Chrysomya Robineau-Desvoidy blow flies recently introduced to the Americas include two species, Ch. megacephala (Fabr.) and Ch. chloropyga Wiedemann (= Ch. putoria) with purely saprophagous larvae, and two, Ch. albiceps (Wiedemann) and Ch. rufifacies (Macquart), that are facultative predators on other maggots. Patterns of adult abundance suggest that the invading species suppress the saprophagous native Cochliomyia macellaria (Fabr.), and do so more effectively in combination than individually. We hypothesized that Ch. megacephala, historically sympatric with Ch. rufifacies, is relatively resistant to predation by Ch. rufifacies, which could provide it with a competitive advantage over a more vulnerable C. macellaria when larvae of all three occur together. To test this hypothesis, larvae of both prey species were individually paired with larvae of Ch. rufifacies in the laboratory. C. macellaria were consistently killed at a higher rate than were Ch. megacephala.