Description
Ermine are small carnivores in the weasel family (Mustelidae). The major identification challenge is distinguishing ermine from long-tailed weasels and least weasels.
Long-tailed weasels are largest (total length 300-350 mm), ermine are medium sized (total length males 225-340 mm, females 190-290 mm), while least weasels are smallest (total length less than 250 mm in males and less than 225 mm in females; Svendsen, 1982). Long-tailed weasels have a tail longer than half their body length with a black tip, ermine have a tail length around a third of their body length with a black tip, and least weasels have a tail length around a quarter of their body length and lack a black tip. Only least weasel fur will fluoresce under ultraviolet light. Ermine and long-tailed weasels are more commonly detected in much of the Great lakes region, with least weasels less common.
Size
Measurements from Minnesota are from Hazard (1982), from Wisconsin are from Jackson (1961), and from the Eastern United States are from Hamilton and Whitaker (1998).
Total length averaged 12.1” (307 mm) in Minnesota males and 10.7” (272 mm) in Eastern United States males, and ranged from 11.4” to 13” (289-330 mm) in Minnesota males and from 9.9” to 11.6” (251-295 mm) in Eastern United States males. Total length averaged 9.9” (251 mm) in Minnesota females and 9.3” (236 mm) in Eastern United States females, and ranged from 9.2” to 11.2” (234-285 mm) in Minnesota females and 7.6” to 10” (194-255 mm) in Eastern United States females. Total length ranged from 9.4” to 13.4” (240-341 mm) in Wisconsin.
Tail length averaged 3.3” (85 mm) in Minnesota males and 2.8” (71 mm) in Eastern United States males, and ranged from 3.0” to 3.7” (75-94 mm) in Minnesota males and from 2.6” to 3.1” (65-80 mm) in Eastern United States males. Tail length averaged 2.6” (65 mm) in Minnesota females and 2.2” (55 mm) in Eastern United States females, and ranged from 2.1” to 3.0” (53-76 mm) in Minnesota females and 1.7” to 2.5” (44-64 mm) in Eastern United States females.
Male body weight averaged 0.25 lb (113 g) and ranged from 0.2 to 0.3 lb (91-142 g) in Minnesota, and averaged 0.2 lb (80 g) in Eastern United States. Female weight averaged 0.2 lb (75 g) and ranged from 0.1 to 0.3 lb (43-125 g) in Minnesota, and averaged 0.1 lb (54 g) in Eastern United States.
Males are typically larger than females.
Distribution & Status
Ermine are found from the Arctic into the Northeast United States, Great Lakes region, Pacific Northwest, Intermontane West, and Northern California. Ermine can be found in a variety of habitats, including forest, tundra, and plains. Populations are secure or apparently secure throughout the Great Lakes region.
Worldwide, Mustela erminea is the most widespread weasel species, and is found throughout northern Asia, Europe, and North America. Other Mustela species occur throughout the world, except for Australia, Antarctica, and most oceanic islands.
Ermine have an IUCN rank of Least Concern, IUCN information
Incidence in Minnesota
Weasels, including ermine, are classified as unprotected species in Minnesota. Hunting and trapping are regulated by the Minnesota Department of Natural Resources, regulations here.
From winter track data (1994-2015) it appears that Minnesota weasel populations are declining (Erb, 2015).
Population Trends
To help assess population trends, we can look at regional furbearer harvest data, methods.
Harvest data for ermines, long-tailed weasels, and least weasels are pooled as “weasels”, making it difficult to isolate individual species trends. Of the three pooled species, ermine are the most abundant over most of the Great Lakes region. There is a lot of year-to-year variation in harvest, making it difficult to detect any long-term trends.
Minnesota and Ontario dominate regional harvest, with Wisconsin harvest increasing significantly since the mid-1990s.
Life History
Ermine primarily prey on voles and mice, but will also take other small mammals, reptiles, amphibians, birds, and invertebrates. Ermine breed in mid-summer, but have a delayed implantation, with a resulting 8-9 month gestation. Females bear 4-9 young in April, with young eyes and ears opening at 5 weeks, and young dispersing by the end of summer. Dens are in vacant chipmunk holes, or in brush/rock shelters. To hunt, ermines will burrow under snow, and use snowshoe hare runways and pocket gopher burrows (Chapman and Feldhamer, 1982). Ermines will cache excess food for later use. Ermines in northern climes are brown in summer, and turn white in winter. Ermine are prey for raptors, larger mammal carnivores, and snakes.
Contacts with Humans
Ermines and other weasels are trapped for their pelts. Weasels are sometimes viewed as threats to poultry operations, but rarely attack domestic fowl. Weasels help control mice, voles, and other small mammal populations that can be pest species to humans.