Body temperature regulation in desert robber flies (Diptera: Asilidae)

We investigated effective thermal environments and behavioural and physiological mechanisms for thermoregulation in two sympatric desert robber flies, Promachus giganteus (Hine) and Efferia texana (Banks). Although similar in body shape and colour, P. giganteus are 4–8 times heavier than E. texana. During midday, operative temperatures near the ground were substantially higher for P. giganteus (56–73°C) than for E. texana (54–63°C). Correspondingly, P. giganteus generally perched at greater heights above the ground than did E. texana. Both species maintained thoracic temperatures between 40 and 45°C during most of the day. However, differences between thoracic and abdominal temperatures for individual flies were significantly lower in P. giganteus than in E. texana. In the laboratory, P. giganteus regulated thoracic temperature by pumping haemolymph into the abdomen. This ability may have accounted for the smaller differences observed between thoracic and abdominal temperatures in P. giganteus and may have allowed this species to search for food and mates during midday when E. texana sought shade.