A Clockwork Insect: Garden bug sports mechanical gears
Many mechanical devices have been inspired by examples in nature, but it’s not often that nature replicates something only known to be made by human beings.
Meet Issus coeleoptratus, more commonly referred to as a “planthopper”.
Photo by Malcolm Burrows
Though common throughout gardens in Great Britain, young planthoppers possess a physical trait that is spectacularly uncommon in nature: two honest-to-goodness gears on their hind legs, the only known functioning gear system of any organism. In a paper published Sept. 13 in the UK journal, Science, zoologist, Malcolm Burrows, and mechanical engineer, Greg Sutton, revealed their findings about this singular insect.
The two spent 10 years studying the movements of jumping insects at the University of Cambridge in the UK. By flipping the insects on their backs and tickling them with a paintbrush, they were able to make them kick while taking pictures of them with a high-speed camera.
When it came to planthopper nymphs, the two scientists noted something fairly extraordinary: their hind legs could synchronize their movements in 30 millionths of a second. That’s faster than a neuron can be fired off to the brain, meaning the planthopper’s legs actually start jumping before its nervous system tells it to.
Photo by Malcolm Burrows
Closer examination of the insect revealed a small system of shark fin-like gears on the first segment of its hind legs (the equivalent of the top of a human thigh bone).
As one leg prepares to leap, the interlocking gear system causes the other leg to move in almost perfect concert with the other. This synchronicity allows the planthopper to propel itself faster and farther and in a straighter path. Burrows and Sutton believe that young planthoppers evolved this trait in order to escape dangerous situations with as much speed and force as possible. At such speeds, synchronizing leg movements is absolutely vital, as one wrong move could send the insect springing to the side instead of forward.
Planthoppers actually lose their gears by the time they have fully matured, replacing them with a friction-based system of feelers. In fact, even without these gears, adult planthoppers are better jumpers than their younger counterparts. Burrows and Sutton theorize that the loss of these gears is due to them being unnecessary, as the insect is now bigger and stronger, and also because it removes the danger of damaged gears throwing the legs completely out of sync (a phenomenon the two witnessed several times).
Sutton adds that the planthopper’s unique gear system also holds potential for the way we design machines today– particularly tiny ones. Their curved and hooked gears cut down on the friction created by most gear systems found in modern devices.
“Modern machinery often doesn’t work at very small scales,” Sutton said. “Friction doesn’t matter so much when you have two big gears next to each other but when you get small, friction starts killing you.”
New methods of fabrication–such as 3D printing–make it possible to create tiny gears such as those found on planthopper nymphs.
“What we have is a prototype for incredibly small, high-speed, high-precision gears,” Sutton said. “And that prototype is given to us by nature.”