How limited (or not) is the dietary range of an animal species? How does that host specificity plot across major lineages of organisms? How does that affect the structure of ecological communities? These are major questions in ecology, especially for invertebrates, where they have major implications for academic questions, such as how many species of insects there are, and practical applications in fields such as biological control (1). A multidisciplinary team representing field ecology, molecular genetics, and morphological taxonomy presents data in this issue of PNAS (2) that challenge our traditional assumptions of parasite diversity and host specificity in a system of tachinid flies that parasitize moth and butterfly caterpillars in Costa Rica (Fig. 1).