Lemmings are rodents from the family Cricetidae, the second-largest family of mammals, which includes other rodents such as hamsters and voles as well as most of the wild rats and mice found in the Americas. While the 'true lemmings' of the genus Lemmus live in the tundras of the far North, in or near the Arctic circle, those of other genera are found as far afield as the deserts of China and Mongolia.

The Facts

Lemmings closely resemble voles and are often difficult to distinguish from them, or from one another. There are variations in size between species, but they generally range from 7-14cm in length (without tail) and weigh between 30g and 115g. They are usually mottled brown or grey with paler underbellies, though the collared lemming (genus Dicrostonyx) is the only rodent whose fur turns white in the winter. To conserve warmth they have thick fur and very short tails, with ears that can be folded close to their heads.

Like all rodents, they have incisors that grow continually. These teeth allow them to forage on roots and bulbs, along with their preferred diet of softer plant parts like shoots, grasses, and berries. Some species also eat small insects. Lemmings don't hibernate, but stay awake and alive all winter at temperatures as low as −25°C, burrowing deep under the snow¹ for warmth, and eating bark and twigs to stay alive. In times when food is scarce and competition strong, they have been known to turn cannibalistic, eating their own young or weaker members of their species.

Unlike many rodents, lemmings are solitary creatures. They are also creatures of habit, travelling the same routes every day (or night - they seem to have no set bedtimes) between their favourite food sources and their burrows, until they make recognisable paths and extensive systems of burrows and tunnels. Lemmings generally only come together to mate - and mate they do! Determined (or bored) animals can start as early as January, but the height of the breeding season is generally during the warmer summer months from June through September. During this time the females are nearly continually pregnant, usually bearing two to three litters with a general average of seven (but up to 13) young per litter. The gestation period is well under a month, and the young are sexually mature shortly after they start walking, at about two weeks!

The lemming is not found on Spitzbergen, but must at certain seasons occur in incredible numbers on Novaya Zemlya. For at the commencement of summer, when the snow has recently melted away, there are to be seen, everywhere in the level fertile places in the very close grass of the meadows, footpaths about an inch and a half deep, which have been formed during winter by the trampling of these small animals, under the snow, in the bed of grass or lichens which lies immediately above the frozen ground. [...] Thousands and thousands of animals must be required in order to carry out this work even over a small area[...]. During the snow-melting season these passages form channels for running off the water, small indeed, but everywhere to be met with, and contributing in a considerable degree to the drying of the ground. The ground besides is at certain places so thickly strewed with lemming dung, that it must have a considerable influence on the condition of the soil.
–  The Voyage of the Vega round Asia and Europe, Adolf Erik Nordenskiöld², 1881

These 'incredible numbers' of lemmings are a dietary staple for many Arctic predators like foxes, weasels, owls, wolves, wolverines, hawks, gulls, and falcons. They also have a relatively short natural lifespan, usually only one or two years³. This fast breeding and fast death means that at peak times, up to 30% of the lemming population can die off every two weeks!

The lemming population in any given area varies wildly, increasing up to tenfold in some years. The fluctuations seems to run in a cycle of three to ten years, and grow more extreme the further north their habitat is. Why this is has not yet been fully explained —  Canadian biologist Dennis Chitty devoted nearly six decades of his life to this phenomenon, and still has no answer, though several theories⁴, from available food sources to sunspots, have been discarded along the way. What he can disprove for certain is the popular misconception that lemmings regularly commit mass suicide by jumping off cliffs.

The Myth

The Norton Sound Eskimo have an odd superstition that the White Lemming lives in the land beyond the stars and that it sometimes comes down to the earth, descending in a spiral course during snow-storms.
– Edward William Nelson, American naturalist (*1855, †1934)

The 'death-by-drowning' myth is hardly the first theory put forward to explain the varying numbers of lemmings. In his 1532 treatise Quae intus continentur: Syriae, Arabia, Aegyptus, Schondia ... regionum superiorum, singulae tabulae geographicae⁵, Jacob Ziegler⁶ wrote that lemmings fall from the sky during the storms, and die when the first grass grows in spring. This fanciful belief was not refuted until the 17th Century, when the Danish physician Ole Worm made somewhat more scientific observations of lemmings.

However, the equally wrong belief that every seven years the lemmings migrate in herds by the hundreds, only to dramatically throw themselves off a sheer cliff-face at their destination, unstoppably determined to kill themselves, has stuck around much longer.

And Its Creation

The perpetuation of this myth can mostly be attributed to (or blamed on) Disney. The 1955 Uncle Scrooge adventure comic The Lemming With The Locket, drawn by Carl Barks, was allegedly inspired by a 1954 National Geographic article. It revolves around the frantic search for a specific lemming — one wearing a locket with the combination to a safe — rushing toward the sea with thousands of identical brethren, bent on taking its life.

Nobody can expect a story that features anthropomorphic cartoon ducks to be purely factual. The same cannot be said of a documentary, and one from the series 'True-Life Adventures' at that. And yet, following on from its 1953 success The Living Desert, Walt Disney Studios released White Wilderness in 1958, a film which won the Academy Award for Documentary Feature. Among the many spectacular nature scenes is a sequence depicting the frenzied migration and ultimate suicide of a horde of lemmings.

A kind of compulsion seizes each tiny rodent and, carried along by an unreasoning hysteria, each falls into step for a march that will take them to a strange destiny. [...] They've become victims of an obsession — a one-track thought: Move on! Move on! [...] They reach the final precipice. This is the last chance to turn back — yet over they go, casting themselves out bodily into space.
– Winston Hibler, narrating White Wilderness

Since lemmings don't naturally display this behaviour, the scene was constructed artificially. Filming took place in Alberta, Canada, which is landlocked and has no native lemming population. Instead, dozens of animals were bought from Inuit children in Manitoba, several provinces away. Most of the 'migration' took place on a snow-covered turntable, with the scenes of a handful of frightened rodents running away, cleverly cut together to look like an enormous number migrating across the snowy tundra. Finally, they were taken to a cliff by a river and flung down into the water to their deaths, the shot carefully composed to make the river seem like an ocean.

When this was revealed in 1983, it incensed both scientists and animal rights activists. Unlike The Living Desert, White Wilderness is not listed in the 'Movie Archive' on the official Disney website.

The Truth

So how did this myth start? Nobody's entirely sure when it happened, but the why was probably a combination of inaccurate observation of the natural world and the projection of human thoughts and motives onto the animals. Lemmings don't migrate — certainly not in packs — but when the population grows too large, they have been known to disperse into less favourable regions, like elk or beavers will. This may also help mix up the gene pool to prevent excessive inbreeding. Though they may move in the same general direction, they travel alone.

Like nearly every mammal, the lemming can swim — but it avoids water where possible. However, if they don't find an overland route, they will swim across. If the weather is cold or windy, or the body of water is very wide, they may accidentally drown during the crossing, or die of hypothermia when their undercoats become soaked — but they certainly aren't deliberately killing themselves! For the survival of the species, such a compulsion would be utterly counterproductive, ensuring that the toughest animals, who can make the long trek, are taken out of the gene pool. Like any animal, the lemming will fight to survive, and would rather kill its rivals than itself.

The classic example is in the Scandinavian mountains, where [lemmings] have been dramatically observed. They will come to a body of water and be temporarily stopped, and eventually they'll build up along the shore so dense and they will swim across. If they get wet to the skin, they're essentially dead.
– Gordon Jarrell, University of Alaska Fairbanks

To be fair, the Disney 'documentary' does describe the tale as one 'both true and false', and shows lemmings swimming away from the bottom of a cliff. The narrator explains that: 'it would appear that the lemmings consider this body just another lake, and if it's a lake, then it must have a farther shore⁷, and so they strike out boldly. [...] And so is acted out the legend of mass suicide, and the destruction of a species it would seem to be, except that Nature, in her infinite wisdom, has spared a few.' Unfortunately, it then goes on to teach its young viewers that the animals will willingly and consciously go to their deaths once more when the population grows too large.

Popular Culture

Unfortunately, the rather romantic legend of the suicidal lemmings persists to this day — in fact, it's the only thing most people associate with the animal! Besides becoming the subject of a computer game that centres on the premise of the lemmings' determined march toward suicide, they have become a metaphor, almost like the sheep, for unthinkingly following the crowd to certain destruction.

We have gone on piling weapon upon weapon, missile upon missile, helplessly, almost involuntarily, like the victims of some sort of hypnosis, like men in a dream, like lemmings heading for the sea.
– American diplomat George Kennan, describing the Cold War in 1981