A jumping insect has gears, scientists have 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 in England, 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.
”It’s remarkable that these gears look so similar to the gears man has designed, even the individual teeth are so similar,” said Professor Burrows, author of the study that was published online in the journal Science.
With this mechanism, the legs are 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 synchronisation, the insect’s body will spin instead of going straight forward due to the orientation of its hind legs, Professor 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 10 teeth on each.
However, like training wheels, the gears only exist in the nymphal stage before the insect becomes an adult. Eventually they moult away, with the adults using friction between two parts of their upper legs to synchronise 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 it’s carrying a gear wheel flat on its back.