Fanniids are a small family of flies that are known mainly because many of the species are associated with humans and are of medical and forensic importance. Most of the species of Fanniidae have been described from the Holarctic region, but recently many new species have been described from the Neotropical region. The Fanniidae are inhabitants of forested areas, and are relatively rare in open landscapes. Males of almost all species form swarms in shaded areas and females may be attracted to decaying organic matter and excrement. Fanniidae can be most readily distinguished from other calyptrate flies found in New Zealand by the shape of the subcostal vein, which runs straight in its apical half, without any sinuous bend.