Locusts periodically cause natural disasters in several parts of the world. When the locust population density is low the locusts behave as individuals. However, when the population density increases locusts form highly mobile swarms. The change from solitary to gregarious is generally accompanied by changes in body shape and colour. In Australia locust plagues occur when widespread inland areas receive good rainfall in successive seasons.
High rainfall stimulates the growth of grass which creates an ideal habitat for locust breeding.
The timing of the rainfall is important. If wet seasons continue the swarming phase is prolonged. A series of dry seasons is necessary for the locust population numbers to decrease thus stimulating the change to the solitary form of the insect. Locusts are vegetarians. As they swarm and migrate they devastate grasslands and crops in the areas they pass through.