Locusts are the swarming phase of certain species of short-horned grasshoppers in the family Acrididae. These are species that can breed rapidly under suitable conditions and subsequently become gregarious and migratory when their populations become dense enough. They form bands as nymphs and swarms as adults. Both the bands and the swarms are nomadic and rapidly strip fields and greatly damage crops. The adults are powerful fliers; they can travel great distances, consuming practically all green material wherever the swarm settles.

The origin and apparent extinction of certain species of locust—some of which grew to 6 inches (15 cm) in length—are unclear.

Locusts are edible insects and are considered a delicacy in some countries. There have been references to their consumption as food throughout history. On swarming they are known to produce a toxin that renders them inedible and causes a skin reaction in sunlight.