MILLIONS of insects are forced to march across great swathes of western North America each year. They are driven not just by terrible hunger but also by the merciless cannibal jaws of their comrades.
Unfortunately for Mormon crickets, this is not an invertebrate horror movie, it is real life. When they march together, they can move up to 2 kilometres a day, driven by the need for food and salt. The insect army can cause serious crop damage, but unlike locusts they don鈥檛 devour all the plants in their path.
Curious as to whether nutritional requirements could explain this behaviour, Stephen Simpson of the University of Sydney, Australia, and Greg Sword of the US Department of Agriculture鈥檚 research service placed foods rich in either proteins or carbohydrates in the path of the marching insects. The crickets showed a clear preference for the protein-rich food (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.0508915103).
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The insects swarm when there isn鈥檛 enough protein to go around, and that鈥檚 when the cannibalism starts. 鈥淢ormon crickets are walking packages of protein and salt,鈥� says Simpson. Cannibalism is common, and any insect that stops to eat risks being eaten itself.
