In the winter collared lemmings place their grass nests on the surface of the earth under a snowbank or even in the middle of a snowbank. They swim readily. In the winter they eat buds, twigs, and bark, and their summer diet consists of fruits, flowers, grasses, and sedges. Population densities fluctuate dramatically, from 0.6 per ha. At times these lemmings become so plentiful that they are forced to make short migrations in search of food, but they rarely make the lengthy mass movements sometimes observed in Lemmus.
Females are seasonally polyestrous and have a postpartum estrus.
They are very aggressive after giving birth, often attacking and occasionally killing males that attempt to mate with them. Without such aggressiveness, however, the males may kill the young already born. The beautiful white winter coat of Dicrostonyx is used by the Eskimos for garment trimming. The Eskimo children use the little skins to make doll clothes.