Field Guide/Mammals/Ermine

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Mustela erminea (Ermine)
Family: Mustelidae
Size: Ranging in length from 7-14 inches (18-35cm) overall, with tail length, 2-6 inches (5-15cm) of total length or approximately 30-45% of the length of the body. Weight is 2-5 ounces (57-142g)[1][2]
Description: The ermine resembles a small weasel and exhibits a long slender body, a short tail, short legs and a pointed head with small rounded ears, round black eyes, long whiskers. Fur is reddish brown on the back and creamy white on the front or underside during warmer months; becoming all white in the winter.[1]
Similar Species: The ermine has a shorter tail than other weasel species and is slightly smaller overall. The mink is a much larger cousin to the ermine.[2]

Range: The ermine is widely populated in the northern portions of Europe, Asia, and North America. In the US they are mostly distributed north of a line between Oregon and Pennsylvania and throughout Minnesota, though there are known populations as far south as New Mexico. Ermines were also introduced in New Zealand but are not native to the islands.[3][4]
Habitat: Ermines can be found in all types of forests, prairies, farmlands, and tundra; essentially anywhere they can find a viable food supply – they do not avoid populations of humans. Because of their vulnerability to other predators they gravitate to areas that provide cover. Ermines are also adept at burrowing in the snow during winter. This provides insulation from the elements and camouflage as their fur changes to a white color during colder months.[3]
Diet: The ermine is an opportunistic predator and eats mice; voles; insects; fish; crayfish; small birds, rats and rabbits. They will also feed on garbage and decaying scraps left behind by other predators. Routinely ermines will peel away and discard the skin of their prey as they eat.[2][3]
Activity: Ermines nest in burrows, hollow trees, or rock piles. They are alternately active and resting for periods of 3-5 hours throughout a 24 hour period. They move quickly and in short bursts, investigating everywhere as they go. The climb trees and forage along streams and lakes. In the winter, hunting and activity is primarily in tunnels below the snow cover to avoid predators.[1]

Reproduction: Weasels, including the ermine, are somewhat unique. Their mating season is from the end of summer to mid-winter. The embryos grow for approximately two weeks and then go through a dormant period; development resumes for two more weeks in the spring and litters of 1-18 are born.[2][3]
Lifespan: Average life span is less than 12 months due to high juvenile mortality. However, natural life expectancy ranges from 2-3 years.[3]

Notes: The ermine is listed as one of the top 100 most invasive species in the world. It was introduced to several areas to reduce rabbit populations and rapidly became a threat to ecosystems because of its vicious nature and ability to sustain itself on a variety of prey.[3]


  1. a b c King, C (1983), "Mustela Erminea", Mammalian Species 195: (1–8),, retrieved (October 16, 2012) 
  2. a b c d Minnesota Department of Natural Resources ((2012)), Short Tailed Weasel (Ermine).,, retrieved (October 16, 2012) 
  3. a b c d e f IUCN/SSC Invasive Species Specialist Group (ISSG) ((2010)), Mustela Erminea,, retrieved (October 16, 2012) 
  4. "Mustela erminea", NatureServe, (2003),, retrieved (October 16, 2012)