The absence of predators is often invoked to explain the ability of non-native species to successfully invade a habitat, however native species can control or regulate populations of invasive species through predation. To better understand the regulation of invasive Gambusia affinis (Western Mosquitofish), we conducted a laboratory experiment to examine the potential for native Cambarus thomai (Little Brown Mudbug) and adult conspecifics to consume Western Mosquitofish fry. On average, female Western Mosquitofish consumed nearly 3 times the number of fry in 24 h than males. Little Brown Mudbug, consumed some of the Western Mosquitofish fry, but the resulting mosquitofish mortality was not significantly higher than the control (which had 100% survivorship). Our results show that cannibalism is a potentially significant source of mortality in Western Mosquitofish, and thus may be a factor involved in the regulation of their population dynamics. However, native Little Brown Mudbug, while they do consume mosquitofish fry, are probably not a major source of mosquitofish mortality in nature.