In A Nutshell
The juvenile planthopper jumps with incredible force, accelerating with more than 200 Gs of pressure with each hop. To synchronize their legs, they’ve evolved a pair of interlocking gears so that each leg pushes with the same amount of force. Otherwise, they’d spiral out of control.
The Whole Bushel
In nearly every instance since the dawn of time, it’s humans who have copied nature to create something new. As it turns out, we didn’t even completely beat nature to mechanical gears. The planthopper is the first case found in nature of a gear-like structure inside a living organism—at least, a functional set of gears. Several other creatures, like the wheel bug, have gear-shaped parts, but they don’t serve a purpose other than passive defense or fashion.
For the planthopper, the gears are as vital to its survival as legs or wings are to other insects. Planthopper species are found in most parts of the world, and most of the time they use camouflage for defense. The different species have evolved to look remarkably similar to the leaves of their natural habitats, so they’re usually pretty safe from prowling birds. But young planthoppers—the juveniles—don’t have that protection yet. Instead, they rely on being able to jump quickly from one plant to the other, usually in the blink of an eye.
And that’s not an exaggeration—it only takes 30 millionths of a second for a juvenile planthopper to extend its legs and launch into the air—literally faster than a neuron moving from one part of your brain to another. To manage that force, the two gears at the base of their legs connect with interlocking teeth and spin at the same rate, keeping the legs moving at exactly the same speed. What’s so remarkable about the gears—other than the fact that they exist—is the way they’re so intricately designed. The gears are crescent-shaped and each have around 10 teeth, which are rounded to reduce friction and rotate freely within the planthopper’s exoskeleton. And whenever the juvenile sheds its skin, any damage to the gears is repaired with the new layer of skin. When the planthopper reaches adulthood, the gears simply disengage and fall off.
Mechanical legs like this also represent a simple solution to a complex problem. When most insects jump, their brain sends a signal to their leg muscles, which then relay a second signal back to the brain that tells the brain what position their legs are in. This lets the brain coordinate the movements. However, that signal takes time to bounce back and forth. In the planthopper, the brain doesn’t need to coordinate anything; it just sends a single message: jump. The muscles don’t need to push with an equal amount of force, nothing complex needs to happen, because the gears cancel out the extra oomph so that both legs move perfectly together.
The result is something like a catapult—the planthopper’s legs cock back into firing position, then explosively release and pop the insect into the air. This is the first example that researchers have found of nature and humans creating the same thing separately. It’s pure organic machinery.