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Lemmings Suicide Myth

The notion that lemmings, overcome by deep-rooted impulses, deliberately run over a cliff in their millions came not from a biologist, but from that other animal behaviourist - Walt Disney.

One myth deeply entrenched in our language is that of the "Lemming Suicide Plunge" - where lemmings, apparently overcome by deep-rooted impulses, deliberately run over a cliff in their millions, to be dashed to their deaths on the rocks below, or to drown in the raging ocean. Indeed, this myth is now a metaphor for the behaviour of crowds of people who foolishly follow each other, lemming-like, regardless of the consequences. This particular myth began with a Disney movie.

Lemmings belong to the rodents. Rodents have been around for about 57 million years. Today, about half of all the individuals mammals on Earth are rodents. There are four genera of lemmings - Collared Lemmings, "True" Lemmings, Wood or Red-Backed Lemmings and Bog Lemmings. They are found in the cooler northern parts of Eurasia and North America. The True Lemming is about 10 cm long, with short legs and tail.

Many of the rodents have strange population explosions. One such event in the Central Valley of California in 1926-27 had mouse populations reaching around 200,000 per hectare (about 20 mice per square metre). In France between 1790 and 1935, there were at least 20 mouse plagues. But lemmings have the most regular fluctuations - these population explosions happen every three or four years. The numbers rocket up, and then drop almost to extinction. Even after three-quarters of a century of intensive research, we don't fully understand why their populations fluctuate so much. Various factors (change in food availability, climate, density of predators, stress of overcrowding, infectious diseases, snow conditions, sunspots, etc) have all been put forward, but none completely explain what is going on.

Back in the 1530s, the geographer Zeigler of Strasbourg, tried to explain these variations in populations by saying that lemmings fell out of the sky in stormy weather, and then suffered mass extinctions with the sprouting of the grasses of spring. Back in the 19th century, the Naturalist Edward Nelson wrote that "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." But none of the Intuit stories mention the "suicide leaps off cliffs".

When these population explosions happen, the lemming migrate away from the denser centres. The migrations begin slowly and erratically, with an evolution from small numbers moving at night, to larger groups in the daytime. The most dramatic movements happen with the True Lemmings (also called the Norway Lemming). Even so, they do not form a continuous mass, but instead travel in groups with gaps of 10 minutes or more between them. They tend to follow roads and paths. Lemmings avoid water, and will usually scout around for a land crossing. But if they have to, they will swim. Their swimming ability is such that they can cross a 200 metre body of water on a calm night, but most will drown in a windy night.

So lemmings do have their regular wild fluctuations in population - and when the numbers are high, the lemmings do migrate.

The myth of mass lemming suicide began when the Walt Disney movie, Wild Wilderness was released in 1958. It was filmed in Alberta, Canada, far from the sea and not a native home to lemmings. So the filmmakers imported lemmings, by buying them from Inuit children. The migration sequence was filmed by placing the lemmings on a spinning turntable that was covered with snow, and then shooting it from many different angles. The cliff-death-plunge sequence was done by herding the lemmings over a small cliff into a river. It's easy to understand why the filmmakers did this - wild animals are notoriously uncooperative, and a migration-of-doom followed by a cliff-of-death sequence is far more dramatic to show than the lemmings' self-implemented population-density management plan.

So lemmings do not commit mass suicide. Indeed, animals live to thrive and survive. Consider a company like Disney, where one rodent, namely Mickey Mouse, was Royalty. It's rather odd to think that Disney could be so unkind to another rodent, the lemming...

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