Abstract 1. Oxygen consumption in five sympatric species of Chihuahuan desert ants was measured at three relative humidities at 15, 25 and 35°C. 2. The rate of oxygen consumption ( QO 2) exhibited non-linear increase in Formica perpilosa, Pogonomyrex desertorum, Novomessor cockerelli and Trachymyrmex smithi neomexicanus, but was linear in Pogonomyrmex californicus. 3. Vapor pressure deficit had a significant effect on QO 2 of P. desertorum, T. s. neomexicanus and F. perpilosa but not on the other two species. 4. Activity increased at higher vapor pressure deficits in P. desertorum, N. cockerelli and T. s. neomexicanus. 5. The highest vapor pressure deficits at 35°C resulted in deaths of all species except P. californicus and T. s. neomexicanus died at intermediate and high vapor pressure deficits at all temperatures.