In contrast to the Negev Desert, many Namib tenebrionid beetles are diurnal during the summer months. The aim of this study was to investigate the respiratory patterns and metabolic rates of the Negev Desert tenebrionid beetles and to compare them with those of the Namib Desert tenebrionid beetles. This will help to explain what physiological adaptations enable some species to be active during the day and cause others to adjust their activity to prevent dessication. Seely and Mitchell (1987) and Krasnov and Ayal (1995) have suggested that the activity patterns of tenebrionid beetles are influenced by factors, e.g. physiological and reproductive adaptations, other than simple avoidance of high temperatures. Keywords: discontinuous gas-exchange cycle, diel activity, Habitat association, Tenebrionidae, desert.