Myopus schisticolor
wood lemming

Myopus schisticolor populates the taiga (Niethammer, 1990). It also occupies areas of the coniferous forest zone from Norway to eastern Siberia, as well as areas of northern Mongolia (Nowak 1999). It is especially abundant in many areas of central Sweden (Fredga et. al., 1998), Finland (Eskelinen, 1997) and Russia (Amori, 2001).

M. schisticolor lives in the moss layer on the floor of wet nordic coniferous woodlands (Niethammer, 1990). It may sometimes also be found living under the roots of trees and beneath fallen tree trunks (Nowak, 1999). In general, it is restricted to the forests (Fredga et. al., 1998).

The Wood lemming is ash-gray with a cinnamon-colored saddle. Due to its similarity in molar pattern to the Norway lemming, systematists have often assigned the Wood lemmings to the genus Lemmus. However, the Wood lemming has distinctively less hair on the soles of its feet and a wide thumb claw that distinguishes it from the Norway lemming (Niethammer, 1990).

Wood lemmings have a soft pelage, dense and slaty black above with a definite reddish brown area on the contour of the back extending from the shoulders to within 15mm of the base of the tail (Nowak, 1999). The rest of the coat is slightly paler on the ventral surface. The peculiar metallic luster on the upper parts is produced by silvery tips on the shorter hairs, with an indistinct showing of black guard hairs. The tail is heavily furred. The palms are naked. The hind feet are densely haired behind the pads but are naked in front of the pads, like the palms of the forefeet (Nowak, 1999). There is no substantial difference in the coloration of the sexes, nor is there much seasonal variation in color. The winter coat is slightly longer than the summer pelage (Nowak, 1999).

Wood lemmings are stout rodents with small ears that project little beyond the fur but which are well developed, rounded and well haired. Valves in the ears regulate the size of the ear openings (Nowak, 1999). The thumb of the hand is small but bears a large, flattened nail with parallel sides and a notch at the end. In this respect Wood lemmings somewhat resemble Lemmus, but are smaller (Nowak, 1999).

(Niethammer, 1990)

High population densities may occur (Niethammer, 1990), and locally limited migrations are known as well (Eskelinen, 1997).

Male home ranges are consistently larger than female. On average, males move distances 4-12 times further than females (Andreassen et. al., 1991).

M. schisticolor gnaw tunnels in moss cushions, feeding mainly on these mosses (Niethammer, 1990). In autumn, they collect and store many moss piles in the spruce forests they occupy in various parts of Finland. They hide their stores under stones, tree trunks and other areas where it is sheltered from the rain. Sometimes stores are kept in open places, such as under growing trees, but this is rare. The areas where they collected mosses are clearly distinguishable from feeding areas. In feeding areas only the tips of the mosses were taken, while in collecting patches the mosses were taken whole. The stores are generally eaten during that following winter. Stores are thought to be especially important during the early winter; 50% of them are consumed completely (Sulkava et. al., 1996).

Wood lemmings have a high metabolic rate, typical of rodents living in high latitudes (Saarela et. al., 1993).

Foods eaten include: mosses, rushes, grasses, sedges (Niethammer, 1990). Specifically, stems of red wortleberry, and the bark of juniper (Nowak, 1999).

Wood lemmings have numerous predators including owls and buzzards (Niethammer, 1990).

Myopus is likely to be seen only in years when its populations become unusually large (Nowak, 1999). Because it is dependent on a relatively narrow set of ecological conditions that are easily disrupted by human activities, it is designated on the "red list" as Lower Risk - near threatened by the IUCN (Nowak, 1999).

Much of the studies done on Wood lemmings have focused on their sex chromosomes. Sex determination in the Siberian Wood lemming has shown there exists an female-biased sex ratio among the lemmings. This sex-bias is the result of a high concentration of the X-chromosome. The X-chromosome in this case induces, in excess, the development of XY females (Gileva et. al., 1991). Their populations have only 20% males, both in captivity and in the wild. Some females have one X-chromosome and one Y-chromosome in each of their body cells, like males of other species. To further this sex bias among Wood lemmings, the XY females develop egg cells with XX-chromosomes in their ovaries. The X-chromosome of the females also differs from the X-chromosome found in the males; there is a female-determining and a male-determining X-chromosome. Possibly this is the means by which the Wood lemming increases its birth rate. Because one male can mate with several females the propagation of these animals may be most successfully accomplished by increasing the number of females in the population (Niethammer, 1990).