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American Association for the Advancement of Science

Gears 'invented' by insects, not humans

Photograph of an Issus nymph.
[Image courtesy of Malcolm Burrows]

Sometimes scientists study nature to learn new engineering tricks—like the researchers who modeled the wing beats of flies to create tiny, flying robots. But, other times, scientists are surprised to learn that so-called "human inventions" have already existed in nature for a long time—like the classic screw-and-nut-system, which existed in the legs of beetles long before we humans dreamt it up.

Now, researchers have realized that a particular plant-hopping insect, known as Issus coleoptratus, is such a good jumper because it has interacting gears in their hind legs that rotate just like mechanical gears. The discovery is another example of nature beating researchers to the punch.

Malcolm Burrows and Gregory Sutton took high-speed videos of the insects and found that the planthoppers have curved strips of 10 to 12 gear teeth on segments of their hind legs. However, the trait is only present in young insects (nymphs), and the gears disappear when the insects become adults, according to the researchers.

Before jumping forward, the young insects will hook the gear teeth on one leg into the gear teeth on the other leg and "cock" their legs for leaping. The action couples the insects' legs together, making sure that they both move at the same time—within just microseconds of each other—during a jump.

The findings prove that gears—once thought to be a human invention—actually evolved in nature, and that they play an important role in the behavior of plant-hopping insects.