Norway lemmings (Lemmus lemmus) aren’t always easy to spot until the population booms. In some years, they race through grass, dart between rocks, and even appear in campsites across the Scandinavian mountains. In one peak year, 1974, researchers recorded 22 nesting snowy owls in a single area, each surrounded by piles of lemmings brought to feed their chicks. Hikers reported waves of lemmings rushing across the tundra, and campers described hearing them outside their tents at night.

They are not your average rodent. While most small mammals rely on freezing or fleeing, this species does the opposite. When threatened, it stands its ground, chatters loudly, and may even lunge or bite. Its coat has bold patches of orange, black, and white that stand out against the snow. Biologists believe this vivid coloring, combined with its sharp vocalizations, helps deter certain predators. Even birds like the long-tailed skua have been startled by the aggressive response of a lemming that refuses to back down. Among small rodents, this kind of defiance is rare.