Water loss and cuticular lipid composition were examined in two species of tenebrionid beetles from the Namib Desert. Onymacris plana, a large diurnal species, exhibited significantly lower water loss rates (mg g-I h-I) 30°C, 35°C and 40°C than the smaller, nocturnal Lepidochora discoidalis. Rates for both species were lower than those oj most desert insects.