Natural Histories

photograph of a Sunda Pangolin

Least Weasel

Mustela nivalis


Least weasels have long, slender bodies with short limbs, a long neck and a flat, narrow head. They have large black eyes and large round ears. This species has five fingers with sharp claws. Their fur is a milk-chocolate brown with white on the under parts. Northern populations have a white winter coat and brown summer coat. The least weasel is less than 10 inches long and only weighs one to three ounces.


Least weasels may be found in many places including most of the Palearctic region (except Ireland, Arabian Peninsula, and the Arctic Isles), Japan, North Africa, the Nearctic (from Alaska and Northern Canada south to Wyoming and North Carolina). New Zealand also has a population that was introduced by humans. They live in a variety of habitats including open forests, farmlands, meadows, prairies, steppe, and semi-deserts. They do not prefer deep forests, sandy deserts, or open spaces. They are particularly adapted to living in the tundra. Dens of least weasels are shallow dens only 5 inches underground, often taken from prey animals.

Feeding Behavior and Diet

This species watches their prey before attacking. Least weasels target the neck of their prey. They prey mostly on small mammals (mainly rodents), but they will also consume bird’s eggs and nestlings, also the occasional lizard and insect. The males are able to hunt larger prey than the females. In the northernmost populations, least weasels have been documented to eat the carcasses of brown lemmings.


Breeding can occur throughout the year but mostly takes place in spring and late summer. Thirty four to thirty seven days after mating, the female gives birth to 1-7 young. Northern populations tend to have larger litters. Young reach adult size by 49-56 days, by 6 weeks the males are larger than the females. The mother cares for and nurses the young until they are independent after 9-12 weeks. Males reach sexual maturity at ten months old. Sexual maturity is reached by females born in the spring and can breed by the first summer. Females born in summer and fall are not as well developed and cannot breed until the following summer. A female will generally produce two to three litters per year.

Months and Times of Activity

This species is mainly solitary, except during breeding season. Least weasels may be active during the day but do most of their hunting at night.

Special Features, Stories, Relationships

  • Least weasels are very aggressive and will defend their territory, attacking much bigger animals when necessary.
  • The least weasel is the smallest carnivore in North America.
  • To read legends about this animal please go to:
  • Children’s book featuring the least weasel: Welkin Weasels by Garry Kilworth


"Montana Field Guides, Least Weasel." Montana Natural Heritage Program & Montana Fish, Wildlife and Parks, n.d. Web. 11 Feb. 2013.

Campbell, G. 2014. "Mustela nivalis" (On-line), Animal Diversity Web. Accessed November 04, 2014 at