We examined the diet of big brown bats (Eptesicus fuscus) during an emergence of 17-y cicadas (Magicicada spp.) in May and Jun. of 2004 in Indiana. We collected guano from a maternity colony of big brown bats and compared the diet during the cicada emergence to the diet during the same period of a non-cicada year. In contrast to previous studies, homopterans (predominantly 17-y cicadas) were a common food item (22.9–23.6% volume) during the peak of cicada abundance. Scarabaeidae (13.8–48.5%), Carabidae (7.3–36.9%) and hemipterans (19.4–29.3%) were also common prey items during the cicada emergence. Although periodical cicadas constituted a fair amount of the diet during the emergence, the dietary diversity of big brown bats during the emergence was similar to that of non-cicada years. Our results demonstrate that big brown bats forage on 17-y cicadas during a cicada emergence. However, despite the superabundance of cicadas, big brown bats do not specialize on cicadas to the relative exclusion of other prey types.