Two stable fly species, Stomoxys calcitrans (L., 1758) and Stomoxys niger niger Macquart, 1851, co-occur in La Réunion, where they are important pests of cattle. The survival and developmental rate of the immature stages were compared at five constant temperatures from 15 to 35°C. In both species, immature survival was highest at 20–25°C and markedly decreased at 15 and 35°C. At the lower temperatures, mortality was observed mainly for S. calcitrans larvae and S. niger eggs. At the higher temperatures, mainly pupae of both species died. At all temperatures, S. calcitrans survived better than S. niger. Developmental time was highly similar in both species, decreasing from 71 d at 15°C to 13 d at 30°C in S. calcitrans and from 69 d at 15°C to 14 d at 30°C in S. niger. Developmental times increased slightly at 35°C. Surprisingly, the tropical S. niger developed slightly faster than the cosmopolitan S. calcitrans at 15–20°C; the reverse was found at higher temperatures. Temperature summation models confirmed that S. niger had a lower developmental threshold than S. calcitrans (11.3 versus 12.2°C) and higher day-degree (DD) requirements to complete development (251 versus 225 DD). Overall, the results suggest that S. calcitrans is better adapted than S. niger, in terms of adult production from eggs, in the temperature range of La Réunion.