||There is speculation that the little brown bat ( Myotis lucifugus ) is important in controlling populations of pest insects such as mosquitoes, but the species' diet remains poorly understood. I investigated dietary preference of little brown bats in southeastern Pennsylvania by comparing weekly guano samples from two maternity roosts against concurrent insect sampling using sticky traps across 12 weeks in summer, 2005. Bats had similar, selective diets at both sites, despite differences in prey availability. Diptera, but not mosquitoes, were overrepresented in guano samples; available insects eaten rarely included Hymenoptera and Psocoptera. Little brown bats do not appear to feed selectively on mosquitoes, and are thus unlikely to be exposed to West Nile Virus through ingestion, but these bats may have impacts on populations of other pest insects. Similar methods could be used to advance understanding of the resource requirements and foraging ecology of the endangered Indian bat ( M. sodalis ).