Very small parasitoid wasps. Males winged, wings rarely reduced, females winged, wingless or with reduced wings. Adults usually black. The adults are active from April until October, but mainly during the summer months. They are external parasitoids on beetle or lepidopterous larvae. The host is rapidly paralysed and may be killed. It may be dragged or carried to a concealed place, or may already be in a concealed place, e.g. within rolled leaves or under bark. One or more eggs are laid on the host. The larvae feed externally on the host. The female may stay with the larvae until they mature. Females probably over-winter as adults. Nationally: 9 genera with 14 native species, with a further species restricted to the Channel Islands, and several introduced species associated with granaries and storehouses.