The crops and guts of adults of Leptohylemyia coarctata (Fall.) from different parts of England and Scotland contained spores of Septomyxa affinis. This fungus is widespread on dead wheat leaves and grass in wheat fields and is an important food for the flies, especially in south and east England during July and August. Of all flies dissected in 1967, 1968 and 1969, 57%, 39% and 45%, respectively, contained Septomyxa spores. Spores of other fungi, pollen grains, bacteria and yeasts were also ingested. All solid food was ingested in water or honeydew. The weight of the newly emerged female fly almost doubled with the ripening of the first batch of eggs, whereas males remained the same weight or became lighter. Different individuals had different numbers of ovarioles, so the number of eggs ripe and ready to lay at the same time also differed between individuals. The mean numbers, 25·6 ± 0·8 in 1968 and 28·6 ± 0·4 in 1969 were fewer than the usually accepted 32. During August, before all the eggs had been laid, many flies were killed by Entomophthora muscae and Strongwellsea castrans.