The long-tailed weasel has a small head with long whiskers, a long body and neck and short legs. Its tail has a black tip. It has brown fur on the upper part of its body and white to yellow fur on its undersides. In the northern parts of its range, it turns white in the winter. Adult males noticeably larger than females. Total length: 11 to 16.5 inches. Weight: three to 12 ounces. The footprint of a long-tailed weasel is about 1 inch long. Although they have five toes, only four of them can be seen in their tracks. The only exception to this is when walking in the snow or mud, all five of their toes are shown.

Found in almost all land habitats near water with the broadest range of the North American weasels. Prefers areas with abundant prey. Avoids dense forest, most abundant in late seral ecotones. Primarily nocturnal, but sometimes active during the day. Quite fearless and curious and terrestrial but can climb and swim well. Nests in old burrows of other animals with a diverse range of habitats. The enemies of the long-tailed weasel are usually coyotes, foxes, wildcats, wolves, and the Canadian lynx. The weasel will give off its musky odor, however, this is not primarily used when encountering other creatures. When leaving an area they were just in, they will leave their odor behind.