LEMMING, a small Scandinavian rodent, Lemmus lemmas, belonging to the mouse tribe (Muridae), and nearly related to the voles. About 5 in. long, the lemming is clad in yellowish-brown fur, marked with spots of black and brown. The head is short and rounded, the eyes bead-like and the short, rounded ears are almost concealed by the fur. The tail is short and the feet small, each with five claws adapted to digging. The lemming inhabits the fells of the central mountain chain of Scandinavia. They are prolific breeders, bringing forth at least two broods of, generally, five young in a year. Their food is entirely vegetable. In dispo sition they are restless, courageous and pugnacious. The most re markable feature about the lemmings is their migrations. These occur at irregular intervals, whenever an unusually favourable combination of circumstances had led to overcrowding on the fells. Then, impelled by a migratory instinct, the lemmings de scend into the lower levels in countless multitudes and proceed in a straight line until they reach the sea, into which they plunge and are drowned. They march only by night, feeding and sleeping by
day, and devour all vegetable food that comes in their way. This migration may take several years, and, notwithstanding the swarms of carnivorous mammals and birds that prey on them, and all the efforts of man, they breed with such prodigality as actually to increase in numbers during their journey. It has been suggested that this line of march is a survival from the old times when there was dry land over the Baltic and North seas.
Over east Europe, North Asia and North America, the genus is represented by the allied L. obensis, and in Alaska occurs L. nigripes. The circumpolar banded lemming, Dicrostonyx tor quatus, which turns white in winter, possesses double claws on one of the toes of the fore feet.
For the habits of the lemmings, see R. Collett, Myodes Lemmas, its Habits and Migrations in Norway.