A small rodent (family Cricetidae), 7–15 cm long, with a short tail and long, soft fur, found throughout northern hemisphere tundra regions. They are mainly herbivorous, solitary, and remain active through the winter, tunnelling beneath the snow and subsisting on grasses they stored earlier. Their populations fluctuate and at times of high population density some species migrate, sometimes drowning while swimming across water bodies that prove too wide for them. There are many species.