The Gasteruptiidae are one of the more distinctive families among the apocritan wasps, with surprisingly little variation in appearance for a group that contains around 500 species in two subfamilies (Gasteruptiinae and Hyptiogastrinae) and with 9 genera worldwide. The propleura form an elongated "neck", the petiole attaches very high on the propodeum, and the hind tibiae are swollen and club-like. The females commonly have long ovipositor (except in the genus Pseudofoenus), and lay eggs in the nests of solitary bees and wasps, where their larvae prey upon the host eggs, larvae and provisions.