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Did you know ... ? Locust swarms, serotonin and obesity

Until 1921, swarming locusts and solitary locusts were thought to be different species. After all, they look different and behave very differently. Then it was realised that something causes the solitary ones to overcome their mutual aversion and band together to fly long distances. But it was only in 2008 that the full picture emerged.

Professor Steve Simpson, of Sydney University, and collaborators at the universities of Oxford and Cambridge found that a growing shortage of protein in their diet drives the locusts further afield in search of more. All animals need protein, because the nitrogen in it is essential to building the body. Carbohydrates contain none, which explains why Simpson found that locusts would always choose protein-rich foods when offered a choice.

But locusts themselves are rich in protein, and are not fussy about who they eat. So to avoid being eaten, hungry solitary locusts will move to stay ahead of those behind.

In moving together in search of diminishing sources of protein, the locusts start bumping into one another. And this has a remarkable effect. Simpson and his colleagues found that simply tickling the hind legs of locusts for 2 hours to simulate this jostling is enough to turn the solitary creatures into a gregarious swarm.

Brain chemical

Their most recent work shows that the neurotransmitter (brain chemical) serotonin is responsible for this change. They found a short-lived rise in levels of serotonin in the locusts after the tickling. Further, giving the locusts serotonin or serotonin mimics triggered the transformation in solitary locusts, and giving them serotonin blockers prevented it even in crowded locusts.

This could lead to a new method of controlling swarms, although as all animals depend on serotonin, it will take some time to find a control specific to locusts.

Human diet

An offshoot of this work is the discovery that adequate protein may be key to preventing obesity in humans. Just as the locusts are now known to fill up until they reach a target protein level, it seems that we too might have the same mechanism. Our 21st century diet of fast food might be filling us up on high-carbohydrate, low-protein food, so we keep eating to satisfy the built-in protein drive. If we favour high-protein foods (such as meat and pulses), we might be able to reverse the growing obesity epidemic in the Western world.

Amazing what we can learn from insects.

Further reading

Anstey ML et al. Serotonin mediates behavioral gregarization underlying swarm formation in desert locusts. Science 323 (5914) 627–630. DOI: 10.1126/science.1165939: http://www.sciencemag.org/cgi/content/abstract/323/5914/627

Locusts help our understanding of human obesity: http://www.abc.net.au/catalyst/stories/s2069308.htm

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