Any of several species of small rodents belonging to the family Cricetidae and found primarily in northern temperate and polar regions of North America and Eurasia. Lemmings have short legs, small ears, and long, soft fur. They are 4–7 in. (10–18 cm) long, including the stumpy tail, and are grayish or reddish brown above, paler below. They feed on roots, shoots, and grasses and live in burrows or rock crevices. They are noted for regular population fluctuations, and for their periodic migrations in spring and fall. Those of the Norway lemming (Lemmus lemmus) are the most dramatic, because many of the migrants drown in the sea. However, lemmings are hesitant to enter water and, contrary to legend, do not plunge into the sea in a deliberate death march.
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Lemmings are small rodents, usually found in or near the Arctic, in tundra biomes. Together with the voles and muskrats, they make up the subfamily Arvicolinae (also known as Microtinae), which forms part of the largest mammal radiation by far, the superfamily Muroidea, which also includes the rats, mice, hamsters, and gerbils.
Lemmings do not hibernate through the harsh northern winter. They remain active, finding food by burrowing through the snow and utilising grasses clipped and stored in advance. They are solitary animals by nature, meeting only to mate and then going their separate ways, but like all rodents they have a high reproductive rate and can breed rapidly in good seasons.
There is little to distinguish a lemming from a vole. Most lemmings are members of the tribe Lemmini (one of the three tribes that make up the subfamily).
While for many years it was believed that the population of lemming predators changed with the population cycle, there is now some evidence to suggest that the predator's population may be more closely involved in changing the lemming population.
While many people believe that lemmings commit mass suicide when they migrate, this is not the case. Driven by strong biological urges, they will migrate in large groups when population density becomes too great. Lemmings can and do swim and may choose to cross a body of water in search of a new habitat. On occasion, and particularly in the case of the Norway lemmings in Scandinavia, large migrating groups will reach a cliff overlooking the ocean. They will stop until the urge to press on causes them to jump off the cliff and start swimming, sometimes to exhaustion and death. Lemmings are also often pushed into the sea as more and more lemmings arrive at the shore.
The myth of lemming mass suicide is long-standing and has been popularized by a number of factors. In 1955, Carl Barks drew an Uncle Scrooge adventure comic with the title "The Lemming with the Locket". This comic, which was inspired by a 1954 National Geographic article, showed massive numbers of lemmings jumping over Norwegian cliffs. Even more influential was the 1958 Disney film White Wilderness in which footage was shown that seems to show the mass suicide of lemmings. The film won an Academy Award for Documentary Feature.
Due to their association with this odd behaviour, lemming suicide is a frequently-used metaphor in reference to people who go along unquestioningly with popular opinion, with potentially dangerous or fatal consequences. This is the theme of the video game Lemmings, where the player attempts to save the mindlessly marching rodents from walking to their deaths.