Stephen J. Simpson and colleagues have a gory story to tell (Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0508915103; 2006). They investigated the factors that contribute to the mass movements of flightless Mormon crickets (Anabrus simplex), which inhabit western North America. Under certain conditions, these insects form into marching bands millions strong and several kilometres in length, and can walk up to 2 kilometres a day.
From their studies, Simpson et al. conclude that group movement is driven not only by ‘pull’ from in front, in the form of the search for specific nutrients (protein and salt), but by ‘push’ from behind — cannibalism. The crickets are themselves “walking packages of protein and salt”. So unless an individual is in the forefront of the band as it rolls into new territory, its only recourse to satisfy its dietary needs may well be to make a meal of a fellow traveller. As this picture shows, Mormon crickets have a taste for their own. It was taken near Reno, Nevada, and shows one unfortunate individual, killed by a car, being consumed by another cricket (a phenomenon that sometimes occurs on a mass scale).
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