Breeding experiments of caterpillars were performed to assess the development and biology of the critically-endangered butterfly species, Coenonympha oedippus (Fabricius, 1787), during its larval stages. Pseudoarrhenatherum longifolium (Pocaceae), a grass commonly found in South western France, can serve as a feeding plant for caterpillars of C. oedippus. However, and in contrast to the literature, caterpillars did not feed on the Black Bogrush Schoenus nigricans (Cyperaceae). Furthermore, for the first time a parasitoid of C. oedippus is described, the braconid wasp Diolcogaster abdominalis (Nees, 1834). none