lemming, name for several species of mouselike rodents related to the voles. All live in arctic or northern regions, inhabiting tundra or open meadows. They frequently nest in underground burrows, particularly in winter, although they do not hibernate. They feed on grasses, mosses, and roots, and probably on insects. All are about 5 in. (13 cm) long, with stout bodies, thick fluffy fur, small ears, very short tails, and long claws. The brown to black Norway lemming, Lemmus lemmus, of Scandinavia, is the best known, because of its spectacular periodic swarming. Two or three times per decade, this species undergoes a population explosion of such proportions that the lemmings set out in all directions in search of food. They cross bodies of water by swimming and occasionally some reach and enter the ocean, where they drown. This behavior has given rise to folklore about lemmings committing mass suicide, but the population crashes mainly because lemming predators increase in number in response. Other species of the genus Lemmus are found in the northern portions of Eurasia and North America and sometimes exhibit similar swarmings. The snow, or collard, lemmings, Dicrostonyx, found in the arctic regions of Asia and North America, are pure white in winter and brown, gray, or reddish in summer; this color change is unique among rodents. They are also distinguished by the growth in winter of an extremely long two-pronged claw on the third and fourth finger of each forefoot; these claws may function in shoveling snow. Bog lemmings, members of the genus Synaptus, are found in marshy places in North America as far south as the N United States. The wood lemming, Myopus schisticolor, is found in N Eurasia. The steppe lemmings, members of the genus Lagarus, of S Russia and Mongolia, are properly classified as voles; the North American species of this genus, Lagarus curtatus, is found in the W United States and is known as the sagebrush vole. Lemmings are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Rodentia, family Cricetidae. See mouse.