Embedded in the back legs of a common jumping insect are rotating gear wheels that allow the tiny creatures to leap with astounding speed.
It is the first time that anything resembling gears have been found in a living creature, and the discovery goes to show that nature often tends to beat us at our own engineering game. In this case, evolution produced gears long before people figured out how to build them.
“We always think of gears as a human invention -- we are familiar with them on our bikes and on our cars, but we never associate them with animals,” said Malcolm Burrows, a neurobiologist and biomechanist at the University of Cambridge in the United Kingdom. “It’s a very simple and neat solution to what would otherwise be an incredibly difficult problem.”
Common in both North America and Europe, the planthopping insect called Issus can’t fly but it is able to launch itself with impressive power and speed by pushing off with its two hind legs. As adults, Burrows said, the insects accelerate faster than a Ferrari.
Unlike grasshoppers, whose legs are located on the sides of its trunk, Issus’ legs lie beneath its body. That creates a problem. Whereas a grasshopper can push off with one leg and still hop straight, a planthopper that tried jumping with just one leg would spin rapidly around the axis of its body.
Instead, the insect’s two rear legs move with remarkable coordination.
To better understand how, Burrows and colleague Gregory Sutton took high-speed videos that captured up to 30,000 frames each second of Issus nymphs as they jumped.
The images showed that the insect’s two hindlegs always moved within 30 microseconds of each other. A microsecond is one millionth of a second, and 30 microseconds is significantly less time than it takes for a single nerve impulse to reach the muscles in the animal’s legs.
Because their nervous systems are too slow to synchronize movement of the hind legs, the insects have developed a mechanical solution. Close-up high-speed images revealed gear wheels on each hind leg with about a dozen teeth that interlock, the researchers report today in the journal Science. These gears ensure that the force of movement transfers almost instantly from one leg to the other.
“Their gears are remarkably similar to the way we build gears,” Burrows said. “Insects obviously evolved this mechanism many millions of years ago and we only got around to it fairly recently.”
Gears are an unexpected discovery in insects, said Ronald Hoy, a neurobiologist at Cornell University in Ithaca, N.Y. But evolution has a knack for coming up with surprising solutions for all sorts of thorny problems.
“I think it speaks to the idea that there’s nothing new under the sun,” Hoy said. “Whatever we’ve been able to come up with, if you look hard enough in the animal kingdom, you’re going to find a counterpart.”