Big brown bats (Eptesicus fuscus) from a colony in Delaware County, Indiana were captured weekly from 9 July to 13 September, 1993. Food habits of the bats were quantified by analysis of fecal pellets collected in the field. The major foods were Coleopterans, particularly carabids and the agricultural pest Diabrotica undecimpunctata (averaging 54.47% and 32.91% of the total volume of fecal pellets, respectively). Other foods included Acrosternum hilare, Lepidoptera, Cicadellidae, Scarabaeidae, Curculionidae, Chrysomeloidea, Dytiscidae, Lygaeidae, Hemerobiidae, Gryllidae, Miridae, and Delphacidae. The volume of Carabidae and Galerucinae and the frequency of Carabidae and Scarabaeidae in fecal pellets varied temporally. Adults and juveniles differed significantly in the volume of Carabidae in the diet late in the summer. There was no significant difference in diet between the sexes. Diet of adults was more diverse than that of juveniles. Juveniles of both sexes had similar diet diversity. / Department of Biology