Step aside, human inventors—
insects have been using mechanical gears much longer than humans have. Scientists report today they have found that young insects from the group known as planthoppers, pictured above, have interlocking gears in their hind legs that allow them to cock their stance and jump at high speed.
Malcolm Burrows and Gregory Sutton of the University of Cambridge took high-speed videos of the leg movements of nymphs of the planthopper Issus coleoptratus. Each nymph was filmed as its back was restrained but its legs were free to move about.
They found that, in preparation for a jump, the insect cocks its hind legs by locking the gears of their hind legs together. In less than 80 microseconds, the two strips of 10 to 12 tiny teeth are engaged. From there, the fastest hoppers took off in just 2 milliseconds at a velocity of 3.9 meters per second, or almost 9 miles per hour.
Each of the Issus gear teeth is curved, and the gears work only in one direction. The researchers tested the fine-tuned synchronicity of the hind-leg gears and found
that moving the tendon of the jumping muscle on one leg automatically led to movement in the other leg, even in a dead planthopper.
The researchers also found that the torque travels differently through the gear sets. Teeth responsible for the beginning of the jump in one leg will transfer power to the teeth of the stationary leg. While the planthopper’s motor neurons help in this synchronous behavior, the team found that it’s the gears that ensure the legs move together smoothly.
“The gears in Issus…demonstrate that mechanisms previously thought only to be used in manmade machines have evolved in nature,” they write in the paper, which is published in Science.
This specialized gearing then disappears during the nymph’s final molt before it becomes an adult—the gears, it turns out, are just baby teeth.
Photo by Suede Chen / Shutterstock
Video courtesy Malcolm Burrows