A tenth of the planet’s population occasionally suffers through devastating famines because small insects fear being bitten in the bum. That’s the astonishing message from a new study of one of mankind’s greatest pests – the desert locust.

Swarms can stretch for several hundred square kilometres and each of these harbours up to 80 million hungry sets of mandibles that eat their own body weight in food every day. These plagues are unpredictable but they only form when locust populations reach some sort of critical mass. Desert locusts are two insects for the price of one; at a crowded tipping point, they transform from loners (which are green or brown) into more sociable forms that are red or yellow and