The snow lemming, primarily the Collared Lemming (Dicrostonyx species), is a small rodent adapted to the extreme Arctic tundra. As a primary consumer, it feeds on vegetation year-round. Its high abundance makes it a concentrated food source, transferring energy from tundra plants to a wide range of avian and mammalian predators. The biology of the snow lemming is finely tuned to its frigid home, allowing it to remain active throughout the long, dark winter months.
Physical Characteristics and Arctic Adaptations
The snow lemming survives temperatures far below freezing through physical and behavioral adaptations. Like other Arctic mammals, it features a compact, rounded body with reduced extremities—short ears, a stubby tail, and small legs—to minimize surface area for heat loss. A thick, dense coat of fur provides insulation, helping to maintain a stable body temperature.
The Collared Lemming’s coat transforms seasonally from mottled gray-brown in summer to pure white in winter. This camouflage, triggered by changing daylight hours, offers protection from predators against the snowy backdrop. Accompanying this molt, the claws on the third and fourth digits of the forefeet become enlarged and bifurcated. These specialized, shovel-like claws are used for digging through hard-packed snow and ice. They help construct and navigate the subnivean space, an insulated layer between the ground and the snowpack.
A snowpack deeper than 20 centimeters is preferred, as this thickness creates a stable microclimate with temperatures near or just below freezing, significantly warmer than the air above. Within this network of tunnels, the lemming builds nests of shredded grasses and sedges, where it can rest, forage, and reproduce throughout the winter.
Geographic Range and Diet
The snow lemming is distributed across the circumpolar Arctic, inhabiting the treeless tundra regions of North America, Greenland, and Eurasia. It typically favors dry, elevated terrain in the summer, where deep burrows can be excavated above the permafrost layer. However, the requirement for a stable subnivean space in winter often draws lemmings to microhabitats where snow accumulates deeply, such as gullies or riparian areas.
As an herbivore, the lemming’s diet shifts seasonally, but it remains active and feeds continuously. In summer, it consumes grasses, sedges, and berries. During winter, the lemming relies on vegetation accessible from its subnivean tunnels, primarily feeding on the roots, stems, willow buds, and bark of dwarf shrubs. It locates this buried forage using its highly developed sense of smell, tunneling through the soft basal snow layer known as depth hoar to reach the plants at ground level.
Understanding Lemming Population Cycles
The “boom-and-bust” population cycle typically occurs every three to five years across the Arctic. During a peak phase, lemming density can soar, sometimes increasing their numbers by a hundredfold in local areas. This exponential growth is fueled by successful winter reproduction within the protective subnivean environment, allowing them to raise multiple litters shielded from predators and severe weather.
The population crash that follows a peak is driven by a complex interplay of factors, including the density of predators, food scarcity, and winter weather. Specialist predators like the ermine, whose population often lags behind that of the lemming, exert intense pressure, particularly when lemmings are forced to move outside the safety of their tunnels. Furthermore, climate change-related events, such as mid-winter rain-on-snow, can create impenetrable ice layers that collapse the subnivean space and cut off access to food, leading to mass mortality and a rapid decline in numbers.
These population movements, driven by a surplus of lemmings attempting to disperse and find new territory, are the origin of the persistent mass suicide myth. This misconception, popularized by a fabricated film scene, inaccurately suggests a deliberate self-destruction. In reality, the lemmings are simply migrating due to resource depletion. Any deaths are accidental, resulting from drowning while attempting to cross rivers or from predation in unfamiliar areas.