Thermoregulation in Insect
In insects, as in other animals, body temperature strongly affects the rate of energy expenditure, the rate at which food can be located and harvested, growth, the facility with which mates can be acquired and predators avoided, and sometimes also the susceptibility to disease organisms. Thermoregulation refers to the ability to regulate that body temperature which best serves survival and reproduction, and it encompasses numerous conflicting constraints and selective pressures. In insects, major considerations involve body mass and access to either external or internal heat. Thermoregulation operates through behavior, physiology, and morphology. For the most part, insects are too small to be able to appreciably elevate, or regulate, their body temperature by internal heat production, although some are large enough and that, coupled with their high flight metabolism, could easily cause them to overheat. In numerous insects, elaborate mechanisms of thermoregulation have evolved both for heating and for cooling the body that possibly rival those of the typically endothermic vertebrates.
Insects arose on earth at least 350 mya in the Devonian Period of the Paleozoic Era. Little is known about the earliest forms, except that originally they must have been crawlers, not flyers, and their bodies assumed approximately the temperature of the immediate surroundings to which they adapted. This holds true even when the immediate surroundings are quite frigid. The adult form of a flightless midge (Diamesa sp.) walks on glacier ice even when its body temperature is chilled to — 16°C. It is so sensitive to heat that, when taken from its natural environment and held in one’s hand, it is killed by the warmth of one’s skin. However, there are insects that maintain quite specific and high body temperatures. Some species of sphinx moths, for example, have thick insulating fur and normally maintain a thoracic temperature near 46°C during flight over a wide range of ambient temperatures. To these moths, our own normal body temperature of 37°C is almost cool. An insect’s head and abdominal temperatures are for the most part unregulated.