It sounds like the makings of a creepy movie. Swarms of crickets band together and march across the landscape. They crawl over everything in their path, and they make an eerie rustling sound as they move. Along the way, they eat each other when they get the chance.

The phenomenon is strange, but true. A new set of studies offers an explanation for why it happens: Crickets go on the march when they're short of protein and salt in their diets. As a group, they search for more nutritious pastures. Those crickets that can't move as quickly as others do get eaten by their fellows.

 

 

 

Mormon crickets are normally mellow creatures. They eat alone or in small groups. The insects can't fly, but they can walk or hop.

Every once in a while, however, several million of the insects get together and form into a broad column that can be up to 10 kilometers long. The column then moves at a rate of about 2 kilometers per day.

Scientists suspected that the marching crickets are looking for food. To decode the behavior, the researchers first offered several varieties of dry food to swarms of crickets in the wild. Protein-rich food got the most attention, as crickets aggressively lunged and pushed to get at it. They didn't care much for high-carbohydrate mixes.

In another test, crickets crowded around cotton wool that had been soaked in saltwater. They left salt-free versions alone.

Laboratory experiments confirmed these findings. There, crickets that could eat whatever they wanted went first for salty, protein-rich foods. After a day or two, they went for other stuff.

It turns out that Mormon cricket bodies are actually full of salt and protein, too, which can make them an appealing snack for one another. The scientists found that crickets that didn't move as quickly as others moved or had already died often ended up in the stomachs of their companions.

Food cravings can be a powerful motivating force.