Adults are small to medium-sized (2.5-9.0 mm) flies, relatively stout, usually dark coloured Nematocera with stout legs. They are associated with ancient woodland. Larvae are xylosaprophagous and live in the moist, rotting wood of stumps and fallen trees.
Most are considered endangered due to the vulnerability of their habitat.
There are 15 described species worldwide from New Zealand, North America, South America, Japan and Russia. The 3 species in Europe are suspected to be introductions. There is one know fossil species from the Jurassic.