To watch a young, wingless praying mantis jump is a truly remarkable thing. The jump from take-off to landing lasts less than a tenth of second--literally faster than the blink of a human eye. During a jump, the insect's body rotates in mid-air at a rate of about 2.5 times per second. And yet, according to researchers who report their observations in the Cell Press journal Current Biology on March 5, the mantises' jumps are precise. When mantises jump, they land on target every time.
"This is akin to asking an ice skater who is rotating at the same speed as these mantises to stop suddenly and accurately to face a specific direction," says Malcolm Burrows of the University of Cambridge.
Burrows, along with Gregory Sutton of the University of Bristol, came to study praying mantises quite by accident. After buying a few mantises at an amateur entomology show, the researchers brought them back to the lab. Those insects started breeding, and the researchers became intrigued by the mantises' jumping behavior.
"We could not scare them into jumping or get them to jump away from a threatening stimulus," Sutton says. "So instead we offered them a target to jump towards and found that they would do this consistently and accurately."
The question then was: How did they do it?
To find out, the researchers watched high-speed video after video--381 in all--of 58 young mantises jumping to a thin black rod. What the researchers saw was this: in preparation for a jump, first the insects sway their heads sideways, scanning for their targets. Then they rock their bodies backward and curl their abdomens up, tip pointed forward.
With a push from their legs, the mantises' bodies launch into the air, spinning in controlled fashion. The insects rotate three distinct body parts--the abdomen, front legs, and hind legs--independently and in a complex sequence. As the mantises sail through the air, the spin is transferred from one body segment to the next, keeping the body as a whole level and right on target.
"Maintaining stability so that the body does not rotate uncontrollably in mid-air is a difficult task," Burrows says. "When the movement is rapid, as it is in a jump, and you don't have wings, then the task is even more difficult. Nevertheless, a praying mantis moves rapidly and controls the rotation of its body so that it lines up precisely with a target, and does all of this in less than 100 milliseconds." (That's a tenth of a second.)
This kind of jumping control is rather unusual in the insect world. Most insects lose all control once their legs leave the ground, the researchers say, spinning in unpredictable directions with frequent crash landings.
The young mantises' newfound skill might have applications for tiny robots. And there is plenty more to learn about the insects themselves, too.
"We now have a good understanding of the physics and the biomechanics of these precise aerial acrobatics," Sutton says. "But because the movements are so quick, we need to understand the role the brain is playing in their control once the movements are under way."
Current Biology, Burrows et al.: "Mantises Exchange Angular Momentum between Three Rotating Body Parts to Jump Precisely to Targets"
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