Fate of bacteria ingested by larvae of the freshwater mayfly,Ephemera danica

The fate of bacteria in the food of a common freshwater invertebrate has been studied both in controlled laboratory experiments and in a stream sediment. The animal chosen was the larva of the burrowing mayfly,Ephemera danica. It ingested all available bacteria nonselectively. More bacteria were found associated with the hindgut than with the mesenteron despite continuous plug flow of food through the alimentary canal. Species of bacteria were affected in different ways.Aeromonas hydrophila andCitrobacter freundii were both digested, the former selectively.Flavobacterium sp. and other unidentified species appeared to attach to the hindgut wall. Digestion of bacteria was not due to a sudden change in pH.