Status: Common, Native Resident

(Mustela frenata)


The long-tailed weasel belongs to the Mustelid family, a group of mammals known for their long bodies, short legs, and strong scent glands. The Latin name is Mustela frenata refers to a bridle-like mask that is characteristic of weasel
populations in the southern United States, but lacking in South Dakota weasels. The Lakota word for weasel is (h)itunkasan. In summer the long-tailed weasel is brown with white underparts and brownish feet. The tail, the longest of any North American weasel, is brown with a black tip. This black tip confuses predators into mistaking the tail for the head, thereby drawing the focus of an attack away from the vulnerable portion of the body. During the winter, the weasel changes from the brown summer color to entirely white, except for the black of it's eyes, nose and tip of the tail. The color change in the weasels occurs gradually from early October to early December and then again from February to late April. These changes seem to be genetically controlled, not environmentally influenced. Experiments have shown that if a weasel from the northern regions is moved to the south, its coat will continue to change color according to the northern seasons

The body of the long-tailed weasel is long, slender, and sinuous, having a long tail and short legs. They range from 11 to 22
inches (28-56 cm) in length with the tail measuring an additional 3 to 6 inches (8-15 cm). The long-tailed weasel weighs
between 3 and 9 ounces (85-267 g) with males being about twice as large as the females. The weasel has between 28 and 38
teeth with long, sharp canines that it uses to deal the killing blow to a victim with a sharp bite to the back of the neck.

Long-tailed weasels range across much of the United States, southwestern Canada, and as far south as northern South
America. In South Dakota the species is found throughout the state. in 3 recognizable subspecies: M.f. alleni is the smallest
in size and is endemic to the Black Hills; M.f. spadix is the darkest in color and is found only in the eastern one-fourth of the state; and M.f. longicauda , the most common and largest in size, occupies the remaining areas in the state. The long-tailed
weasel shows a preference for open areas covered with brush or tall grass near water. Weasels live in dens made from
hollow logs, tree stumps, among rock piles, or in burrows that it has taken over by killing the former occupants. 

Natural History

The long-tailed weasel is an aggressive carnivore, preying primarily on mice, but also attacking animals much larger than
itself. Prey species include rabbits, chipmunks, shrews, rats, snakes, frogs, and birds, especially poultry. Weasels have even
been know to attack humans when being handled or when cornered. Not only is this species of weasel aggressive, but it
displays great agility and determination. In order to capture a squirrel, weasels have been known to climb 20 feet (6 m) up a

The weasel is prone to violent killing sprees. Weasels are notorious for killing entire coops of chickens. The killing instinct
in the weasel is thought to be brought on by the smell of blood. Nothing that is injured and in its vicinity is safe from attack.
Siblings and even their own young can be killed and eaten. It is a common misconception that weasels will suck the blood
out of its victims. This fabled ability stems from the fact that weasels being seen with blood on their snout after they have

The long and slender body of the weasel allows it to move, almost flow, over terrain. This body design makes it an effective
predator, able to follow its prey into the narrow tunnels of its den. Sometimes the weasel takes over the den of its prey and
will line the den with the fur of its victim. Long-tailed weasels can swim and climb quite effectively, but not with the
proficiency of its cousins the ermine and the fisher. Because of its slender body style, the weasel has a high metabolic rate.
In winter months it will use almost half of the food that it eats to maintain body heat. Weasels at rest will coil up with the
head to tail in the shape of a circle in order to conserve heat.

Female long-tailed weasels reach sexual maturity at 3 to 4 months of age, while males usually don't reach maturity until their
second year. Weasels may drag their rumps during mating season. This is thought to be a way of leaving scent trails for
members of the opposite sex. Males also use this scent to declare their territory to other males. Long-tailed weasels usually
breed in July or August and show the ability to delay the implantation of the embryo into the uterus for about 7 months after
fertilization. This delay is thought to be a adaptation to giving birth when conditions are at their most favorable. Litters, from
1 to 10 pups, are born in underground nests that are lined with rabbit or rodent fur. The young are born without fur and are
essentially blind. The nest is part of an elaborate underground den that has several branches, some serving as latrines and
others as food storage areas. The pups do not remain with the mother long. At 7 to 8 weeks, the male pups are already larger
than their mother and the young leave the den not long after.


Weasels do not pose a serious threat to humans other than threatening the poultry industry. Weasels are in fact a benefit in
that they destroy much of the rodent population that harms crops

Conservation Measures

Weasels are not considered an endangered species since they are found throughout the North American continent. The main
threats to weasels are often predators such as the gray fox, red fox, coyotes, hawks, large snakes and owls. Man is the
weasel's greatest enemy as weasels are taken for their pelts, even though the fur itself is not of great value.


Canines - the eye teeth found next to the incisors.
Carnivore - those animals that primarily eat meat.
Endemic - known only from a particular locality.
Subspecies - is a population of a species that is physically or behaviorly different from other populations of the species but
still capable of interbreeding with them.
Terrestrial - living on land.


Forsyth, Adrian, 1985. Mammals of the American North. Camden House Publishing Ltd. Toronto,
Jones, J. Knox, et al, 1983. Mammals of the Northern Great Plains. University of Nebraska Press. Lincoln, NE.
Nowak, Ronald M., 1991. Walkers Mammals of the World. Johns Hopkins University Press, Baltimore, MD.
Grzimek, H.C. Bernard, 1975. Grzimek's Animal Life Encyclopedia, Vol 12 (Mammals III). Van Nostrand and Reinhold
Company New York.
Whitaker, John O., 1980. The Audubon Society Field Guide to North American Mammals. Alfred A. Knopf Inc.

Written by:
Casey Dreis, biology student, Northern State University, Aberdeen, SD. 1997.

Illustrated by:

Kathy Colavitti, independent artist, Green Bay, WI.

Reviewed by:
Doug Bucklund, Resource Biologist, S.D. Department fo Game, Fish, and Parks, Pierre, SD.

Publication of the Long-tailed Weasel fact sheet was funded by the South Dakota Department of Game, Fish and Parks,
Division of Wildlife, Pierre, SD.