Locusts are related to grasshoppers and the two insects look similar. However, locust behavior can be something else entirely. Locusts are sometimes solitary insects with lifestyles much like grasshoppers. But locusts have another behavioral phase called the gregarious phase. When environmental conditions produce many green plants and promote breeding, locusts can congregate into thick, mobile, ravenous swarms.
Locust swarms devastate crops and cause major agricultural damage and attendant human misery—famine and starvation. They occur in many parts of the world, but today locusts are most destructive in sustenance farming regions of Africa.
The desert locust is notorious. Found in Africa, the Middle East, and Asia, they inhabit some 60 countries and can cover one-fifth of Earth’s land surface. Desert locust plagues may threaten the economic livelihood of one-tenth of the world’s humans.
A desert locust swarm can be 460 square miles (1,200 square kilometers) in size and pack between 40 and 80 million locusts into less than half a square mile (one square kilometer).
Each locust can eat its weight in plants each day, so a swarm of such size would eat 423 million pounds (192 million kilograms) of plants every day.
Like the individual animals within them, locust swarms are typically in motion and can cover vast distances. In 1954, a swarm flew from northwest Africa to Great Britain. In 1988, another made the lengthy trek from West Africa to the Caribbean. From http://animals.nationalgeographic.com/animals/bugs/locust/