Honey bee,Apis melliferaL., drones and workers were used to examine how differences in morphology, physiology, and behavior affect heat exchange and thorax temperature (Tth) during flight. Drones had twice the body mass (Mb) of workers (199.4 ± 2.5 versus 101.8 ± 3:3 mg) and exhibitedTth>2°C higher. Drones were unable to lowerTththrough regurgitation or through shunting heat to the abdomen. Heat production during hovering increased withMbwhereas total heat loss increased withMband with flight speed (V). Despite their larger size and higherTth, drones flew slower than workers. A heat budget model predicted thatTthwould decrease sharply withV, increase with body mass, and increase with the ratio of thorax mass to body mass. The model closely predicted theTthdifference between drones and workers and demonstrated that the higherTthof drones is primarily (75%) an effect of largeMh, somewhat (15%) a result of the high ratio of thorax to body mass and, to a lesser degree (10%), a result of slowerV. These morphological and behavioral traits are sufficient to account for the difference inTthbetween drones and workers.