Long before humans assembled gears into watches and car transmissions, the planthopper insect in the genus Issus evolved gears of its own. An interlocking gear structure synchronizes the movement of the insect's hind legs during a jump and prevents it from spinning out of control like a plane that has lost control of its yaw. The juvenile planthopper, called a nymph, has a row of 10 to 12 teeth on the inner surface of each back leg, which engage and force the legs to move in unison. High-speed video reveals that, thanks to the gears, the two legs spring into action within 30 microseconds of each other . Without the gear structure, such synchronized movement would be difficult, as the spike in neural activity that generates this movement lasts much longer, about 1 millisecond, the group reports online today in Science. Curiously, adult planthoppers lack such gears but seem to be better jumpers anyway, perhaps because, with their larger bodies, they can more easily rely on friction between the surfaces of their legs to keep them synchronized.