Common chemical causes locusts to swarm (AP)

Undated photo provided by the journal Science shows side views of desert locust. On left, gragarious stage in which they swarm and devastate crops and on right, solitary stage in which locusts avoid one another. (AP Photo/Science, Tom Farle)AP - A chemical that affects people's moods also can transform easygoing desert locusts into terrifying swarms that ravage the countryside, scientists report. "Here we have a solitary and lonely creature, the desert locust. But just give them a little serotonin, and they go and join a gang," observed Malcolm Burrows of the University of Cambridge in England.