Out of Africa

From Africa, they probably migrated to the western hemisphere three to five million years ago by hitching a ride on the prevailing easterly winds and flew westward across the Atlantic Ocean.

On its own, a desert locust is pretty harmless. It's when you get a group of them together that you have trouble.

"Normally, they are solitary creatures," said study author Sean Mullen of the University of Maryland. "But when they become densely populated, they become gregarious. They actually go through developmental and behavioral changes because of the physical contact."

First they change from a soft green color to a more ominous dark brown and yellow. Then they cluster into groups of millions--or even billions--and create a swarm that can block the sun. However, most of the western hemisphere species do much less damage than the desert locust and rarely form large swarms.

This research is detailed in the January issue of the journal The Proceedings of the Royal Society of London.