The long-tailed weasel (Mustela frenata) is the most common carnivore in North America. Though these weasels inhabit a variety of habitats, from upland brush and woods to semi-open forest areas, in Idaho they are most often found in rocky, mountainous regions.  The are frequently seen on in the INL.

The long-tailed weasel has a long and slender body, brown fur, short legs, and a tail measuring up to seven inches in length. The tail, the longest of any North American weasel, has 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 its eyes, nose and tip of the tail.

Long-tailed weasels also have between 28 and 38 long, sharp teeth that they use to deliver a sharp, killing bite to back of their prey’s neck. They find prey mainly by scent, darting in and out of rodent burrows, checking brush, and rock crevices. Their long, thin body makes it easy for them to follow its prey into burrows.

Because of the weasels’ slender body shape, they don’t store heat well and have a very high rate of metabolism. They may eat about 40 percent of their body weight every day! Most of their diet is made up of small mammals like mice, voles, rabbits, gophers and chipmunks. They will occasionally eat birds and insects.

The Long-tail was once thought to be primarily nocturnal, but evidence has shown that they may hunt during daylight hours, as well, especially during the summer. Long-tail weasels do not hibernate, and often will kill more animals than they can eat at one time and cache the carcasses for later. Weasels occasionally go on killing sprees, as instinct dictates that they procure food when available and then store it. For this reason, a weasel in a chicken yard is disastrous. Although they are notorious for destruction of poultry, the damage they do is far outweighed by their value as destroyers of rodents, however.

Weasels are curious and bold and will often stand up on their hind legs for a better look at you if you avoid any quick movements.  They make a rapid "took-took-took" sound, hiss, purr, chatter, grunt and screech. When annoyed, they stamp their feet or emit musk from their anal scent glands.