The Pteromalidae are a very large family of mostly parasitoid wasps, with some 3,450 described species in about 640 genera (the number was greater, but many species and genera have been reduced by synonymy in recent years). The subfamily-level divisions of the family are highly contentious and unstable, and the family thought to be "artificial", composed of numerous, distantly related groups (polyphyletic). Accordingly, details of their life histories range over nearly the entire range possible within the Chalcidoidea, though the majority are (as with most chalcidoids) parasitoids of other insects. They are found throughout the world in virtually all habitats, and many are important as biological control agents. The oldest known fossil is known from the Early Cretaceous