Geared-up Insects Put the Mechanics into Biomechanics

The Museum’s newest exhibition Animals: Machines in Motion is all about biomechanics, and nothing says “mechanics” more than gears. While we see gears in all sorts of human-made machines, intermeshing rotating gears were completely unknown in nature until just three years ago when researchers at University of Cambridge looked between the legs of a little plant-hopping insect called Issus. Before you get the wrong idea about these researchers, understand that insects keep their naughty bits at their tail end and not between their legs. The reason why they were looking between insect legs is because Issus is a championship jumper and they wanted to know why. Between those legs, the researchers found a pair of interlocking gears that allow the legs to connect close to their body (below).

Interactive_gears_in_the_hind_legs_of_Issus_coleoptratus_from_Cambridge_gears-3.jpgIssus hoppers are fast hoppers, and it takes high precision to execute a fast jump. How fast is fast? The mechanical action of the jump takes place in 2 milliseconds, accelerating the insect to near 400 g-forces. For comparison, the fastest acceleration any human has survived was 46 g by Air Force Colonel John Stapp on a rocket sled in the desert. So, yeah, Issus bugs are fast—and with that speed comes a need for precision. If you have ever seen a drag race where a car starts to wobble and then catastrophically spins out of control, you can understand why Issus bugs need to fire off both legs with extreme precision. If one leg starts jumping even slightly sooner than the other, then the poor bugs would spin out of control and 2 milliseconds is not a lot of time for course corrections.

Enter our hero: GEARS! Turns out the gears don’t necessarily assist in the height of the jump but synchronize the jump. In preparation for the jump, the legs essentially “gear” into place storing up lots of jumping potential energy waiting to be released. Come jump time, the insect need only to pop the gears to synchronously spring both legs free. Fly, little Issus bug, fly!

But gears are not the only solution to this mechanical problem. Many insects jump really fast and encounter the same issues as the Issus bug, but they don’t have gears. Some use friction pads or other things that have counterparts in human-made machines. For many, we just don’t know…yet.

Feed your curiosity about the inner workings of plants and animals and explore the known and unknown at Animals: Machines in Motion, on view October 29, 2016 through January 2, 2017. 

Main image: Relative to the Issus bug, this San Diego insect exudes waxy filaments that make it look like rocket about to take off. Source: SDNHM/Berrian.

Inset image: Scanning electron micrograph of the tiny interlocking leg gears of Issus. Source: University of Cambridge (Profs. Malcolm Burrows & Gregory Sutton).



Posted By Dr. Michael Wall.

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