Long before human beings started using them in machinery, gear systems that worked through mechanical interaction existed in the morphology of many living creatures. Researchers have recently discovered that in the nymph (immature) forms of the insect Issus coleoptratus, a species of planthopper, there are gear systems in the inner section of the rear legs’ hip joints. These gear systems disappear during the final skin-shedding (ecdysis) as the nymph turns into a mature insect. Such a biomechanical transformation likely takes place due to hormonal changes.
Locusts and other similar creatures manage to jump thanks to the strong, fast movements of their rear legs. Unfortunately, since locusts have legs loosely connected to their main body, they do occasionally wobble or divert from their target. Issus coleoptratus, on the other hand, has a gear system in its rear leg joints that are inside the main body. This allows the insect to jump without diversion. In addition, the two rear legs move with the same angular velocity, also thanks to this gear system.
The machinery in Issus coleoptratus is perfectly designed for its task, showing the handiwork of a master craftsman. Every gear in the nymph form is 350-400 µm (microns) long and is made up of 10 to 12 teeth. Please note that a micron is one millionth of a meter. If a tooth is broken in one of the gears, it is repaired during the skin-shedding process. Front teeth are 80 µm long; yet the teeth are gradually shorter toward the rear, down to 30 µm. The teeth are extremely ossified. The fact that these teeth do not lose their dimensions due to friction and abrasion is really amazing. Moreover, the gears in the rear legs of the nymph form of this insect are asymmetric, while the gears we humans manufacture are symmetric. These gears are functional in the synchronous mechanical movement of the insect.
It has been determined through high-speed camera systems that the rear legs of Issus coleoptratus are fast and synchronous while the creature jumps. The speed of both rear legs while jumping is equal to a wheel during at 33,000 RPM (revolution per minute) – or 550 in a second. Please keep in mind that typical cars have a maximum of 8,000 RPM.
It has also been recorded that the gears are strongly engaged during the preparation and the pushing movement for a jump. In this impeccable functioning, gears have revolved through engaging approximately 50,000 times in a second. During this process, power is transmitted to the legs equally and without loss. The front legs start moving in two milliseconds and reach a speed of 3.9 m/s. The gears in the rear legs start moving even faster (within one millisecond) and jump with a speed of 5.5 m/s.
At this speed, Issus coleoptratus can be exposed to a force of 500-700 G, compared to its body mass. The magnitude of this force becomes more comprehensible when one considers that the regular gravitational force is 1 G; pilots can withstand a force of 9 G; and airplanes can endure 11 G. And yet Issus coleoptratus can withstand up to 50 times more force than an airplane.
- Science, “Interacting gears synchronize propulsive leg movements in a jumping insect”, 13 September, 2013.