Walk Of The Locust May Help Predict A Swarm

HOWARD BERKES, host:

People who grow crops in places like West Africa and parts of Australia tend to panic when they hear this.

(Soundbite of locust swarm)

BERKES: That's the sound a giant swarm of locusts make when descending on farmers' fields. By the time they hear this roar, it's usually too late to do anything but wait for the plague to pass. At the moment scientists have a hard time predicting the movements of locust swarms, but that may be changing. NPR's John Nielsen has more.

JOHN NIELSEN reporting:

The desert locust is the Doctor Jekyll of the insect world. Most of the time it looks like an ordinary grasshopper, wandering quietly and keeping to itself. But every now and then, unexpectedly, it turns into Mr. Hyde. Those ordinary-looking grasshoppers start growing wings and assembling. Next thing you know they've formed voracious flying swarms that can be measured by the mile. Lots of people have seen these swarms, but few have seen them forming. One of the lucky ones is Ian Cousins, an entomologist at Princeton University who once joined a road trip through the deserts of West Africa.

Professor IAN COUSINS (Entomologist, Princeton University): We were driving along with the windows open, and suddenly a thump against the back windshield and a locust came flying in through the front window and was flying around inside the truck, and then it just - they get more and more and more. And suddenly, you know, we realized that we're within a swarm.

NIELSEN: The truck stopped. Cousins jumped out, looked at the ground, and gasped. Locusts that were just then growing their wings, stretched to every horizon, he says.

Prof. COUSINS: It was astonishing, this seething mass of these insects, like some animate fluid as it crosses the desert, all moving in the same direction as each other.

NIELSEN: Cousins has long wondered how these swarms remain so incredibly organized. Now, in the latest issue of the journal Science, he and some colleagues say they've figured out a big part of the answer. First, they stuck a couple of locusts into a transparent tunnel and watched them wander around aimlessly. Then, when they added more, they saw a highly organized swarm begin to take shape. David Sumpter, mathematician at Oxford University, says the swarm stayed organized because the locusts appeared to be hard-wired to do one simple thing.

Professor DAVID SUMPTER (Mathematician, Oxford University): The basic rule is that you line up with anyone near to you. So you look around, you see what direction others are going in, and you start to have a tendency to move more in that direction.

NIELSEN: Sumpter and his colleagues have now created mathematical models that can predict the formation of locust swarms, at least in a laboratory setting. They show that when locust groups are small, individuals can break away.

Prof. SUMPTER: But if there's a high enough density of you, then you will all start to line up and eventually you'll all be going and walking in the same direction.

NIELSEN: Those walks lasted for hours, Sumpter said. Then, like soldiers in an army on parade, the locusts would turn around and march the other way. Rapid turns like those seem to be a sign that a giant swarm will soon be forming. Findings like these could make it easier for scientists to better predict the emergence of a locust swarm, and perhaps to forecast where it might be headed next. But pest experts aren't the only ones interested in mathematical studies of the way complex groups of living things move around. Daniel Grunbaum(ph), a researcher at the University of Washington, says fisherman, and ever crown control experts, know they can learn a lot.

Mr. DANIEL GRUNBAUM (Researcher, University of Washington): And then there are roboticists and people who are coming in from the engineering side who are very interested in figuring out how to make coordinated teams of robots do things.

NIELSEN: The common theme here is that a few simple rules can lead to all kinds of complex behaviors. Ian Cousins, of Princeton, cautions that there's still a lot that people don't know about locust swarms. For example, how do a billion flying insects change direction all at once? Maneuvers like these are why a locust swarm is unbelievably beautiful, he says, unless you happen to own the farm fields right in front of it. John Nielsen, NPR News, Washington. Transcript provided by NPR, Copyright National Public Radio.