The wash becomes less prominent on the sides, which are grayish. The underparts are dark slate gray to almost white. The tail has a slight terminal pencil of hairs. The short thumb is provided with a flat nail. The ears are slightly more conspicuous through the fur in Clethrionomys than in Microtus, and the eyes are also more prominent.
Females have eight mammae.
These rodents inhabit cold, mossy, rocky forests and woodlands in both dry and moist areas. They also inhabit tundra and bogs. They are active night and day, summer and winter, scurrying and climbing about stumps, fallen logs, and rough-barked trees. It does construct spherical nests of grasses, mosses, lichens, or shredded leaves. These nests are usually hidden under the roots of stumps, logs, or brush piles but may be located in holes or branches of trees high above the ground.