seventeen-year locust: see cicada.

locust, in botany, any species of the genus Robinia, deciduous trees or shrubs of the family Leguminosae (pulse family) native to the United States and Mexico. The locusts have pendent clusters of flowers similar to the sweet pea; these are very fragrant in the black, or yellow, locust (R. pseudoacacia), which is the common locust, sometimes also called acacia, or false acacia. This species has been widely planted in the past for ornamental purposes, for erosion control, and for its useful wood, but the locust borer has killed it in many areas. Its heavy, hard, durable wood has been used extensively for treenails in shipbuilding, for fence posts, for turning, and for fuel. The shoots and bark of the black locust are poisonous. The honey locust belongs to a different genus of this family, as does the carob, which is thought to have been the biblical locust. Locust is classified in the division Magnoliophyta, class Magnoliopsida, order Rosales, family Leguminosae.

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.

honey locust, leguminous deciduous tree (Gleditsia triacanthos) of the family Leguminosae (pulse family), native to the eastern half of the United States but planted as a shade tree in many regions of the United States and in other countries, where it is sometimes naturalized. It has heavily fragrant flowers attractive to bees, compound leaves made up of small leaflets, and large branching thorns. The pods, which usually twist with age, are brown, flat, about 12 to 18 in. (30.5-45.7 cm) long, and have a sweet, edible pulp that has been used to make beer. Pulp of Asian species has substituted for soap. Wood of the honey locust is durable and has been used chiefly for fence posts and crossties. A thornless variety is widely planted in the N United States as a street tree. Other trees called locust belong to the same family. The honey locust is classified in the division Magnoliophyta, class Magnoliopsida, order Rosales, family Leguminosae.

black locust: see locust.

Any of several species of grasshoppers (family Acrididae) that undergo population explosions and migrate long distances in destructive swarms. In North America the names locust and grasshopper are interchangeable and used for any acridid; cicadas are sometimes called locusts. In Europe locust refers to large species and grasshopper to small ones. Locusts are found worldwide. Sporadic locust swarms may be explained by the theory that swarming species have a solitary phase (the normal state) and a gregarious phase. Nymphs that mature in the presence of many other locusts develop into the gregarious type; thus migratory swarms form as a result of overcrowding. Swarms may be almost unimaginably large, towering 5,000 ft (1,500 m) high; in 1889 a Red Sea swarm was estimated to cover 2,000 sq mi (5,000 sq km). Locust plagues can be extremely destructive of crops.

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