Wood lemmings are greyish-black on the upperparts with a rust-brown area on the back; the undersides are somewhat lighter. Wood lemmings are 6.5–11.5 cm long, the tail measures 0.9–1.8 cm, and the animal weighs 10–45 g. Wood lemmings are found in moorland and damp conifer forest (particularly spruce) with thick moss. They feed mainly on moss and lichens, but also eat grass, reeds and horsetails. Their tracks resemble those of other voles, especially those of Norway lemming. The scat can be light green when really fresh, about 8 mm long; older scat is yellowish brown. Wood lemmings are nocturnal and active year-round. Wood lemmings also experience population booms and at these times will wander far and wide. Their tunnels in the moss may be clearly visible. Wood lemmings eat the top layer of moss, and these grazed areas then stand out as lighter spots in the landscape.