The northern bog lemming (Synaptomys borealis) is a small North American lemming. It is one of two species in the genus Synaptomys, the other being the southern bog lemming (S. cooperi). Very little information is available about this species' life as they are hard to find and study. The northern bog lemming is a small, reddish-brown rodent with a short tail, and distinct markings on their upper teeth. These markings, along with having four pairs of teats, distinguishes this species from the southern bog lemming. The northern bog lemming lives in wet habitats in North America and is omnivorous, eating herbaceous material and invertebrates. They are thought to be extremely sociable animals and sexually mature at around 6 weeks old. Predators include most medium to larger sized carnivorous and omnivorous mammals that eat smaller mammals. The northern bog lemming is listed as a species of "Least Concern" by the IUCN Red List and is considered threatened or of concern in states such as Minnesota and Maine.

A common synonym genus that is used to describe northern and southern bog lemmings is the genus Mictomys. Northern bog lemmings are in the subfamily Arvicolinae. The six different genera of lemmings include Dicrostonyx, Lemmus, Eolagurus, Synaptomys, Lagurus, and Myopus. There are currently 20 known species of lemmings.

With no specific sexual dimorphisms, the northern bog lemming has varying shades of brown, reddish-brown, and chestnut fur on the top, with gray to light brown fur on the bottom. Their fur is long and coarse. These lemmings have black beady eyes, a short tail, small ears, grey feet, and a small, flat nose. They are around 4.8 to 5.7 inches (12 to 14 cm) long with a tail that is usually shorter than 1 inch (2.5 cm). They weigh around 1 ounce.

Northern bog lemmings have 16 thin, sharp teeth. They can be distinguished from other rodents by the distinct grooved markings on their top incisors. As they look extremely similar to the southern bog lemming, one can distinguish them by looking at the base of the northern bog lemming's ears for rust-colored fur, something that the southern bog lemming lacks. Northern bog lemming females also have four pairs, or eight individual, nipples while southern bog lemming females only have three pairs.

These animals are found native to wet northern forests, bogs, tundra and meadows in Canada, Alaska, northern Washington, Minnesota, and New England. By the St. Lawrence river in the Appalachian Mountains, a small population of northern bog lemmings can be found as well. Their habitat consists of bogs with Sphagnum, as well as areas with bog like conditions. They are often found living in open areas around wet rocks and fallen logs, wet grassy areas, others mosses, and coniferous forests. At almost all locations where they are found, there is usually some small water source present.

The northern bog lemming is an omnivorous mammal that primarily feeds on grasses, moss and sedge. Occasionally, they will eat insects, worms, slugs, snails, or fungi. A common habit of these lemmings, which signifies their presence in an area, is that they create surface tunnels under vegetation to travel through and to forage in. They line these tunnels with piles of cut grass. They also leave behind green scat.

These lemmings are cathemeral mammals, which means they are active at different times during the day and the night, and they do not hibernate. As they have been observed to be extremely sociable with others of their species, they often form colonies. They also do not move habitat throughout the year and stay in the same home range for the majority of their lives. On top of building their own tunnels under vegetation and under the surface of the ground, northern bog lemmings often shares habitat with other rodents, and will use their tunnels as well. Rodents that northern bog lemming's share habitat with include meadow voles and northern short tailed shrews.

During the spring, summer and fall when there is no snow cover, northern bog lemmings are most active below the earth's surface due to threats of predators. During this time, they live in burrows built underground, under fallen logs, or in sphagnum moss. Northern bog lemmings are active above ground most of the winter season as the risk of coming into contact with predators is lower. In this season, they build their nests between the snow and the ground layer. Their nests are built from the grasses, dried leaves, moss, and sedges they find in their habitat, as well as their own fur, and are spherical in shape.