In closely related tenebrionid beetles (tribe Adesmiini) in the Namib Desert, locomotion speeds and body temperatures are correlated with the ecology of different species. We measured average running speeds of 90 cm/s for Onymscris plana, 23 cm/s for Physsdesmia globosa and 3 cm/s for Epiphysa arenicols. The speed achieved by O. plana is probably the highest yet recorded for any pedestrian insect. Relative speeds of the three tenebrionids are related to leg length and muscle mass, and to behavioural thermoregulation. The beetles are flightless and ectothermic, and exercise does not elevate their body temperature. Keywords: Body temperature, Ecological correlates, Flightless tenebrionid beetles, Locomotion speed, Morphometries, Namib Desert, Tenebrionid beetles.