How to jump, mantis style
Scientists have uncovered how young praying mantises manage to land cleanly every time when jumping between branches.
Researchers at Cambridge University used high-speed video cameras to capture extremely detailed footage of the moments before, during and after a jump.
It's all about controlling the spin that's generated when the force of a jump is exerted by the legs. This is to ensure that the jumper lines up with the target and doesn't crash straight into it.
Just before making a jump, the mantis scans the target by moving its head from side to side to determine how far away it is. It then curls its abdomen over to adjust its centre of gravity, ready for takeoff.
When the legs launch it into the air, the spin generated starts to rotate the mantis. The new footage reveals that, once airborne, it moves its front legs, back legs and abdomen in precise coordination, adjusting and stabilising its orientation to match the landing zone.
"This rotation of the limbs and abdomen stores angular momentum," explains Prof. Malcolm Burrows of Cambridge University, "and means that the body itself doesn't rotate as much and remains stable."
Once it arrives at the target branch, the mantis grasps it with all six legs and continues on its way.
To investigate the mechanism in more detail the team constructed a computer model of the jumping mantis, which they could manipulate in any way they wanted. By tweaking certain parameters they could see what would happen if certain movements were restricted. If, for example, the mantis didn't curl its abdomen, it wouldn't generate enough spin and the model predicted it would crash headfirst into the target branch.
The next step was to test this prediction by restricting the movement of a real mantis and recording it jumping. The team did this by gluing the abdomen of the unfortunate mantis into a fixed position. The result? Just as the model predicted, the mantis didn't rotate enough, resulting in a spectacular faceplant (which thankfully left the mantis unharmed).
Understanding how this intricate series of movements provides mid-air stability could help in the field of robotics. Jumping robots suffer from the same spin problem as the mantis, but until now roboticists have been unable to design a solution. By studying how the mantis solves this problem we could open up new possibilities for the robots of the future.
"We [humans] have only been trying to design things ourselves for a few tens or hundreds of years," continues Prof. Burrows, "so why not take advantage of what's gone before us, billions of years of history, providing solutions that may be of use in our designs?"
Click the links below to see videos:
A mantis jumping to target:
A mantis with fixed abdomen jumping to target: