Millions of Mormon crickets swarm across western North America—not to devour crops, as do the more familiar locust hordes, but apparently to flee from one another. An international team studying a one-kilometer-long swarm in Idaho last year found that the flightless crickets were avid cannibals. When the scientists left food out for the insects, they clearly preferred meals high in protein and salt, nutrients the crickets are themselves rich in. Impairing cricket mobility (by gluing them to rocks) substantially increased the risk of cannibalization, suggesting that the insects swarm to escape death from behind. Although these forced marches are obviously dangerous for the crickets, apparently traveling alone is even more so, often quickly leading to death from predation. These findings, published online March 3 in the Proceedings of the National Academy of Sciences USA, could elucidate why locusts and other insects swarm.