The effects of temperature, food type, and sucrose feeding on longevity of house flies,Musca domesticaL., were studied. Longevity decreased with increasing temperature. Flies fed cattle manure, poultry manure, or nothing had similar lifespans, which were lower than lifespans of flies fed milk. Sucrose increased longevity for flies on all diets except milk. Addition of poultry feed to a diet of poultry manure also increased longevity. Variation in longevity was highest for flies that were fed milk or sucrose. The intercept (but not the slope) of the relationship between longevity and temperature was affected by diet, indicating that the overall level of the response of fly longevity to temperature was governed by diet. Sugar feeding was detected in 12% of female flies captured in three dairies, and occurred at similar levels among dairies.