Lemmings are small, thickset rodents native exclusively to the Arctic tundra, an environment characterized by low temperatures and a short growing season. These mammals are famous for their dramatic, cyclical population swings, which profoundly influence the Arctic food web. Their survival in this northern habitat is directly tied to their specialized diet. Analyzing what lemmings consume helps explain how they manage to thrive in this challenging ecosystem.
The Core Diet: Tundra Vegetation
Lemmings are strict herbivores, with their core diet consisting almost entirely of the low-lying flora that dominates the tundra landscape. During the brief Arctic summer, their primary food sources are nutrient-rich monocots, specifically sedges and grasses. Brown lemmings, for instance, often favor the lower, wetter tundra habitats where these plants are most abundant.
Sedges, such as Carex species, are often the most preferred food item, followed closely by various grasses. Studies have shown that the leaves of these monocots can constitute over three-quarters of a lemming’s diet during the growing season. They exhibit selective grazing behavior, choosing the most palatable and digestible parts of the plants, such as the basal leaf sheaths and tender shoots. Mosses are also consumed, although they are generally less preferred than vascular plants due to lower nutritional value.
Seasonal Changes in Consumption
The lemming diet undergoes a significant transformation as the Arctic summer yields to winter. Unlike many other northern rodents, lemmings do not hibernate, remaining active and foraging year-round beneath the snowpack in the subnivean layer. This requires a shift from surface grazing to accessing subterranean or preserved food.
During winter months, lemmings rely on frozen but still-green plant material found at the base of the snow, along with roots and rhizomes that they can tunnel down to access. Mosses become a more important dietary component in winter, sometimes making up nearly half of the consumption, particularly in drier tundra areas. When fresh green matter is scarce, they consume lichens and the bark and twigs of dwarf shrubs like willow and birch, which offer fallback nutrition.
Foraging Behavior and Habitat
A lemming’s foraging behavior is linked to its need for constant consumption, driven by a high metabolic rate required to maintain body temperature. They are grazers, clipping plants close to the ground as they move through their habitat. This continuous feeding activity means they are rarely far from a food source.
They construct extensive tunnel and runway systems, which are used both for travel and to access food beneath the snow and soil. Brown lemmings tend to prefer moist, low-lying meadows and bogs, which naturally contain a denser concentration of the sedges and grasses they favor. In contrast, species like the collared lemming often inhabit drier, rockier tundra ridges where they forage on different plant species, including willow buds and shrubs. Their ability to tunnel through snow and soil allows them to exploit these different vegetation zones year-round.
Diet’s Role in the Tundra Ecosystem
The lemming’s specialized diet and intense grazing pressure have a direct effect on the structure of the tundra ecosystem. During periods of population peak, their consumption of sedges and grasses can be so extensive that it fundamentally alters the local composition of vegetation. This intense grazing can promote the growth of less-favored plant species while reducing the cover of their preferred food.
As a primary consumer, the lemming acts as a crucial link, transferring energy from the tundra plants to higher trophic levels. The dramatic fluctuations in lemming numbers directly dictate the breeding success and population health of their main predators, including the snowy owl, arctic fox, and ermine. The availability of lemmings as a food source in a given year is a primary driver of predator dynamics across the Arctic food web.