Non-native species that become invasive can significantly alter the environment. For example, a recent study showed that Potamopyrgus antipodarum, a freshwater snail from New Zealand, consumed 75% of gross primary productivity in a stream in the GreaterYellowstone Ecosytem. Such a high rate of consumption suggests that P. antipodarum are likely to have significant ecological and evolutionary effects on native grazers. To determine the extent of dietary overlap between P. antipodarum and native grazers, we examined periphyton that remained after two weeks of grazing by the invasive snail and three native species; the mayfly Ephemerella and caddisfly Glossosoma that primarily graze periphyton, and the caddisfly Brachycentrus, which is a facultative grazer. After Glossosoma were omitted from the analyses because of mass mortality, we found that only the invaders and mayflies significantly reduced chlorophyll a and ash free dry mass relative to ungrazed controls. The invasive snail also had the largest effect on the community of diatoms. Relative abundance of diatoms were similar among grazers suggesting that significant overlap exists in the diets of the invasive and native grazers. These results suggest that the invasive snail is likely competing with native grazers for food resources.