A lemming is a small, yellowish-brown rodent, closely related to the vole, and belonging to the genus Myodes. The Norwegian lemming (M. lemmus) is about five inches in length, with the tail extremely short. It excavates shallow burrows in the soil of the mountain meadows in which it lives, and in winter tunnels beneath the snow for its food, which is wholly vegetable, consisting of roots, shoots, catkins, moss, and lichens. Special interest attaches to this rodent from the fact that at irregular intervals, varying from five to twenty years, it suddenly appears in vast numbers in Northern Europe; great bodies, said to number millions of individuals, migrate from place to place in search of food, leaving behind them a track of desolation as they eat their way through fields of corn and grass. They show a remarkable persistency both in the act of migration and in the general direction of the movement, and swim without hesitation any bodies of water which may block their path. As, from the contour of the Scandinavian peninsula, they inevitably come eventually to the sea, those which have not perished from overcrowding, from disease, or from the attacks of their enemies, die in attempting to swim across it. The lemming of Northern Europe is known is replaced in North America by the allied M. obensis and the banded lemming (Cuniculus torquatus); the latter is circumpolar, and turns white in winter. Other allies, called lemming-mice, inhabit Northwestern Canada, and have somewhat similar habits, but rarely, if ever, migrate from their habitat.
John H. Finley ed. Nelson's Perpetual Loose-Leaf Encyclopaedia (vol. 7) (New York, NY: Thomas Nelson and Sons, 1917) 273