2021-07-12.
  4. ^ "Adorable Killer Ermines Found To Contain Three Distinct Species Of Fluffy Weasels". IFLScience. Retrieved 2021-07-12.
  5. ^ "Mustela richardsonii Bonaparte, 1838". Retrieved 2021-07-12.
  6. ^ Verts & Carraway 1998, p. 417
  7. ^ a b c Ahlborn, G. “Life History Account for Ermine.” Life History Accounts for Species in the California Wildlife Habitat Relationships (CWHR) System, 1988.
  8. ^ Merriam 1896, pp. 12–13
  9. ^ a b Merriam 1896, pp. 11–12
  10. ^ "Tlingit Ermine-Skin Shirt (Daa dugu k'oodas')".