Fear of cannibalism causes locusts to swarm, scientists have discovered

Locust swarms that have plagued desert regions of the world since biblical times are driven by cannibalism, scientists believe.

The spectacular destructive behaviour of the large voracious grasshoppers has long puzzled experts.

Black clouds of the insects up to 10 billion strong can cover an area as large as greater London, stripping fields of crops bare and leaving starvation and economic ruin in their wake. A large swarm may eat 160,000 tonnes of food each day.

No-one has adequately been able to explain what triggers the locust feeding frenzy. But new research by experts from the US, UK and Australia suggests that the creatures swarm because they are hungry - for each other.

Although desert locusts usually feed on vegetation, cannibalistic behaviour has been observed in individual insects. Young flightless locusts resort to eating other members of their group when normal food supplies start to run short, say the scientists.

Starved of essential nutrients such as protein and salt, locust nymphs will nip at each other. According to the theory, a kind of panic sets in as some insects try to escape from their more aggressive neighbours.

A build up of activity follows with large numbers of locusts moving forward in an attempt to get away from the hungry cannibals approaching from behind.

The researchers came to their conclusions after closely studying locust nymphs and using a computerised motion analysis system to track the insects marching in an enclosed area.

Study leader Dr Iain Couzin, from Princeton University in New Jersey, US, said: "Once they take flight, locust control is extremely expensive and ineffective. So understanding when, where and why the bands of juvenile locusts form is crucial for controlling locust populations."

The research is published in the May online edition of the journal Current Biology.