| classification | lemmings' |
|---|---|
| Domain | Eukaryota |
| Kingdom | Animalia |
| Phylum | Chordata |
| Class | Mammalia |
| Order | Rodentia |
| Family | Cricetidae |
| Genus | Lemmus |
| Species | Lemmus |
source: Wikipedia
Lemmings measure around 13–18 cm (5–7 in) in length and weigh around 23–34 g (0.8–1.2 oz). Lemmings are quite rounded in shape, with brown and black, long, soft fur. They have a very short tail, a stubby, hairy snout, short legs, and small ears. They have a flattened claw on the first digit of their front feet, which helps them to dig in the snow. They are herbivorous, feeding mostly on mosses and grasses. They also forage through the snow surface to find berries, leaves, shoots, roots, bulbs, and lichens. Lemmings choose their preferred dietary vegetation disproportionately to its occurrence in their habitat. They digest grasses and sedges less effectively than related voles. Like other rodents, they have incisors that grow continuously, allowing them to feed on much tougher forage. Lemmings do not hibernate through the harsh northern winter. They remain active, finding food by burrowing through the snow. These rodents live in large tunnel systems beneath the snow in winter, which protect them from predators. Their burrows have rest areas, toilet areas, and nesting rooms. They make nests out of grasses, feathers, and muskox wool (qiviut). In the spring, they move to higher ground, where they live on mountain heaths or in forests, continuously breeding before returning in autumn to the tundra.
Like many other rodents, lemmings have periodic population booms and then disperse in all directions, seeking food and shelter their natural habitats cannot provide. The Norway lemming and brown lemming are two of the few vertebrates which reproduce so quickly that their population fluctuations are chaotic, rather than following linear growth to a carrying capacity or regular oscillations. Why lemming populations fluctuate with such great variance roughly every four years, before numbers drop to near extinction, is not known. Lemming behaviour and appearance are markedly different from those of other rodents, which are inconspicuously coloured and try to conceal themselves from their predators. Lemmings, by contrast, are conspicuously coloured and behave aggressively toward predators and even human observers. The lemming defence system is thought to be based on aposematism (warning display). Fluctuations in the lemming population affect the behaviour of predators, and may fuel irruptions of birds of prey such as snowy owls to areas further south. For many years, the population of lemmings was believed to change with the population cycle, but now some evidence suggests their predators' populations, particularly those of the stoat, may be more closely involved in changing the lemming population.