Lemming behavior and appearance are markedly different from those of other rodents, which are inconspicuously colored and try to conceal themselves from their predators. Lemmings, by contrast, are conspicuously colored and behave aggressively toward predators, even sometimes attacking humans.

Most lemmings are solitary creatures, meeting only to mate and then go their separate ways. When they do gather in groups, it's actually referred to as a slice of lemmings.

This misconception started with a National Geographic article on lemmings in 1954. Lemmings do migrate, and sometimes in vast numbers. The Norway lemming (Lemmus lemmus) migrates in huge hordes when the population becomes too large, with some of their number drowning when they are pushed into the sea by the pressing momentum of the masses behind them. But the notion of a deliberate death march into the sea is false.

Lemmings are found only in the Northern Hemisphere--usually in or near the Arctic tundra, which includes northern Canada, Alaska, Europe and Asia.

Lemmings do not hibernate through the harsh northern winter. They remain active, digging large tunnel systems beneath the snow to protect themselves from predators and find food. Their burrows have rest areas, toilet areas, and nesting rooms.

The color of collared lemmings varies seasonally. During the summer their coat is gray tinged with buff or reddish brown and with dark stripes on the face and back. In the winter, they molt into a white coat and develop forked digging claws.

The wood lemming (Myopus schisticolor) has an unusual genetic system that involves two different types of X chromosomes, the normal X and a mutated X*. Females with the mutated X*-chromosome inhibit the male determining effect of the Y chromosome. This leads to three genetic types of females: XX, X*X and X*Y and one genetic type of males XY.

They are herbivorous, feeding mostly on mosses and grasses. They also forage through the snow surface to find berries, leaves, shoots, roots, bulbs, and lichens.

Like other rodents, their incisors grow continuously throughout their lives. As a result, lemmings need to grind their teeth down to keep them from getting too large.

The 20 lemming species belong to 6 genera, which, along with voles and muskrats, are classified in the subfamily Arvicolinae of the mouse family (Muridae) within the order Rodentia.