Adults of Hypoderma bovis (L.) were reared in the laboratory at Kerrville, Texas, from grubs that had dropped from imported cattle. The flies were induced to mate and oviposit by tethered flight, thus infesting calves with four replicates of 50, 100, 200, 500 and 1,000 eggs in April and May. The outdoor behavior of the flies in the mating and oviposition procedures was similar to that observed in Canada, where H. bovis is indigenous. However, air temperatures above 85 to 90°F. curtailed mating and oviposition, which could therefore be induced only in the mornings and evenings. Survival of the larvae to the hypodermal stage was density-related, taking the form Y = 5.07× 280 for egg densities up to 500 per animal, which was a similar relationship to that obtained in Canada. However, there was a markedly lower survival in the late-season 1,000-egg infestations. This was attributed to either infertility or mortality of the eggs because of the excessively high temperatures. It was concluded that climatic factors at Kerrville did not limit the normal survival of the larvae but partly limited the reproductive activity of the adults and affected the viability of the eggs. Reasons for the absence of H. bovis at Kerrville might be determined through studies of the survival and development of puparia under natural conditions.