The principal hosts of G. claripennis on the Continent are the larvae of the tortricid moths Sparganothis pilleriana (Denis & Schiffermüller) and Eupoecilia ambiguella (Hübner) (Richards, 1939). In Britain, both these moths are found locally in a narrow southern strip, S. pilleriana being subcoastal. Goniozus has been reared from larvae of the lepidopterous families Choreutidae, Gelechiidae, Oecophoridae and Tortricidae (Hansen, 1995). The biology of G. claripennis has been described by Voukassovitch (1924). When stinging a caterpillar, the female climbs onto its back and palpates it before stinging. She often then imbibes the body fluids from the punctures. Between one and eight eggs are laid externally on host larvae that are 6 to 20 ram in length. Two females kept in captivity laid 36 and 77 eggs, and lived 25 and 40 days respectively. At temperatures of 18-20 °C, the period from egg to adult was 36 days. Unfertilised eggs gave rise to male wasps which emerged and then mated with females inside their cocoons.