The ermine (or short-tailed weasel), Mustela erminea, occurs in much of northern North America, as well as in Eurasia. The species is relatively common in Utah, where it prefers heavily wooded areas along streams. Individuals are mainly active at night, and they may stay beneath the surface of the snow during much of the winter. Ermine dens can be found in hollow logs, in burrows, and under logs, roots, or rocks.
Females give birth to one litter of four to nine young during the spring of each year. The diet of the ermine is composed primarily of small rodents, although insects, birds, and other animals are also eaten. Ermine are brown with white bellies during the summer, but are almost completely white during the winter.