Mormon crickets will sometimes gather by the millions and crawl in bands stretching more than five miles long. Dr. Couzin and his colleagues ran experiments to find out what caused them to form bands. They found that the forces behind cricket swarms are very different from the ones that bring locusts together. When Mormon crickets cannot find enough salt and protein, they become cannibals.
“Each cricket itself is a perfectly balanced source of nutrition,” Dr. Couzin said. “So the crickets, every 17 seconds or so, try to attack other individuals. If you don’t move, you’re likely to be eaten.”
This collective movement causes the crickets to form vast swarms. “All these crickets are on a forced march,” Dr. Couzin said. “They’re trying to attack the crickets who are ahead, and they’re trying to avoid being eaten from behind.”