Rates of house fly,Musca domesticaL., destruction byCarcinops pumilio(Erichson) adults andMacrocheles muscaedomesticae(Scopoli) females at two densities in a poultry manure substrate were determined at 27°C as a function of prey availability, and models based on the disk equation of Holling fit the observed data closely (R2>0.92). Asymptotic predation rates were 54 fly immatures destroyed per predator per day forC. pumilioand 17 and 11 forM. muscaedomesticaeat 5 and 20 mites per assay container, respectively. At 15 and 33°C, predation rates ofC. pumiliowere 12.3 and 82.7 per day, respectively, and those ofM. muscaedomesticaewere 5.0 and 36.3 per day, respectively.C. pumiliodestroyed significantly fewer house flies when acarid mites (Caloglyphussp.) were present as an alternative prey than when only fly immatures were present; there were no reductions in predation on the house fly in the presence of nematodes (Diplogasteroidessp.) or sphaerocerid (Coproica hirtulaRondani) immatures.M. muscaedomesticaedestroyed significantly fewer house flies when nematodes and sphaerocerids were present than when only fly immatures were present; there was no reduction in predation on the house fly in the presence of acarid mites.