There is a reason that the phrase, “pop goes the weasel,” is associated with this fast-moving mammal. They are quick, nimble, erratic and pop up in the most unexpected places, and usually for only a moment.
Weasels are in a family of animals called Mustelidae, or mustelids, with each member being ferocious predators. From the smallest in the family to the largest, each relies heavily on eating meat, with some members having the ability to take down an animal more than double its size.
The family includes animals like the short-tailed weasel, the long-tailed weasel, mink, pine marten, black-footed ferret, otter, fisher and wolverine. These animals are built with long, slender bodies and short legs, a design that allows them to follow their prey into dens and burrows.
The smallest of this family, and the smallest carnivore in North America, is the least weasel.
Found throughout Alaska, Canada and in the states of the upper Midwest and Great Lakes region, the least weasel is a very secretive animal that is only about 5-6 inches in length and weighs about one to two ounces. In winter, the least weasel has an entirely white coat but in summer, that coat molts to a warm brown while retaining the white or cream color on the belly. Least weasels have short tails – only about 15 percent of their body length – with no black tip.
The next size up in this family is the short-tailed weasel. A resident of Colorado, this small predator weighs only 1.5 to 6 ounces and is just slightly larger than the least weasel. Their range is larger than the least weasel, stretching from the East Coast to the West Coast in the northern U.S. states. This weasel can be identified by a black-tipped tail that is less than half the length of the head and body.
The third weasel in North America is the long-tailed weasel. More frequently seen than the previous two but not necessarily more abundant, the long-tailed weasel can be identified by a black-tipped tail that is more than half the head and body length. It too changes between a white coat in winter and a brown coat in summer but is the largest of the three, measuring up to 11 inches and weighting up to 10 ounces.
Dawn Wilson Photography
A long-tailed weasel runs acros the rocks of the tundra on Mt. Evans, Colorado. (Dawn Wilson Photography)
To make these three predators even more confusing to identify due to their similarities in appearance, all are often referred to as ermine when their coats convert to the winter white. The short-tailed weasel is really the only one that is accurately called an ermine in winter but the term seems to have stuck by many wildlife observers for the other species.
All three are extremely skilled predators. It is not unusual to hear about any of them capturing prey larger than themselves. Short-tailed weasels have been seen hunting pikas on the tundra and photos have proven that long-tailed weasels have skillfully caught snowshoe hares. To put those feats into perspective, the pika weighs up to 12 ounces, double the size of a short-tailed weasel, and can be up to 8 inches in length. The snowshoe hare can be up to 16 inches in length, with back feet alone that can be up to 6 inches, and can weight up to 3 pounds.
The other members of the mustelid family are just as versatile with their hunting skills.
Mink, which are often incorrectly mistaken for long-tailed weasels, have a coat that is all dark brown, sometimes with a small cream color patch under the chin. They do not change coat color in the winter. Mink are also more frequently seen near water, like rivers, lakes and creeks, where they hunt their preferred food of fish and crayfish.
Dawn Wilson Photography
An American marten looks out from some logs in the forest of northern Minn. (Dawn Wilson Photography)
Similar in appearance to the mink is the pine marten. Larger in size and with a sizable cream-colored patch on their chest, pine martens are shy forest animals that hunt almost any arboreal animal, including snowshoe hares, pine squirrels and voles.
Dawn Wilson Photography
A river otter looks out while crossing a frozen river in Wyoming. (Dawn Wilson Photography)
River otters are another member of the mustelid family. Weighing up to 24 pounds in a 31-inch body, otters live near water and prefer to hunt fish but will also eat frogs, crayfish and other aquatic species. They are excellent swimmers, often playing in water or sliding around on ice and snow along riverbanks in winter.
Other members of the weasel family, like the black-footed ferret, fisher and wolverine, can be found in North America but most are in limited ranges and their population numbers are feared to be in decline.
Black-footed ferrets, which can be found on the plains of Colorado, were thought to be extinct, but after a small population was discovered in Wyoming, their numbers have increased but only to about 350.
The fisher, which looks like an oversized marten, are found throughout Canada but in very limited populations in the U.S., mostly in New England.
Finally, the wolverine, which can sometimes be mistaken for a small bear when seen in the wild, is the largest member of the mustelid family in the U.S. Rare in Colorado, the wolverine population is estimated to only be about 300 animals in the Lower 48 states.
