Migratory locust - 19th century wood engraving from THE WORLD OF WONDERS, 1892. Locust is the name given to the swarming phase of short-horned grasshoppers of the family Acrididae. The origins and apparent extinction of certain species of locust, some of which reach 6 inches (15 cm) in length are unclear. These are species that can breed rapidly under suitable conditions and subsequently become gregarious and migratory. They form bands as nymphs and swarms as adults both of which travel great distances during which they can strip fields rapidly and in so doing greatly damage crops. 固opFoto / Fortean