The Nemouridae are a family of stoneflies containing more than 600 described species, occurring primarily in the Holarctic region. Members of this family are commonly known as spring stoneflies or brown stoneflies. Fly fishermen often refer to these insects as tiny winter blacks. Although these insects use a wide range of flowing-water habitats, they tend to be most prevalent in smaller streams. The nymphs are distinctive, being broad-bodied and bristly with divergent wing pads.