M. Burrows et al/Current Biology 2015
Before they grow wings and fly, young praying mantises have to rely on leaps to move around. But these little mantises are really good at jumping. Unlike most insects, which tend to spin uncontrollably and sometimes crash land, juvenile praying mantises make precision leaps with perfect landings.
But how do they do that? To find out, Malcolm Burrows of the University of Cambridge in England and colleagues filmed 58 juvenile Stagmomantis theophila praying mantises making 381 targeted jumps. The results of their study appear March 5 in Current Biology.
For each test leap, the researchers put a young insect on a ledge with a black rod placed one to two body lengths away. A jump to the rod was fast — only 80 milliseconds, faster than a blink of an eye — but high-speed video captured every move at 1,000 frames per second. That let the scientists see what was happening: First, the insect shook its head from side to side, scanning its path. Then it rocked backwards and curled up its abdomen, readying itself to take a leap. With a push of its legs, the mantis was off. In the air, it rotated its abdomen, hind legs and front legs, but its body stayed level until it hit the target and landed on all four limbs.
“The abdomen, front legs and hind legs performed a series of clockwise and anticlockwise rotations during which they exchanged angular momentum at different times and in different combinations,” the researchers write. “The net result … was that the trunk of the mantis spun by 50˚relative to the horizontal with a near-constant angular momentum, aligning itself perfectly for landing with the front and hind legs ready to grasp the target.”
Conservation of angular momentum is key to a perfect landing here. It lets the praying mantis rotate its body and line itself up just before hitting the target. Other animals also exploit this quirk of physics, the researchers note. There are species of lizards, for instance, that use their tails as reservoirs of angular momentum, and falling cats, which rotate their front and back parts of their bodies, also use conservation of angular momentum to land on four feet.
To test what would happen if a praying mantis couldn’t rotate its parts, the researchers did something kind of mean — they superglued the abdomens of two of the insects. When those young ones made a jump, they couldn’t line themselves up for landing. They under-rotated, couldn’t grasp the pole and sometimes even collided with it head first. Ouch.
A young praying mantis controls its jump by rotating its abdomen to adjust its center of mass and regulate spin. When the insect can’t move its abdomen (because scientists glued its segments together), the praying mantis can’t control its jump and lands headfirst.
Video credit: M. Burrows et al/Current Biology 2015