Gear-like structures previously found were ornamental — but these catapult-like mechanisms are a rare example of human engineering converging with evolution.
A jumping insect has gears, scientists discovered, a rare instance in which man and nature independently converged on the same idea.
It was not easy to verify. The planthopper (Issus coleoptratus) is tiny, just a bit larger than a flea. And it jumps extremely fast — with an acceleration of 200 Gs, a level close to the highest ever survived by a human.
But neurobiologist Malcolm Burrows and engineer Gregory Sutton, both of the University of Cambridge, used a high-speed camera attached to a microscope to capture the bugs in action. They put their tiny subjects on their backs on sticky wax and gently rubbed their bellies to provoke them to jump.
They found the insects have toothed gears at the base of their hind legs that inter-mesh and rotate to perfectly synchronize the timing of each limb’s release during a jump.
“It’s remarkable that these gears look so similar to the gears man has designed, even the individual teeth are so similar,” said Burrows, author of the study that was published online in the journal Science this week.
With this mechanism, the motion of the legs are always locked and coupled together. The time delay from moving one leg to another is as short as 30 microseconds, or 30 millionths of a second, allowing the insects to leap faster and farther.
Without synchronization, the body will spin instead of going straight forward due to the orientation of its hind legs, Burrows said. For example, using the most extreme case, a single-legged planthopper can only helplessly spin around in the same spot without getting anywhere.
A normal two-legged insect will still be able to leap even when its timing is off, but precious energy is wasted on rotational motion instead of a straight-ahead trajectory. When fleeing from a hungry predator, that lost distance could make the difference between reaching a safe branch and becoming dinner.
Using a catapult mechanism, the legs are able to move very quickly. In preparation for a jump, the legs cock back similar to pulling a bowstring in archery.
“You suddenly let go and the arrow goes much faster than if you were to throw it directly,” he said.
The planthoppers have gear strips on the base of either hind-leg with about ten teeth on each. However, like training wheels, the gears only exist in the nymphal stage before the insect becomes an adult. Eventually they molt away, with the adults using friction between two parts of their upper legs to synchronize their jumps instead.
Gear-like structures previously seen in animals were merely ornamental. For instance, the spiny turtle — alternatively known as a cog-wheel turtle — has a spiky-edged shell that makes it look like its carrying a gear wheel flat on its back.
“It’s a wonderful example of the exquisite use of mechanisms in nature that solve problems in a very simple way,” said University of California at Berkeley biologist Robert Full, who was not involved in the study. Full’s research focuses on nabbing ideas from animals for engineering and design inspiration.
He discovered that geckos stick to walls using millions of tiny foot-hairs, and labs have already been working on mimicking the lizard’s extraordinary traits to create a man-made adhesion technology.
Biologist Anna Ahn of Harvey Mudd College, who works in a similar field and was also not involved in the study, calls the new finding “fantastic.”
“Nowadays, bio-inspiration is sort of a catchy term,” said Ahn, but gears are unique in that man and nature independently came upon on the same idea.
Burrows and Sutton previously collaborated on experiments looking at the jumping of fleas, pygmy mole crickets and locusts.
How gears evolved in the planthoppers is unknown, but Burrows speculates that they could have begun as smaller bumps within the legs that grew larger until they became full-fledged teeth.