Locust
Swarming grasshoppers that form plagues since prehistory.
Locusts are the swarming phase of certain species of short-horned grasshoppers in the family Acrididae. These insects are usually solitary, but under certain circumstances they become more abundant and change their behaviour and habits, becoming gregarious. No taxonomic distinction is made between locust and grasshopper species; the basis for the definition is whether a species forms swarms under intermittently suitable conditions. Locusts have formed plagues since prehistory, devastating crops and causing famines and human migrations.
- field
- Entomology
- known_for
- Swarming phase of short-horned grasshoppers that form plagues
- species_examples
- Desert locust (Schistocerca gregaria), Migratory locust (Locusta migratoria), Australian plague locust (Chortoicetes terminifera)
Lore & Background
Locusts are various species of short-horned grasshoppers in the family Acrididae that have a swarming phase. Normally innocuous and low in numbers, under suitable conditions of drought followed by rapid vegetation growth, serotonin in their brains triggers dramatic changes: they start to breed abundantly, becoming gregarious and nomadic. They form bands of wingless nymphs that later become swarms of winged adults, which rapidly strip fields and damage crops. The adults are powerful fliers and can travel great distances, consuming most green vegetation wherever the swarm settles. The change is described as density-dependent phenotypic plasticity, first analyzed by Boris Uvarov, who designated the two phases as solitaria and gregaria. Swarming behaviour is a response to overcrowding; increased tactile stimulation of the hind legs causes an increase in serotonin levels, leading to changes in colour, eating, and breeding. The formation of initial bands is called an outbreak; when these join into larger groups, it is known as an upsurge; continuing agglomerations on a regional level are known as plagues.
Reader's Guide
Locusts have been a significant historical force, mentioned in ancient texts such as the Iliad, the Mahabharata, the Bible, and the Quran, and carved on Egyptian tombs. Their swarms have caused famines and human migrations. In modern times, changes in agricultural practices and better surveillance of breeding grounds have allowed control measures at an early stage. Traditional control uses insecticides from ground or air, but newer biological control methods are proving effective. Despite modern surveillance, swarms can still form when suitable weather conditions occur and vigilance lapses. Locusts are also large insects convenient for research and classroom study, and are edible by humans, having been eaten throughout history and considered a delicacy in many countries.
Did You Know?
- Locusts are derived from the Latin locusta, meaning locust or lobster.
- Swarming has evolved independently in multiple lineages, comprising at least 18 genera in 5 different subfamilies.
- A large swarm can consist of billions of locusts spread over thousands of square kilometres, with up to 80 million per square kilometre.
- Swarm-migration behaviour in juvenile desert locusts is partially mediated by cannibalistic interactions between individuals.
Frequently Asked Questions
What exactly is a locust?
A locust is not a distinct species but the swarming phase of certain short-horned grasshoppers in the family Acrididae. These insects are normally solitary, yet when crowding and other triggers align they shift into a gregarious, group-living mode that defines the locust state.
What makes locusts so destructive?
In their gregarious phase, locusts assemble into enormous swarms capable of stripping vegetation across vast regions, wrecking agricultural crops in a matter of days. This plague behavior has been documented since prehistory and has repeatedly triggered famines and mass human migrations.
How is a locust different from a regular grasshopper?
There is no taxonomic boundary between the two; the very same species can exist as a solitary grasshopper or as a swarming locust depending on environmental conditions. The distinction is purely behavioral, hinging on whether the individual is part of a dense, gregarious group or lives in isolation.
Which species are the most famous locusts?
The Desert locust (Schistocerca gregaria) is the best-known example, followed by the Migratory locust (Locusta migratoria) and the Australian plague locust (Chortoicetes terminifera). All three are Acrididae members that can form the catastrophic swarms the term 'locust' implies.
Why do locusts matter to entomology and human history?
Locusts are a prime model for studying phase polyphenism, where a single genotype produces drastically different behaviors under shifting conditions. Their plagues have shaped human civilization, driving the development of pest-control strategies and influencing settlement patterns across multiple continents.
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