Northern bog lemming (Synaptomys borealis)

Physical description

The northern bog lemming has a small, circular body covered with long, gray or brown fur and pale gray belly. Taxonomic note: Three described subspecies occur in Washington: S. b. truei is found west of the Cascades, S. b. chapmani occurs in northeastern Washington, and S. b. artemisiae occurs in between. The taxonomic validity of S. b. artemisiae may need re-evaluation.

Ecology and life history

Northern bog lemmings typically inhabit sphagnum bogs and fens, wet meadows, moist mixed and coniferous forests, alpine sedge meadows, krummholtz, spruce-fir forest with dense herbaceous and mossy understory, and mossy stream sides. S. b. artemisiae was thought to be associated with sagebrush, but recent records suggest it is more often found in typical mossy habitats.

Northern bog lemmings primarily eat grasses and sedges, but also eat fungus, mosses, snails, slugs, and other invertebrates. In summer, they clip vegetation and create runway systems through the underbrush where they forage.

They nest underground during summer, and in winter construct spherical nests of mosses, grasses, and sedges on the ground surface under the snow. Underground burrow systems may be up to one foot deep.

The breeding season lasts from May through late August, and litter size ranges from two to eight young, and females may have two to three litters in a breeding season.

Geographic range

This species is found only in subarctic climates from the northern tree line south into Washington, Idaho, Montana, Minnesota, and New England. The Washington watersheds that contain known records include the Lower Pend Oreille, Middle Pend Oreille, Upper Methow, Lost River, Upper Chewuch, and Sinlahekin Creek. The population status for each of the three subspecies in Washington is unknown, but the species is considered rare throughout its range.