The desert locust is one of about a dozen species of grasshoppers known as locusts which - unlike other grasshoppers - are able to change their behaviour in response to population density. This enables them to form swarms that can migrate over large distances. Locust swarms vary from less than one square kilometre to several hundred square kilometres. There can be from 40 million to as many as 80 million locust adults in each square kilometre of a swarm.

More...