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If you take anti-depressants, you might be interested in some new research on locusts. That's right, locusts, these swarming grasshoppers that have plagued farmers since biblical times. Scientists say that they have found the chemical trigger that makes locusts gather together and it's the same brain chemical affected by Prozac. NPR's Nell Greenfieldboyce has more.

NELL GREENFIELDBOYCE: A swarm of locusts can have billions of insects and stretch for miles. Back in 2004, my NPR colleague, Richard Harris, went to West Africa and stepped out of his car into a cloud of the big bugs. Listen closely.

(Soundbite of locusts swarming in West Africa)

RICHARD HARRIS: They carpet a rice field and an adjoining pasture, and they even land on our clothes. Locusts don't vocalize, but we hear their wings and we hear the sound they make as they eat these plants down to their bare stems.

GREENFIELDBOYCE: This kind of voracious swarm is why locusts are famous. But, it's actually not their usual routine.

Professor STEVE ROGERS (Zoology, University of Cambridge, England): The swarming is something the locusts only do very occasionally.

GREENFIELDBOYCE: Steve Rogers studies locusts at the University of Cambridge in England.

Prof. ROGERS: The fact locusts can spend many generations in a form that not only doesn't swarm, but is actively repelled by the other locusts.

GREENFIELDBOYCE: He says locusts are usually solitary creatures, just harmless mild-mannered grasshoppers. But, if something like a drought forces locust to crowd together at a dwindling food source, and they start to smell and see other locusts and touch them...

Prof. ROGERS: This is the exactly the point to which behavior changes dramatically.

GREENFIELDBOYCE: The locusts go through a Dr. Jekyll and Mr. Hyde kind of transformation. They become gregarious. They seek out others so they can migrate as a group. Roger says this change happens quickly after just a few hours of forced crowding. He and his colleagues wanted to know what was actually happening inside the insect to cause such a dramatic change.

First, they found that inside insect's nervous system there was steep rise in a brain chemical called serotonin. But was this causing the change? Michael Anstey is a researcher at the University of Oxford. He says they decided to find out and this week, in the Journal Science, they report on what happened when they gave locusts drugs that alter serotonin levels.

Mr. MICHAEL ANSTEY (Zoology, University of Oxford): You know, it was absolutely startling to see the effect that these drugs had.

GREENFIELDBOYCE: He says drugs that block serotonin made solitary locusts stay shy, they never became gregarious, even in conditions that would normally make them swarm.

Mr. ANSTEY: This really was the Eureka moment.

GREENFIELDBOYCE: And drugs that boosted serotonin made solitary locust be suddenly attracted to other insects.

Mr. ANTSEY: Watching those locusts actually go and behave as if they'd been in a crowd, or were born in a crowd, is absolutely remarkable. So, it's quite exciting and truly - truly fun to do.

GREENFIELDBOYCE: Besides being fun, researchers hope this new insight might lead to new forms of pest control. That's a long way off. But Steve Roger says it is surprising to see just a single chemical making such a difference.

Prof. ROGERS: Using models like these in wasps, we know that as they change behavior, as they leave the nest and things, there is a whole stew of different chemical changes going on. So the thing that we found is generally quite unusual.

GREENFIELDBOYCE: Still, serotonin is known to affect behavior in other species, and boosting serotonin is what drugs like Prozac do.

Mr. ROGERS: Serotonin is implicated in a lot of aspects of mood and well-being in humans as well as causing this change in locusts.

GREENFIELDBOYCE: A solitary locust may seem far removed from a depressed person, but Roger says at a very, very deep level there may be some interesting similarities. Nell Greenfieldboyce, NPR News.

(Soundbite of music)

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