ABSTRACT
Male rain beetles (Pleocoma; Scarabaeidae) of western North America engage in intense mate-searching activity at night during the winter. They may achieve a temperature excess greater than 35 °C in flight, even though their thoracic pile is ineffective as insulation. Males also maintain thoracic temperature at high levels while walking on the ground in search of females. Female Pleocoma are flightless and are non-endothermic. In the laboratory, males maintained elevated body temperatures for as long as 4·2 h while walking in a respirometer chamber at an ambient temperature of 9°C. Energy metabolism and body temperature during these periods of sustained endothermy oscillated. Walking speed increased exponentially with body temperature. Male rain beetles compete (scramble competition) for opportunities to mate. It is likely that their mating success and ability to avoid predators depend on flight and rapid walking, which in turn depend on their having a high internal temperature.
