A survey of indigenous parasitoids attackingMusca domesticaL. andStomoxys calcitrans(L.) pupae was conducted for 2 yr at eight dairies by exposing weekly samples of laboratory-reared fly pupae (sentinel bags). Mean relative abundance of each species was 59%Muscidifurax raptorGirault and Sanders, 14%Urolepis rufipes(Ashmead), 11%Phygadeuon fumatorGravenhorst, 10%Spalangia cameroniPerkins, 3%Spalangia nigroaeneaCurtis, and 2%Trichomalopsis dubius(Ashmead). Rare species includedPachycrepmdeus vindemmiae(Rondani),Nasonia vitripennis(Walker),Dibrachys cavus(Walker),Spalangia nigraLatreille, andMacroneura vesicularis(Retzius). Total parasitism was phenologically synchronized with the house fly population occurring between 17 May and 27 October, but it peaked 1–2 mo after the fly population peaked.M. raptor, U. rufipes, andP. fumatorwere common in June. A decrease in parasitism byM. raptorandU. rufipesduring late July may represent a gap between the first two generations. Paired samples of sentinel house fly and stable fly pupae indicated no difference in parasitism byM. raptoror by all species combined. However,U. rufipesparasitized more house fly pupae, andP. fumatorparasitized more stable fly pupae.