Urolepis rufipes(Ashmead), previously unreported to parasitize house flies (Musca domesticaL.), was recovered from house fly pupae at five of eight dairies surveyed in 1982 and at all eight dairies surveyed in 1983 in New York State. It was not collected from 8 dairies surveyed in 1981 nor from 10 poultry facilities surveyed in 1981 and 1982. Of the 445U. rufipescollected in 1983, 87% came from outdoors, primarily from manure pits and other accumulations of wet manure.U. rufipeswas collected from July through October, with peak numbers occurring in mid-September. It made up 20% and 15% of all parasitoids collected in 1982 and 1983, respectively. Laboratory studies at 30°C and 60% RH indicate a sex ratio of 2.65 females per male, a mean fecundity of 24.5 (range, 23 to 25) females and 9.2 (range, 3 to 15) males per female, and mean developmental times of 10.2 (range, 9 to 13) and 9.7 (range, 8 to 15) days for females and males, respectively. The short developmental time, the prevalence in wet, outdoor manure habitats, and occurrence at 43°N latitude suggest thatU. rufipesis adapted to flies at dairies in temperate climates.