for National Geographic News
Mormon crickets, close relatives of locusts and grasshoppers, can devour their way across 50 miles (80 kilometers) of farmland in a single season.
Stephen Simpson, an entomologist at the University of Sydney in Australia, had long wondered why crop-eating bugs like Mormon crickets, which live in the western United States, cover so much ground so quickly.
He recently pinned down two driving forces, he says: a need for protein and a fear of cannibalism.
Simpson conducted a series of tests to determine what the crickets ate under different circumstances. The results showed that, when protein is scarce, Mormon crickets on the move are quick to devour each other.
This helps explain why the crickets showed a strong tendency to keep jumping forward, he says.
"They have an incentive to move, because they're least at risk of being cannibalized if they're going in the same direction as everybody else," Simpson said.
The result of this collective survival strategy is what Simpson dubs a "forced march."
Simpson reported his results yesterday in the Proceedings of the National Academy of Sciences.
Unusual Taste Test
Simpson noticed that Mormon crickets seemed very selective about what they ate, favoring seeds, other protein-rich plant partsand weaker members of their own species.
"They produce these massive bands moving across the landscape," Simpson said. "But they don't strip everything bare as they go. They'll leave food behind and go to the next field."
To get a clearer picture of the insects' nutritional needs, Simpson presented a test group of crickets with food-filled petri dishes. One held high-protein and low-carbohydrate food, another held high-carbohydrate and low-protein food, and a third had equal amounts of both.
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