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.
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 can travel great distances, rapidly stripping fields and greatly damaging crops.
Though the female and the male look alike, they can be distinguished by looking at the end of their abdomen. The male has a boat-shaped tip while the female has two serrated valves that can be either apart or kept together. These valves aid in the digging of the hole in which an egg pod is deposited.
Doris Lessing, the British writer who won the Nobel Prize for Literature for the year 2007, vividly described a locust attack in her short story titled "A Mild Attack of Locusts". The story, published in the February 26 1955 issue of The New Yorker, is set in the South African countryside and describes how a family of farmers attempts to resist the attack, to prevent and minimize the damage and to come to terms with the loss of crops.
In Lonesome Dove by Larry McMurtry, the cow herd experiences being in the path of a swarm of locusts whose passage lasts several hours and which strips the prairie grass around them down to the nub, and even chews on the cowboys' clothing.
Research at Oxford University has identified that swarming behaviour is a response to overcrowding. Increased tactile stimulation of the hind legs the locust will then cause it to start to become stressed, start to eat much more, and breed much more easily. The transformation of the locust to the swarming variety is induced by several contacts per minute over a four-hour period. It is estimated that the largest swarms have covered hundreds of square miles and consisted of many billions of locusts.
The extinction of the Rocky Mountain locust has been a source of puzzlement. Recent research suggests that the breeding grounds of this insect in the valleys of the Rocky Mountains came under sustained agricultural development during the large influx of gold miners, destroying the underground eggs of the locust. .
The use of "locust" in English as a synonym for "lobster" has no grounding in anglophone tradition, and most modern instances of its use are usually calques of foreign expressions (e.g. "sea locust" as mistranslation of langouste de mer). There are, however, various species of crustaceans whose regional names include the word "locust." Thenus orientalis, for example, is sometimes referred to as the Flathead locust lobster (its French name, Cigale raquette, literally "raquet cicada," is yet another instance of the locust-cicada-lobster nomenclatural connection). Similarly, certain types of amphibians and birds are sometimes called "false locusts" in imitation of the Greek pseud(o)acris, a scientific name sometimes given to a species because of its perceived cricket-like chirping. Often the linguistic non-differentiation of animals that not only are regarded by science as different species, but that often exist in radically different environments, is the result of culturally perceived similarities between organisms, as well as of abstract associations formed within a particular group's mythology and folklore (see Cicada mythology). On a linguistic level, these cases also exemplify an extensively documented tendency, in many languages, towards conservatism and economy in neologization, with some languages historically only allowing for the expansion of meaning within already existing word-forms. Also of note is the fact that all three so-called locusts (the grasshopper, the cicada, and the lobster) have been a traditional source of food for various peoples around the world (see entomophagy).
The word "locust" has, at times, been employed controversially in English translations of Ancient Greek and Latin natural histories, as well as of Hebrew and Greek Bibles; such ambiguous renderings prompted the 17th-century polymath Thomas Browne to include in the Fifth Book of his Pseudodoxia Epidemica an essay entitled Of the Picture of a Grasshopper, it begins:
There is also among us a common description and picture of a Grashopper, as may be observed in the pictures of Emblematists, in the coats of several families, and as the word Cicada is usually translated in Dictionaries. Wherein to speak strictly, if by this word Grashopper, we understand that animal which is implied by τέτιξ with the Greeks, and by Cicada with the Latines; we may with safety affirm the picture is widely mistaken, and that for ought enquiry can inform, there is no such insect in England.Browne revisited the controversy in his Miscellany Tracts (1684), wherein he takes pains (even citing Aristotle's Animalia) to both indicate the relationship of locusts to grasshoppers and to affirm their like disparateness from cicadas:
That which we commonly call a Grashopper, and the French Saulterelle being one kind of Locust, so rendered in the plague of Ægypt, and in old Saxon named Gersthop.Compound words involving "locust" have also been used by anglophone translators as calques of archaic Arabic, Greek, Hebrew, or other language names for animals; the resulting formations have, just as in the case of the Brownian grasshopper/cicada controversy, been, at times, a cause of lexical ambiguity and false polysemy in English. An instance of this appears in a translation of Pliny included in J.W. McCrindle's book Ancient India as Described in Classical Literature, where an Indian gem is said by the Roman historian to have a "surface [that] is even redder than the shells of the sea-locust.