They can produce masses of offspring when conditions are right. They become sexually mature after a month, and produce about 10 offspring in each litter. With up to seven litters per year the numbers soon multiply. Every four years or so, their numbers build so much that overcrowding triggers a mass migration to search for new land. Travelling in large numbers over land is risky, and many starve or are eaten by predators. Lemmings can swim, but some do drown accidentally in the water. Hence, a grain of truth behind part of the Disney fabrication. But drowning is by accident not suicide. This boom and bust lifestyle might seem a strange path to follow. But lemmings need to be able to take rapid advantage of food supplies when it becomes available. Several animals living in harsh environments follow this strategy. Locusts in arid regions breed in large numbers when conditions are right, even though the population will crash when ill weather comes or the food runs out. In contrast, conditions in rainforests are far more stable, so you rarely see any one species building up in such numbers.
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They then placed the lemmings on a large turntable, like a 'merry-go-round' hidden with snow, and got the lemmings running. With some imaginative camera angles and editing, they made a few dozen lemmings look like thousands migrating and rushing to a scene even more startling. After the migration sequence, the lemmings were collected and taken to a cliff top overlooking a river. The documentary crew crouched down hidden from the cameras, and pushed the lemmings over the edge of the cliff to their death in the rushing water below. The myth of lemming suicide turned from fable to money-spinning 'fact'.
Of course, wild animals don't commit suicide. Their quality of life and freedom is better than humans seem to realise. But lemmings have an interesting biology that might appear to lead to population control through suicide. They are small rodents about 120 mm long, feed on plants and mosses, and during the winter live in burrows under the snow.
