Gears are a potent symbol of human industry, a sign of mechanical wonder or a cold assembly line. If you had to pick something to stand against the natural world, they'd be a pretty likely pick — except that as it turns out, insects discovered them first. In a paper published today in Science, Malcolm Burrows and Gregory Sutton of the University of Cambridge reveal that the plant-hopping Issus coleoptratus leaps with the aid of a pair of tiny, one-way gears, the first functional ones ever found on an animal.
The gears aren't connected all the time. One is located on each of the insect's hind legs, and when it prepares to jump, the two sets of teeth lock together. As a result, the legs move in almost perfect unison, giving the insect more power as the gears rotate to their stopping point and then unlock. Lead author Malcolm Burrows says this method lets it jump without relying on a nervous system that simply wouldn't be fast enough. "By developing mechanical gears, the Issus can just send nerve signals to its muscles to produce roughly the same amount of force — then if one leg starts to propel the jump the gears will interlock."
Despite their usefulness, the gears only exist for part of the insect's life. As it grows out of its nymph stage, it keeps its powerful jump but sheds the gears, for unknown reasons. Burrows hypothesizes it could be because the older Issus is strong enough to jump without the extra benefit of the locking system. But it could also be because of a fundamental mechanical problem. Like man-made ones, the gears on Issus' legs can be damaged over time. As a nymph, it can molt periodically, repairing the injury. But once it becomes an adult, that option no longer exists. And unlike man-made gears, there's no cog that can replace an Issus leg segment with a broken tooth.