An ermine's home range is thought to be about 30-40 acres, and 20 individuals have been found per square mile of good habitat. In winter and early spring, ermines travel long distances for food, often 2-3 miles per night. In the northern part of its range, Mustela errninea lives in low brush and thickets along waterways in heavily forested areas. To the south, ermines inhabit open country with fencerows and rockpiles, brushy land and occasionally swamps. The long-tailed weasel is found from sea level to timberline from Maine across the United States and southern Canada, south to Florida, Mexico, and South America, excluding the U.S. Southwest.
Adult males are larger and heavier than females.
Sexes are colored alike. The dark brown tail is tipped black. Two molts occur each year. The fall molt is from October into November, the spring molt from mid-February or early March into April. Behavior of the long-tailed weasel is similar to that of the ermine.