The teeth of one gear are designed to mesh with those of another gear. The intermeshing teeth allow the gear to transmit the torque to its partner without slipping. Two meshing gears can move exactly synchronously. This advantage of gears is why they are found everywhere in man-made mechanical devices, from the gearbox of a car to an old mechanical watch. In 2013, two British zoologists reported their discovery that interlocking gears also occur in nature.
The researchers discovered mechanical gears in the legs of the juvenile form of an insect, the plant cicada. Cicadas are common in gardens across Europe. The insect gets its name from its powerful jumps made by quick movements of its hind legs. The jumps accelerate it from zero to twelve miles per hour in a thousandth of a second.
Without exact synchronization between its jumping legs, the cicada would get out of control. It achieves this synchronization to within a span of thirty millionths of a second. This is faster than what the animal’s nervous system could achieve. A single nerve impulse lasts more than a thousand times longer.
Instead, the zoologists found that the animal had gears in the cuticles of its legs. It achieves the necessary synchronicity by engaging these gears during the preparatory tensioning phase of the jump. But the animal’s gear system is not perfect; they are damaged by wear and tear with repeated use. In the young cicada, the worn gears are regularly replaced when the animal sheds its outer shell while moulting. The adult animal no longer sheds its skin, can fly and is no longer exposed to the same threat from predators as the young animal. It throws off the gear with its last skin.
