Poor lemming. Even though the old myth—that these Arctic rodents commit mass suicide—has been busted for a long time, some people still believe it. Where did the myth come from? Lemming populations fluctuate dramatically, following a roughly four-year cycle. For this reason, they have a huge impact on the lives and survival of almost everyone else living in the treeless, Arctic tundra, including birds of prey, foxes, and ermines. For example, research shows that both snowy owls and Arctic foxes only produce successful offspring during “lemming years.”
It’s still not entirely clear why lemming populations explode every four years, then drop so drastically to the point that the species could actually become extinct. Though weather and winter snow cover probably play a role, researchers have also investigated food supply—lots of lemmings means the Arctic vegetation disappears; when the numbers crash, the vegetation has time to grow back—disease, plus stress and inter-species fighting. The idea that lemmings jump off cliffs, attempting to die, could come from researchers observing restless Norwegian lemmings—forced to expand their territory—jumping onto the ice and into the water during high peak years. (But there’s no real evidence that they were trying to commit suicide. Heck, maybe they just wanted to go swimming.)
One reason why lemmings are so excellent at bringing their numbers back from the brink? They can breed a few weeks after birth. They also stay active all year long. Unlike other rodents, they can’t dig burrows, since a layer of frozen soil (a.k.a. permafrost) covers their entire habitat. No matter: lemmings have short ears, legs, and tails, which helps reduce heat loss in the winter. A heavy layer of snow cover helps them survive. Snow acts as insulation. So, during the cold season, lemmings tend to stick to the “subnivean” zone: the space between the frozen ground and the snow. Not that it’s actually cozy in there (-25°C), but it’s still warmer than the surface of the snow. Good enough for a lemming!