Insect Jumps with 'Mechanical Gears' in its Legs: Functioning Interlocking Cogs in Nature

Scientists have long thought that functioning gear mechanisms could only be human-made. Yet it turns out that isn't the case. Researchers have discovered a natural example of this mechanism in a common insect, revealing that evolution created interlocking cogs first.

The insect in question is the juvenile Issus, a creature that can be found in gardens all across Europe. It's known for its ability to jump and has specialized hind-leg joints. More interestingly, though, are the curved cog-like strips of opposing "teeth" that intermesh on these joints and that rotate like mechanical gears to synchronize the insect's legs when it jumps.

These biological gears actually resemble those found on every bicycle and inside every car gear-box. Each gear tooth has a rounded corner at the point it connects to the gear strip, which is essentially a shock-absorbing mechanism to stop teeth from shearing off. The gear teeth on the opposing hind-legs lock together and ensure almost complete synchronicity in leg movement.

"This precise synchronization would be impossible to achieve through a nervous system, as neural impulses would take far too long for the extraordinarily tight coordination required," said Malcolm Burrows, lead author of the new paper, in a news release. "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, creating absolute synchronicity."

Yet Issus doesn't maintain these gears forever. Although they're present in the juvenile stage of the insect, they're lost during the final transition to adulthood. Researchers aren't quite sure why these insects lose their gears, but it could be the potential fragility of the gear system. If one "tooth" on the gear breaks, the effectiveness of the whole mechanism is damaged. While this could be repaired between the juvenile and adult phases during a molt, on an adult it would remain permanent.

There might be another reason for the lack of gears in adults, as well. Adults are far larger, which means that their "trochantera," the insect equivalent of the femur of thigh bones, are also bigger. These larger trochantera might allow them to create enough friction to power the enormous leaps from leaf to leaf without the need for gear teeth.

The findings reveal a little bit more about these evolutionary gears. In fact, this is the first example of a natural cog mechanism with an observable function in nature.

The new study is published in the journal Science.