† Incomplete listing: see vole[?]
Lemmings are small rodents, usually found in or near the Arctic. Together with the voles[?] and muskrats[?], they make up the subfamily Arvicolinae[?] (also known as Microtinae), which forms part of by far the largest mammal family, the Murinae[?], which also includes the rats, mice, hamsters, and gerbils.
Like voles, lemmings mostly weigh about 20 grams and are about 10 cm long. They usually have long, soft fur and very short tails. They are herbivorous, feeding mostly on leaves and shoots, grasses and sedges in particular, but also roots and bulbs in some cases. Like many rodents, their molars grow continuously, allowing them to exist on much tougher forage than would otherwise be possible.
Lemmings do not hibernate through the harsh northern winter, but remain active, finding food by burrowing through the snow, and utilising grasses cliped and stored in anticipation. They are solitary animals by nature, meeting only to mate and then going their seperate ways, but like all rodents they have a high reproductive rate and can breed rapidly in good seasons.
Lemming populations go through rapid growths and subsequent crashes that have achieved an almost legendary status, largely because of the well-known Disney Studios film, White Wilderness[?], which was produced in 1958 and reappeared on television at regular intervals for many years afterwards. White Wilderness was shot in Alberta, where there are no lemmings. However, the film makers arranged to buy wild-trapped lemmings from Inuit school children in Manitoba and transported them to the set, where they were placed on a large, snow covered turntable, spun until dizzy, and then filmed staggering about as if on a crazed migration. As a grand finale, the captive lemmings were herded over a cliff into a river (in the film, this was the "sea", and the herded lemmings were on a "suicide drive"). Generations of TV watching schoolchildren grew up on the Disney nature films, and the myth of lemming suicide persists to this day.
In fact, the behavior of lemmings is much the same as that of many other rodents which have periodic population booms and then disperse in all directions, seeking the food and shelter that their natural habitat cannot provide. (The Australian Long-haired Rat[?] is one example.) In typical years, the Norway Lemming[?] (which is the one that is said to be the suicidal species) spends the winter in nests under the snow. When the spring thaws begin and the snow starts to collapse, Norway Lemmings must migrate to higher ground where the snow is still firm enough for safety, or, more commonly, to lower ground, where they spend the summer months. In autumn, they must time their movement back to sheltered higher ground carefully, leaving after there is alpine snow cover for them to burrow and nest in, and before the lowlands are made uninhabitable by frost and ice.
When the seasons are particularly good—short winters without unexpected thaws or freezes, and long summers—the Norway Lemming population can increase explosively: they reach sexual maturity less than a month after birth, and breed year-round if conditions are right, producing a litter of 6 to 8 young every 3 to 4 weeks. Being solitary creatures by nature, the stronger lemmings drive the weaker and younger ones off long before a food shortage occurs. The young lemmings disperse in random directions looking for vacant territory. Where geographical features constrain their movements and channel them into a relatively narrow corridor, large numbers can build up leading to social friction, distress, and eventually a mass panic can follow, where they flee in all directions. Lemmings do migrate, and in vast numbers sometimes, but the deliberate march into the sea happens only in the fantasies of film makers.
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), but by no means all.