The total length of the least shrew is from three to 3 ½ inches. Its tail length ranges from ½ to ¾ inches, which is the shortest tail of all Pennsylvania shrews. The only other species of shrew with a short tail, the more common northern short-tailed shrew, is larger (total length is four to five inches) and is dark slate-gray in color. Shrews are insectivores, meaning they feed on insects and lots of them. For their size, shrews are some of the most voracious and ferocious predators of the animal kingdom, eating their body weight or greater in food daily.

The least shrew prefers grassy open lands, along edges of openings, and may be also found in open forests and marsh habitats. It is active year-round, mostly during evening hours. It commonly forages for food in runways created by meadow voles, but also constructs its own narrow passageways within vegetation for foraging and dispersal. Least shrews feed primarily on insects and their larva, earthworms, spiders and sometimes snails. It occasionally exhibits hoarding behavior, unusual among shrews. It is sometimes referred to as the "bee mole" because it has been found to infrequently enter bee hives and feed on the brood.