Desert locust

The desert locust can be in a solitarious phase at low density; with crowding and suitable conditions its behaviour and appearance may shift towards the gregarious phase, and swarms form.

When desert locusts increase in number and become more crowded, their behaviour changes from individual behaviour (the solitarious phase) to group behaviour (the gregarious phase); until 1921 the two were thought to be different species. Solitary adults usually fly at night, while swarms fly by day with the wind at 16–19 km/h and may cover 5–130 km or more in a day, and one square kilometre of swarm contains 40 to 80 million adult locusts.