All organisms face attack from many natural enemies and all in turn have some means of defence. Can resistance evolve, and if it can, why doesn't it? Recent work on fruit flies and their parasitic wasps has shed light on these questions. Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land and freshwater zones Drosophila melanogaster (Drosophilidae); Hymenopteran parasites; Asobara & Leptopilina; Host parasite interactions; Palaearctic region; Europe; Interactions with hymenopteran parasites, brief overview Asobara tabida (Braconidae ); Leptopilina boulardi; Leptopilina heterotoma (Cynipidae ); Dipteran hosts; Drosophila melanogaster; Host parasite interactions; Palaearctic region; Europe; Interactions with dipteran host, brief overview none