Avoiding competition is thought to explain insect successional patterns on carrion, but few studies have looked at competition directly. We use replacement series experiments with three species of blow flies: Phormia regina (Meigen) (Diptera: Calliphoridae), Lucilia sericata (Meigen) (Diptera:Calliphoridae), and Chrysomya rufifacies (Macquart) (Diptera:Calliphoridae) to characterize competitive relationships. From experimental results, P. regina showed a significant competitive advantage over L. sericata. Infestation of carrion differs between L. sericata and P. regina; specifically, L. sericata oviposits on carrion without any delay, while P. regina typically delays oviposition. Our findings are consistent with the notion that differences in oviposition times represent a mechanism for L. sericata to avoid potential competition. Competition by C. rufifacies differs since C. rufifacies, in the event of a limited food supply, will prey on other maggot species. In replacement series experiments, C. rufifacies killed all P. regina in mixed treatments, representing an ultimate competitive advantage. In the United States, these two species do not often overlap because of differences in seasonal distribution. However, with climate change, phenological separation may grow less distinct. Surprisingly, in replacement series experiments with C. rufifacies and L. sericata, no competitive interactions were observed. In other studies, L. sericata has been shown to form clusters away from predaceous maggots, allowing improved survival, which may account for the absence of predation by C. rufifacies. Finally, this study shows that replacement series models are useful in measuring competition, supporting the notion that interspecific competition between necrophagous insect species may have driven life history traits of those species.