Active Ventilation

Although most gas exchange in insects occurs through diffusion (passive ventilation), in some cases it is inadequate to meet the oxygen needs of insects, particularly large or flying insects. Thus, muscular contractions acting via hydrostatic pressure (pressure on the hemolymph) compress the trachea and air sacs to force carbon dioxide out and allow more rapid intake of air.

The exact mechanism varies among taxa, but usually involves contraction of the abdomen, and synchronization of opening and closing of the spiracles.