Locust swarms are driven by salt and cannibalism

By Sally Palmer

Watch an exclusive video about locust swarms

LOCUSTS aren’t the kind of creatures that inspire much in the way of sympathy. In a bad year locust plagues can wreck the livelihoods of a tenth of the world’s population and cover a fifth of the land surface of the globe. Desert locusts (Schistocerca gregaria) – the most harmful species – have been a problem for millennia, munching their way across Africa, Asia and parts of Europe since the dawn of agriculture.

Yet the insects that make up these mass- migrating swarms may not be as hell-bent on destroying our agriculture as they seem. This month, a team of researchers reported that far from pushing relentlessly forward in search of crops, locusts are just as concerned with avoiding being eaten themselves (Current Biology, DOI: 10.1016/j.cub.2008.04.035). This insight could help stop them in their tracks even before they take to the skies.

Locusts are the most voracious of the grasshoppers. Unlike other grasshoppers, which lead solitary lives, under certain environmental conditions locusts band together in huge numbers and eat almost anything in their path. In the past hundred years, there have been eight particularly serious plagues of desert locusts, some of which have spanned several years (See Diagram). Yet despite more than 50 years of research, we still don’t know exactly what drives locusts to swarm and, more importantly, how to stop them.

Computer models of swarming, and of similar behaviours such as flocking in birds and shoaling in fish, have shown that individuals within a group adjust their speed and alignment in …