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least weasel

least weasel (Mustela nivalis) Photo provided by StephanMorris/

Features and Behaviors


The least weasel is small, rarely exceeding 10 inches in length. Its tail is about one to one and one-half inches long. This animal has a long, narrow body with short legs. During the summer, the fur on its back, sides, tail and top of the head is red-brown, and the rest of its body fur is white. In the winter, the fur may be all white. Fall and spring fur colors are a mix of the summer and winter versions as the transition in color is made. The ears are small and round.


The least weasel may be found in the northern one-half of Illinois. It lives in grassy fields railroad rights-of-way or the edges of cultivated fields. This mammal eats small birds, invertebrates, mice, ground squirrels, rats and voles. It may kill more mice and voles than it needs at one time and store them for later. This weasel probably relies greatly on its sense of smell because it seems to have poor eyesight. When disturbed, it may release a musky odor and make a shrieking noise. The least weasel may take over and use the nests of other small mammals. Breeding may occur at any time of year but seems to be most common in spring. The gestation period is about one month, and the average litter size is five. Two or more litters may be raised in one year. Young are helpless at birth but develop rapidly. Young females attain sexual maturity at the age of about four months, while males become sexually mature at about eight months of age.

Illinois Range


​Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Mustelidae

Illinois Status: common, native