Greg Sutton was closely inspecting the back legs of a planthopper nymph — a small green, flightless insect — when he noticed something odd.
There was a tiny row of bumps on the inside of each leg where it met the insect's body. The bumps looked just like the teeth of gears. And when the planthopper jumped, they acted like gears too — as teeth meshed, the legs turned in synchrony. Sutton says his finding, published this week in Science, is the first mechanical gear system ever observed in nature.
He's now a post-doc at the University of Bristol, in England. But while working at the University of Cambridge, Sutton spent a lot of time studying the kicking mechanism of various jumping bugs — grasshoppers, planthoppers, leafhoppers.
He would place the insects on their backs and tickle them with a paintbrush to make them kick (the motion was identical to jumping). They kicked fast. While most humans take half a second to jump, the planthoppers only take a couple of milliseconds.
To capture that action, Sutton used high-speed cameras shooting at a rate of 20,000 frames per second. To get good exposure at such a high frame rate, he illuminated the insects with lots of bright lights.
"You're using so much light that you may end up cooking the animal," Sutton says.
Still, he was able to observe a few kicks before switching out the insects. And he noticed something. They kicked with incredible, almost impossible synchrony — flexing within 0.05 milliseconds of each other.
That's faster than neurons fire.
"So we were asking ourselves, 'How in the world did they get such precise synchrony between the left and the right legs?' " Sutton says.
That led to a closer inspection of the nymph's anatomy and the discovery of the gears.
The teeth of these natural gears don't look quite like man-made versions. The vast majority of man-made gears follow the same precise pattern, one proposed more than 200 years ago by Leonhard Euler.
Euler was a Swiss mathematician, one of the most influential in history. His colleagues called him "Analysis Incarnate." One rhapsodized that Euler "calculated without any apparent effort, just as men breathe, as eagles sustain themselves in the air."
Euler wrote dozens of books on mathematics, but still found some spare time to fiddle with gears. He figured out that an infinite number of cog shapes could be used in machines, but Euler settled on one that could be easily constructed by contemporary tools. That shape (seen below, next to Euler's portrait) is still used in most machines today.
Thanks to modern fabrication techniques like 3-D printing, engineers are now free to explore less orthodox gear shapes. They are looking for gears that work best for specific applications — as in tiny machines.
"There's a lot of debate over how you design these kinds of machine parts over very small size ranges," Sutton says.
Planthopper gears certainly are tiny. Each tooth is only about 20 micrometers wide — a fraction of the width of a hair. And the teeth of the insect gears are more curved and hooked than typical man-made gears.
"What we have is a prototype for incredibly small, high-speed, high-precision gears," Sutton says. "And that prototype is given to us by nature."
Gear Shapes In Nature (That Don't Work)
Gear shapes have been discovered in nature before, but until now, none of them has been shown to work.
1. Last year the image below made the rounds on the Internet, purportedly showing gears trapped in an ancient rock. Tabloids trumpeted the discovery of a 400-million-year-old machine left by aliens or time travelers.
Nope. Those "gears" turned out to be the fossilized stems of crinoids — aquatic creatures related to sea urchins. (You can see an intact fossil below to the left.) Their relatives still survive in reefs today (below right).
2. Heosemys spinosa — also known as the cogwheel turtle — is named for the spines on its shell. Members of the species have never been known to pair up, link cog-teeth, and spin in opposite directions ... though that would certainly be an amusing sight.
3. Adult Arilus cristatus — wheel bugs — are equipped with a cog-like plate of armor on their backs.
4. Crocodile hearts have a special valve — called a cog-teeth valve — that helps them regulate blood-flow. The cog-teeth can be briefly glimpsed in the video below, which was taken inside a beating crocodile heart.
STEVE INSKEEP, HOST:
You can find gears in just about every manmade thing that has spinning parts: analog watches, cars, coffee grinders, my bike. Turns out you can find them in nature, too. In this week's Science magazine, researchers announced the unexpected discovery of a rotating gear system in the legs of an insect.
As NPR's Adam Cole reports, these naturally made gears help the bugs jump at lightning-fast speeds.
ADAM COLE, BYLINE: The planthopper is a little grey-green insect, a cousin of the grasshopper, with veined wings that look a bit like leaves. The juveniles, called nymphs, are slightly larger than a flea, but their tiny legs can still pack a punch.
GREG SUTTON: Have you've ever been kicked by a grasshopper?
COLE: I have never been kicked by a grasshopper. Well, I don't know if I'd feel it if I had.
SUTTON: Oh, you will feel it.
COLE: That's Greg Sutton who has been kicked by a grasshopper. He's a scientist at University of Bristol in the U.K., and he knows first hand that grasshoppers and their insect relatives have powerful back legs - good for kicks, and great for quick jumps. Planthopper nymphs are some of the best jumpers around. They can launch themselves hundreds of times their own height into the air in just a couple milliseconds.
SUTTON: It's such a short time, it's difficult to think about.
COLE: Now, jumping is trickier than you might think. You have to make sure both legs push off at exactly the same time; for example, when LeBron James goes up for a jump shot.
UNIDENTIFIED MAN: James pulls up...
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COLE: In that moment, if one leg pushes off before the other, he'll go careening sideways. But, of course, that doesn't happen.
UNIDENTIFIED MAN: ...puts it in. Thirty-five...
(SOUNDBITE OF CHEERING)
COLE: Jumping is easy for James. After all, his jumps last a full 500 milliseconds. His neurons have plenty of time to their send messages to both legs so they'll kick simultaneously. And if they are a few milliseconds off, it's no big deal.
But planthoppers jump so fast they only have a couple milliseconds to synchronize their legs. If they're off by even a little, the jump will go haywire. But Sutton says they get it right almost every time.
SUTTON: Usually the legs extend within 50 microseconds of one another.
COLE: That's a tiny fraction of a millisecond. And here's the thing: that's faster than their neurons can fire.
SUTTON: So we were asking ourselves how in the world did they get such precise synchrony between to the left and the right legs?
COLE: So Sutton and his colleagues watched hundreds of slo-mo jump videos, and examined the planthoppers' legs under a microscope.
SUTTON: And we noticed these bumps.
COLE: A row of bumps along the curved inside edge of each planthopper hip, they looked like the ridges on two tiny cogwheels.
SUTTON: Before the insect jumped it would engage these ridges.
COLE: And the bumps would mesh together perfectly. When one leg moved, the other leg would move with it. You can watch a close-up video of this on our website, and it really is a working gear system - the first ever seen in nature.
This is a big deal for biologists but the design of the planthopper gears has engineers excited too. Sutton says most human gears follow the same pattern.
SUTTON: If you see a set of gears, say, pull out your watch or if you look up gear on the Internet, you'll see a shape of tooth over and over and over and over again.
COLE: But planthopper gear teeth are quite different, they're hooked and rounded.
SUTTON: So what we have is prototype for incredibly small, high-speed, high precision gears. And that prototype is given to us by nature.
COLE: Maybe one day we'll replicate the planthopper gears using new techniques like 3D printing, and put them to work in human machines.
Adam Cole, NPR News
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INSKEEP: And, as Adam mentioned, you can see a video of these insect gears in action, it's pretty amazing. It's at our website, npr.org.
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INSKEEP: This is NPR News.
(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.