Scientists have discovered the chemical signal that triggers the transformation of locusts from antisocial insects into monstrous swarms.

Scientists from Oxford University, Cambridge University and Sydney University monitored the behaviour of locusts. They have discovered the trigger is serotonin, a chemical which anti-depressant drugs aim to keep at a high level in humans.

“The question of how locusts transform their behaviour in this way has puzzled scientists for almost 90 years,” said co-author Dr Michael Anstey, from Oxford University, “Now we finally have the evidence to provide an answer.”