The dwarf shrew (Sorex nanus) is one of the smallest mammals in the world, and inhabits a variety of habitats in western North America. Very little is known about this shrew, and relatively few specimens have been collected. Like most members of Soricidae, the dwarf shrew has a long and pointed nose, small eyes and ears, and a small body. It is difficult to distinguish from other shrews and generally has to be identified by dental characteristics. The dwarf shrew occurs primarily in mountainous areas, apparently preferring rock outcrops and talus slopes in alpine, subalpine, and montane settings. However, it has been occasionally found in lower and more arid environments such as shortgrass prairie, shrub-steppe, and stubble fields. Dwarf shrews are active throughout the year and feed primarily on insects, soft-bodied spiders, and other small invertebrates. The dwarf shrew nests in underground burrows and usually breeds in late June to early July. First litters of 6-7 young are born in late July to early August, with second litters following in late August and early September. The population status and trends of the dwarf shrew are not well known; it is generally regarded as a rare species, but this may be an artifact of under-sampling and the overall difficulty of detecting such a small and cryptic species.
