Lemming

A lemming is a small rodent, usually found in or near the Arctic in tundra biomes. Lemmings form the subfamily Arvicolinae (also known as Microtinae) together with voles and muskrats, which form part of the superfamily Muroidea, which also includes rats, mice, hamsters and gerbils. They play an important role in the Arctic ecosystem, acting as grazers of mosses and grasses and as the primary prey (food) source for most Arctic carnivores. A longstanding myth claims that they exhibit herd mentality and jump off cliffs, committing mass suicide.

Description and habitat Lemmings measure around 13–18 cm (5–7 in) in length and weigh around 23–34 g (0.8–1.2 oz). Lemmings are quite rounded in shape, with brown and black, long, soft fur. They have a very short tail, a stubby, hairy snout, short legs and small ears. They have a flattened claw on the first digit of their front feet, which helps them to dig in the snow. 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. Lemmings choose their preferred dietary vegetation disproportionately to its occurrence in their habitat. They digest grasses and sedges less effectively than related voles. Like other rodents, they have incisors that grow continuously, allowing them to feed on much tougher forage. Lemmings do not hibernate through the harsh northern winter. They remain active, finding food by burrowing through the snow. These rodents live in large tunnel systems beneath the snow in winter, which protect them from predators. Their burrows have rest areas, toilet areas and nesting rooms. They make nests out of grasses, feathers, and muskox wool (qiviut). In the spring, they move to higher ground, where they live on mountain heaths or in forests, continuously breeding before returning in autumn to the tundra. Lemmings can live for up to twenty-four months although life expectancy is usually stated to be a year as a result of predation control.

Behaviour Like many other rodents, lemmings have periodic population booms and then disperse in all directions, seeking food and shelter their natural habitats cannot provide. The Norway lemming and West Siberian lemming are two of the few vertebrates which reproduce so quickly that their population fluctuations are chaotic, rather than following linear growth to a carrying capacity or regular oscillations. Why lemming populations fluctuate with such great variance roughly every four years, before numbers drop to near extinction, is not known. Lemming behaviour and appearance are markedly different from those of other rodents, which are inconspicuously coloured and try to conceal themselves from their predators. Lemmings, by contrast, are conspicuously coloured and behave aggressively toward predators and even human observers. The lemming defence system is thought to be based on aposematism (warning display). Fluctuations in the lemming population affect the behaviour of predators, and may fuel irruptions of birds of prey such as snowy owls to areas further south. For many years, the population of lemmings was believed to change with the population cycle, but now some evidence suggests their predators' populations, particularly those of the stoat, may be more closely involved in changing the lemming population.

Misconceptions Misconceptions about lemmings go back many centuries. In 1532, the geographer Jacob Ziegler of Bavaria proposed the theory that the creatures fell out of the sky during stormy weather and then died suddenly when the grass grew in spring. This description was contradicted by natural historian Ole Worm, who accepted that lemmings could fall out of the sky, but claimed that they had been brought over by the wind rather than created by spontaneous generation. Worm published dissections of a lemming, which showed that they are anatomically similar to most other rodents such as voles and hamsters, and the work of Carl Linnaeus proved that they had a natural origin.

Lemmings have become the subject of a widely popular misconception that they are driven to commit mass suicide when they migrate by jumping off cliffs or drowning in bodies of water. It is true that the local population of some lemmings fluctuates. Contrary to the myth, it is not a deliberate mass suicide, in which animals voluntarily choose to die, but rather a result of their migratory behavior. Driven by strong biological urges, some species of lemmings may migrate in large groups when population density becomes too great. Thus, the unexplained fluctuations in the population of Norwegian lemmings helped give rise to the popular stereotype of the suicidal lemmings, particularly after this behaviour was staged in the Walt Disney documentary White Wilderness in 1958. The misconception itself is much older, dating back to at least the late 19th century. In the August 1877 issue of Popular Science Monthly, apparently suicidal lemmings are presumed to be swimming in the Atlantic Ocean in search of the submerged continent of Lemuria.

Classification

Order Rodentia Superfamily Muroidea Family Cricetidae Subfamily Arvicolinae: voles, lemmings, and related species Tribe Dicrostonychini Dicrostonyx Northern collared lemming (D. groenlandicus) Ungava collared lemming (D. hudsonius) Nelson's collared lemming (D. nelsoni) Ogilvie Mountains collared lemming (D. nunatakensis) Richardson's collared lemming (D. richardsoni) Arctic lemming (D. torquatus) Unalaska collared lemming (D. unalascensis) Tribe Lemmini Lemmus Amur lemming (L. amurensis) Norway lemming (L. lemmus) Beringian lemming (L. nigripes) East Siberian lemming (L. paulus) West Siberian lemming (L. sibiricus) North American brown lemming (L. trimucronatus) Myopus Wood lemming (M. schisticolor) Synaptomys Northern bog lemming (S. borealis) Southern bog lemming (S. cooperi) Tribe Lagurini Eolagurus Yellow steppe lemming (E. luteus) Przewalski's steppe lemming (E. przewalskii) Lagurus Steppe lemming (L. lagurus)

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