Energetics

Flying consumes huge quantities of energy. Metabolism of flying insects depends upon an extremely efficient and miniaturized system specialized to deliver oxygen to where it is used and to remove heat and carbon dioxide from where these are made.

Thoracic flight muscles have the highest known mass-specific rates of oxygen consumption. Tracheoles are oxygen's closest contact with tissues. Blind-ended tracheoles often penetrate deep into muscles reducing the distances oxygen must travel. Diameters of tracheoles are about the distance of the mean free path-length for oxygen. The mean free distance is the distance a molecule travels on the average before it collides with another molecule. Oxygen enters the mitochondria, the cellular powerhouses, that supply the phosphate containing ATP molecules the contracting muscles need for aerobic metabolism. Mitochondria oxidize fuels they receive from the hemolymph to make carbon dioxide and water. Molecules of carbon dioxide exit the mitochondria of the flight muscles, to circulating hemolymph that transports them through the body and delivers them to the air.

Tapering of the abdomen compensates the limits to diffusion of heat and carbon dioxide from respiration by the exoskeleton and the cuticle and the nature of the tracheae. Bernoulli entrapment of air in the tracheae aids gas exchange. High external velocities of airflow over the posterior spiracles during flight create a gradient of pressure. This gradient drags air into the anterior spiracles and, thereby increases bulk flow of air through the respiratory system. Respiration and circulation are coordinated in that respiratory and locomotory movements also help to circulate hemolymph.

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