Leap of the Flea

In all of nature, there is hardly a more impressive athlete than the tiny flea. The pesky wingless insects are not only able to jump distances of more than 100 times their body length, but they also make the jumps repeatedly, apparently without tiring. The Oriental rat flea, for instance, can hop steadily for three straight days 600 times an hour. Now a group of researchers, led by British Entomologist Miriam Rothschild (of the banking family), believes that it has uncovered the secret of the flea's remarkable prowess.

The main propulsion for the great leaps comes from the large and powerful hind legs. But, the researchers report in Scientific American, the muscles there seem inadequate for the job. For one thing, even the fastest possible single muscle contraction could not move the legs rapidly enough. Moreover, muscle efficiency invariably decreases with temperature; yet the flea seems indifferent to cold. Even when the temperature drops close to freezing, its jumping ability seems largely unimpaired.

To find the flea's lous source of energy, the researchers turned to high-speed motion picture photography (3,500 frames per second) and chemical analysis. They soon determined that it was hidden in a region filed the pleural arch near the base of the flea's hind legs. In flying insects, the pleural arch is the site of the wing-hinge ligaments, the place where the wings are attached to the exoskeleton, hard outer covering. In fleas, as well as in dragonflies, locusts and certain other insects, the arch serves another purpose: as a repository for an extraordinary elastic-like clump of protein called resilin that can be stretched, and contracted back to its original shape, faster than any known rubber.

As the flea prepares to jump, it crouches like a runner in the starting block, lowering it's head and contracting its body. Thes actions compress the resilin and engage hooklike "catches" in the flea's exoskeleton that prevent the resilin from expanding prematurely. In effect, the flea has "cocked" itself for the leap. Then, at the right moment, it releases the catches. The resilin snaps back to its original size, like an uncoiling spring, and exerts a sharp downward force on tendons connected to the upper part of the hind legs. That launches the flea into the air. In fact, lift-off occurs so rapidly that the flea reaches peak acceleration of 140 Gs -- more than 30 times that endured by astronauts during the launch of the Saturn 5 moon rocket.

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