Strange Behavior Turns Crickets into Cannibals

Millions of Mormon crickets are on the move again in the Western United States, devouring everything in their path as they march in unison across wide swaths of land from Idaho to Oregon.

If you're a farmer, it's an invasion from hell.

But if you're a Mormon cricket, the farmers have it easy. The farmers aren't facing starvation, and they're not likely to get eaten by other members of their family. But that's what it's like this time of the year for the insects, according to new research that explains why they engage in behaviors that are unusual, even for insects.

It turns out that the insects form huge "bands" to protect themselves from predators, and they march across the countryside in a desperate search for protein, according to Patrick Lorch, an insect behaviorist at Kent State University. Although their wings are too feeble for them to fly, they can move more than a mile in a single day, driven partly by a fear of cannibalism.

Lorch is one of many scientists who have tried to figure out why Mormon crickets, which aren't really crickets (they're katydids) behave the way they do. In the high country, like the Rockies, they act like they are supposed to act, eating other insects, mating and staying pretty much to themselves.

But in the sagebrush-covered plains, it's a different story. They sometimes form huge bands, numbering in the millions, with more than 100 crickets per square yard. And for reasons that have long puzzled scientists, they march in one direction, climbing over everything in their paths, devouring crops and creating a huge splatter of goo whenever they cross a highway.

Why do they do that? Lorch and several other scientists addressed that question while he was a postdoctoral researcher at the University of North Carolina at Chapel Hill. They actually attached tiny radio transmitters to the backs of some of the crickets so they could monitor their behavior.

The crickets are pretty large, measuring up to 2 inches long, but they weigh only about half as much as a nickel, so even a tiny transmitter was a heavy load. But it paid off, at least for the scientists.

"We know why they form these groups," Lorch said. Protein is very scarce in the rangeland of the far West, so "everybody out there is looking for protein." And of course insects, which need protein, are also a source of protein.

"So all the little lizards and rodents and mice are hammering them when they are by themselves." The crickets apparently figured out that there's strength in numbers, and survival could best be achieved by banding together.

"If you're in a dense group, and if you're in the middle of the group, you're safe," Lorch says. Predators may nibble around the edges, but they're less likely to pick off those crickets that are surrounded by their colleagues.

But why do they move out en masse?

"It looks like protein starvation is what's driving them," Lorch says. "You want to be out in front of everybody else because you want to get whatever food is available. And you don't want to get eaten by the guys in the back who may not get anything, other than you. So there's this doubled-edged thing where you want to get out in front because you want to get the food, and at the same time there's cannibalism happening at really high rates. So that makes the band move."

Lorch, who started studying Mormon crickets because he was interested in their sex lives, says even their mating changes dramatically in a protein-deficient environment.

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