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Mammals

Weasels

Photo: Sheila Newenham
Young least weasel on a wooden deck.
Young least weasel

Did You Know?

  • Both least weasels and long-tailed weasels are good at climbing trees. Long-tailed weasels are strong swimmers.
  • During the winter both species of weasel have lighter fur than during the warmer months. They may have all-white fur during the winter months, especially in northern Illinois.
  • Despite their small size, both types of weasel are fierce predators.

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Positive Benefits

Both least and long-tailed weasels prey on mice, voles, ground squirrels and rabbits, helping to maintain a balance in these small mammal populations.

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Description & Identification

Two species of weasel are found in Illinois—the least weasel (Mustela nivalis) and the long-tailed weasel (Mustela frenata).

Photo: Javan Rhino, ZooChat
Least weasel. Note the short tail.
Least weasel. Note the short tail.

The long-tailed weasel is two to three times larger than the least weasel. Both weasels have long, slender bodies, wide heads with small rounded ears and short legs. Long-tailed weasels are 11 to 17 inches long and weight between three and 10 ounces. Their tails are nearly half the length of their bodies and tipped with black fur. Least weasels can grow to 10 inches and weigh only one to three ounces. Their tails are less than a fourth of the length of their bodies and do not have a black tip. Males are larger than females in both species.

Photo: Keith and Kasia Moore, Flickr CC BY-SA 2.0
Long-tailed weasel. Note the black-tipped tail. Least weasels are smaller and do not have the black tip.
Long-tailed weasel. Note the long, black-tipped tail. Least weasels are smaller and do not have a black tip at the end of their tail.

In the summer, both species have reddish-brown fur with a yellowish-white throat, chest and underside, and the long-tailed weasel has a black-tipped tail. In the fall, weasels shed this coat and grow fur that is lighter, in many cases totally white (except for the black tip on the long-tailed weasels’ tails). In the winter, weasels found in northern Illinois are often white to help them blend into snow-covered landscapes, while those in southern Illinois may have patches of brown and white or their solid reddish-brown coat.

Photo: Marko Kivelä
Least weasel in it's white winter coat.
Least weasel in it’s white winter coat.

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Size Comparison

Illustrator: Lynn Smith
Man and weasel illustration
Size comparison of a six-foot tall man, a long-tailed weasel and a least weasel.

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Signs: Tracks & Scat

Both weasels have five toes on each paw, but the inner toe does not always register in the tracks of the least weasel. The long-tailed weasel has tracks that are 1 to 1.8 inches long and 0.8 to 1 inch wide. The least weasel has tracks that are 0.5 to 0.8 inches long and 0.4 to 0.5 inches wide. Both move with a loping gait that produces paired tracks, front paws together and rear paws together. The rear tracks are close to, or sometimes cover, the front tracks.

Weasel scat is dark, thin and twisted, about an inch long and tapered at both ends. It often contains fur, pieces of bone or insect parts. The scat is typically found on logs, rocks or near the den entrance.

Ann Schletz
Long-tailed weasel scat.
Long-tailed weasel scat.

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Distribution & Abundance

Long-tailed weasels are found throughout Illinois and are fairly common. Least weasels are only found in the northern half of the state and are not often seen, even though they may be common in the area.

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Behavior & Ecological Role

Weasels are active during the day and night, alternating between hunting and resting periods. Both species follow regular hunting routes, but only cover part of their homeranges during a single night. Males travel farther than females.

Photo: Bryant Olsen, Flickr CC BY-NC 2.0
Long-tailed weasel with a mouse.
Long-tailed weasel with a mouse.

Small prey are killed with a few quick bites to the back of the neck. When a weasel finds prey in tunnels or underground burrows, the prey is attacked head-on and killed by a bite to the windpipe.

Weasels bound or lope with their backs arched and their tails held straight out or slightly higher than their back. They swim well and climb trees easily. Least weasels often stand on their hind legs to survey the area around them.

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Diseases & Public Health

Weasels do not pose a public health threat.

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Habitat & Food

Weasels are habitat generalists but tend to prefer being near water.  Long-tailed weasels are more tolerant of people and will live on farms or the edges of suburbs. They prefer to live in forests, woodlands, thickets or brushy fence rows. Least weasels prefer more open areas like meadows, grasslands or river bottoms.

Weasel dens are usually found in rock piles, junk heaps, abandoned buildings or burrows dug by other animals. The size of the area they live in depends on the amount of food found there. When small mammal populations are large, the home range of a least weasel can be as small as 1.5 to 2.5 acres but expands to 37 to 65 acres when food is scarce. The home range of a long-tailed weasel can vary from 25 to 400 acres depending on food supplies.

Least weasels are more specialized hunters than long-tailed weasels, focusing on voles and mice. Long-tailed weasels eat mice, rats, voles, squirrels, chipmunks, shrews, moles and rabbits. Less common foods include birds, bird eggs, snakes, frogs and insects. Both species kill more than they can eat and cache (store) the prey for later.

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Reproduction & Longevity

Long-tailed weasels mate in July or August, and the young are born the following April or May. Females have only one litter per year, which range from one to nine young, though the average litter size is four to five. The female cares for the young alone. The young begin hunting with their mother when they are around 6 weeks and leave to find their own territories when they are just 11 to 12 weeks old.

Photo: Wayne Walker
Four least weasel young.
Four least weasel young.

Least weasels breed year-round. Females can have up to three litters per year if plenty of prey is available, and they care for the young alone. The average litter is four to five young. Young least weasels develop quickly when food is plentiful.  Females born early in the year can breed as soon as 4 months of age.

Neither species lives very long, typically less than a year.

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Damage Prevention & Control Measures

Weasels will readily kill poultry if they can get into the enclosure. However, they are often attracted to sites by mice or rats.

Habitat Modification

Habitat modification is not an efficient way of controlling weasels.

Exclusion

The best defense against weasels is to keep them out. Poultry houses must have a roof, and all holes or openings larger than 1 inch should be covered using ½ inch hardware cloth.

Repellents & Frightening Devices

There are no registered repellents for use against weasels in Illinois.

Frightening devices are ineffective against weasels.

Removal

Least weasels and long-tailed weasels are protected as furbearers in Illinois. If a weasel is causing damaging, you may remove the weasel if you have received an animal removal PERMIT from an Illinois Department of Natural Resources district wildlife biologist. Weasels may not be hunted in Illinois, but they can be trapped mid-November through mid-February. No. 0 or 1 steel leghold traps or live-traps baited with fresh meat are effective. Click HERE for full trapping regulations.

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