This thesis is an investigation of the practicality of a method to identify insect species from fragments which survive mastication and digestion by bats. The investigation makes use of optical and scanning electron  microscopes in conjunction with a reference collection of insects. Twelve species of Coleoptera were fed to four captive Eptesicus fuscus and a key made using species specific "tags" which survived ingestion and digestion.  The parts of an insect culled by bats in relation to the size and sclerotized nature of that insect and the size of the stool produced by the bat relative to the size of the insect were found to be related. Stomachs of 12 Myotis lucifugus obtained during swarming were examined to test the difference between stomach analysis and feces analysis, and to test the practical value of the above method. Analysis of feces is superior to analysis of  stomach contents as a means of determining the diet of insectivorous bats.