How Praying Mantises Could Help Build Better Robots

3-5-15 Praying mantis
Pray tell: New research examines how a praying mantis controls its spin while jumping to reach a target. Adam Hunger/Reuters

The praying mantis might be the Mikhail Baryshnikov to other wingless insects' less-coordinated Joe Shmo, at least when it comes to jumping. While many jumping insects spin quickly in the air and land randomly in response to a frightening stimulus, the wingless praying mantis jumps accurately and reliably to land on a target, all in one swift, graceful motion.

Researchers from Cambridge and Bristol universities, who have examined the mechanics of the mantises' jumps using high-speed camera footage, published their findings Thursday in the journal Current Biology.

"How on earth are they doing that?" Malcolm Burrows, professor emeritus at Cambridge's Department of Zoology, recalls thinking. "What's the mechanism that's allowing them to jump so fast, so accurately to this target?"

At an insect show, he and Gregory Sutton, a mechanical engineer currently working as a Royal Society University Research Fellow at Bristol, bought a few mantises, which began breeding back at the lab. By this time, the two men had studied a slew of jumping insects, including grasshoppers, fleas, locusts and spittlebugs. Since insects have a more visible skeletal structure, fewer neurons and are easy to acquire and rear, Sutton explains, they "are great model systems for studying movement."

Generally, Sutton explains, as something gets smaller, it's harder to control its rotation while airborne. The relatively small mantises were the first wingless insects they've observed that make such controlled jumps toward a target, and Sutton "wanted to look at the deep physical mechanics" involved.

The press release announcing the study, "Mantises Exchange Angular Momentum Between Three Rotating Body Parts to Jump Precisely to Targets," explains the process:

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.

The mantises arrive at their target at just the right orientation to land stably.

To observe the jumps, which take less than a tenth of a second from takeoff to landing, the researchers watched hundreds of high-speed videos and calculated the precise movements of the mantises.

To test their findings, the researchers set the target at varying distances in order to ensure the precise landings were not a coincidence. The researchers also did experiments on the live insects, immobilizing their abdomens with glue to study the effect. In those cases, the insect "wasn't controlling its jump properly," says Burrows, and it "just head-butted the target." In other words, they saw that if one part of the system was tampered with, it would affect the precision of the jump.

"We now have a good understanding of the physics and the biomechanics of these precise aerial acrobatics," Sutton says in the press release. But there's more work to be done. "Because the movements are so quick, we need to understand the role the brain is playing in their control once the movements are underway."

Back in engineering school, Sutton says, they would always discuss three stages of a problem. First, you have to be able to talk about it, then you have to put numbers to it, and only in the third stage can you build something.

Thursday's study would fall into Stage 2 and provides promise for roboticists who are grappling with the challenges they encounter as they build ever smaller robots, like how to control the spin of a very small robot as it jumps from one spot to another.

"Well, here's a little insect that's cracked that problem," Burrows says, and now we know how. "Maybe you could put some stabilizers on a robot's body [so it can] move like the mantis does."