In Germany, the Geoffroy's bat (Myotis emarginatus) is one of the rarest bat species. In south-western Germany (federal state of Baden-Württemberg), only four nursery roosts of M. emarginatus are known. Referring to the trophic niche of this species and to own observations, we hypothezied that cowsheds are important foraging areas for M. emarginatus in Central Europe. This would have important implications for the conservation of this species. To test this hypothesis we conducted a diet analysis aiming at three major aspects: the trophic niche, indications for foraging habitats used, and the importance of these foraging habitats throughout the nursery season. Flies (Brachycera) made up the largest volume in the diet of M. emarginatus throughout the season, followed by spiders (Araneida) and butterflies (Lepidoptera). Among the flies, the genus Musca and the species Stomoxys calcitrans were found in more than half of the investigated faecal pellets. Both of these fly-taxa are strongly related to cattle farming. Therefore we conclude that the individuals of the investigated colony of M. emarginatus were mainly hunting in the vicinity of cattle farms during the whole nursery season. Consequently, the preservation of traditional cattle farming is likely to play a key role for the conservation of M. emarginatus in Central Europe.