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Insects that inhale

To move blood to particular places in their bodies, some flies can reverse their heartbeat — the equivalent of you reversing the direction of your blood flow!
When you breathe, you actively push air molecules in and out of your lungs — this process of ventilation brings a fresh supply of oxygen to your cells. Many insects, on the other hand, rely solely on diffusion — but others have boosted the efficiency of their respiratory systems by evolving a means of ventilating their tracheae. But how do they manage to do this? After all, insects don't have lungs...

Insects that ventilate have evolved structures called airsacs — enlarged areas of a trachea that can change in volume. Like squeezing the rubber bulb of a turkey baster, changing the volume of an airsac causes air to flow in or out of the airsac and the connecting tracheae. Insects compress airsacs by pumping blood around their bodies — for example, pumping blood out of the abdomen and into the thorax would cause airsacs in the thorax to compress and airsacs in the abdomen to expand, allowing oxygenated air to rush in. This process increases the efficiency of the respiration and is especially important for insects that use a lot of energy flying, a process that requires plenty of oxygen.

Fly tracheae and air sacs