locust, in zoology, name for certain migratory members of the short-horned grasshopper family (Acrididae). Like other members of this family, locusts have antennae shorter than their bodies, song-producing organs on the forewings and hind legs, and hind legs well developed for jumping. Locusts lay their eggs in the ground; when the nymphs hatch they are wingless and move across the land by walking. Typical locusts (e.g., species of the Old World genus Locusta ) have two distinct adult forms, a short-winged migratory form and a long-winged nonmigratory form.
Locust migration is an occasional event, which follows an enormous buildup of a locust population. The young locusts, called nymphs, only develop into the migratory form under certain environmental conditions, which also lead to a population increase. Not all of the environmental factors involved are known, but one is hot weather. The first generation produced after a migration is not usually migratory.
When migration occurs the locust swarms are so dense as to blacken the sky over an area of many miles. When the insects finally settle, after traveling hundreds or thousands of miles, they begin to feed, consuming enormous quantities of vegetation. Locusts are serious agricultural pests. Spraying with solutions of arsenic and overturning the soil can destroy the eggs.
Locusts are most common in Africa and Asia, but also occur in the United States. The Rocky Mountain locust, Melanopolus spretus, a species that is now apparently extinct, destroyed millions of dollars worth of crops on the Great Plains between 1874 and 1877. A single swarm contained an estimated 124 billion insects. Cicadas are sometimes called locusts in the United States but are related to aphids and leafhoppers, not grasshoppers.
Locusts are classified in the phylum Arthropoda, class Insecta, order Orthoptera, suborder Caelifera, family Acrididae.