Lemmings

Lemmings are small mouselike rodents in the family Muridae, which also includes the voles, gerbils, hamsters, rats, and mice. Lemmings occur in open, northern habitats, especially in alpine and arctic tundra of North America and Eurasia. Lemmings are herbivores, feeding on sedges, grasses, berries, roots, and lichens. Lemmings are ecologically important in their habitat, in part because they are the major food of many species of predators.

Lemmings are highly fecund animals. When conditions are appropriate to their survival, some species of lemmings can become extremely abundant, an event that population ecologists refer to as an "irruption." When this happens, it seems that lemmings are everywhere, and indeed they are—they literally run over your feet in meadows, and may invade northern towns. Under these conditions the lemmings are driven to make short-distance migrations in search of food and new habitat.

Northern European legends about lemmings include references to mass migrations by these animals, in some cases including large numbers approaching seacliffs, jumping fearlessly into the ocean, and then swimming out toward the horizon until they become exhausted, and drown. These stories about mass migrations of lemmings are quite remarkable, but they may be somewhat embellished. There is no doubt, however, the some species of lemmings can periodically attain extraordinarily large populations, which then crash to smaller abundances, on about a three-to-five-year periodicity.

The true lemmings are four species in the genus Lemmus. The brown lemming (Lemmus sibiricus) occurs in alpine and arctic tundras of northern North America, and in Siberia. The Norway lemming (Lemmus lemmus) is most famous for its periodic irruptions. When these animals are abundant, they can literally eat most of the available food, causing their own starvation and that of other herbivores, including reindeer (Rangifer tarandus).

The collared or Arctic lemming (Dicrostonyx torquatus) is a widespread species of the Arctic tundra, occurring in both North America and Eurasia. Collared lemmings sometimes irrupt in abundance, and when this happens they are the focus of hunting of all predators, even those as large as wolves and bears. This species has a white pelage in the winter, but is brown during the brief, arctic summer.

The bog lemmings are North American species of moist habitats, especially Sphagnumbogs. The southern bog lemming (Synaptomys cooperi) occurs in the northeastern United States and southeastern Canada, while the northern bog lemming (S. borealis) ranges through most of forested Canada and Alaska.