How Insects Fly

With their proportionately bulky bodies supported by puny wings, many flying insects look about as airworthy as a Mack truck. French Zoologist Antoine Magnan once studied bumblebees for several years, reached the conclusion that their ability to fly defied all known physical principles. The secret of this kind of flight lies in rapid wing beats. The tiny midge beats its wings 1,000 times per second to stay airborne, each beat contributing a minute amount of lift.

Scientists have long known that the muscle contractions necessary to produce these rapid wing beats are not triggered individually by nerve stimulus, as in birds. Nerves cannot work that fast. How then does the midge fly? In Britain's New Scientist, Professor Vincent B. Wigglesworth, extracting reports by other European scientists, supplies the answer: midges--and presumably other similar insects--are automatic flying machines. A midge's muscular motor works in much the same way as a piston engine. Once the ignition is turned on. the engine keeps running until the ignition is turned off or the fuel exhausted.

Midge flight is controlled by two sets of opposed, springlike muscles in the insect's thorax. Acting through elastic structures in the thorax wall, one muscle set draws the wings up, the other pulls them down. At a specific point on the upswing, the wings "click" to a fully elevated position, the elevating muscles automatically relax, and the tautly stretched depressing muscles take over. The same sequence is repeated on the downswing. The flying muscles do not need to be triggered by nerve commands. The insect's nerves serve only to start and stop the process--like the car's ignition.

Insect muscles that burn fat are fairly economical, but those that burn carbohydrates such as glycogen are lavish with fuel. Reports Wigglesworth: the carbohydrate-fueled fruit fly, Drosophila, can stay aloft for five hours at a stretch, but it beats its wings 250 times per second, and it burns up 10% of its body weight during an hour's flight--proportionately as much fuel as a 600 m.p.h. jet airliner. Drosophila's cruising speed: 2-3 m.p.h.

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