Abstract The vespid hymenopteran, Vespula germanica (Fabr.) regulates its thoracic temperature to around 33° - 38° C in environmental temperatures between 15° and 35° C. Thermal conductance of the thorax of V. germanica was found to increase from 1.6–2 mW/°C in still air to 2.7 mW/°C in air moving at a speed of 3 m/sec. Thus the metabolism needed to maintain the excesses of temperature can be estimated. Although V. germanica lacks a developed coating of hair or other insulating structures, heat loss is relatively limited owing to the body profile. This appears clearly when V. germanica is compared with another vespid, Polistes omissus (Weyr.). In the latter, thermal conductance is greater, particularly in slow moving air, so that heat production is insufficient to control body temperature. Measurements of abdominal temperature of fliyng wasps plus direct observations indicate that heat transfer from thorax to abdomen is insufficient to regulate thoracic temperature when the environmental temperature is hi...