Heat Loss and the Body Temperatures of Flying Insects

Abstract

1. Comparative measurements of body temperatures and water loss in Schistocerca gregaria showed that evaporation dissipates relatively little of the heat generated by the wing muscles during flight. 2. In perfectly dry air at 30° C, evaporation reduces the temperature excess of the pterothorax by less than 10%, or about 0.5° C. Even at 40° C, which is the highest temperature that will permit continuing flight, the reduction is only about 20%, or 1.2° C, in dry air. 3. A flying locust has no special mechanism, except cessation of flight, to protect it from overheating. Breathing is not markedly increased at high temperatures, nor is the rate of heat production reduced. 4. Very little heat is dissipated from the pterothorax by evaporation through the cuticle. The cuticle becomes permeable enough to allow substantial cooling only at temperatures well above the highest that permit flight. 5. Temperature measurements in Triphaena pronuba and Bombus lapidarius supported the idea that evaporative cooling during flight is not much more important in other well-waterproofed insects. Large changes in the humidity produced changes of less than 1° C. in the temperature excess, even at the highest air temperatures at which the insects could fly. 6. The reactions of the insects to moist and dry air are adapted to the conservation of their water rather than to rapid cooling.