Encyrtidae

Some species exhibit a remarkable developmental phenomenon called "polyembryony", in which a single egg multiplies clonally in the host and produces large numbers of identical adult wasps. Even more remarkably, some of the larvae are larger than the others and act in a similar way to the "soldiers" of eusocial insects, attacking any other wasp larvae already in the body of the host, and dying without reproducing ("altruism").

Wasps in this family are relatively easy to separate from other Chalcidoidea by features of the wing venation, the migration of the cerci forwards on the metasoma (and accompanying distortion of the tergites), and a greatly enlarged mesopleuron with anteriorly positioned mesocoxae.

An extinct genus Archencyrtus has been described from the Middle Eocene age Sakhalin amber in Eastern Russia.