A vast, densely packed aggregation of migratory locusts that forms when normally solitary grasshopper-like insects undergo a behavioral and physical transformation triggered by crowding, becoming more social and mobile as their population density rises after favorable breeding conditions. A large swarm can contain many billions of insects, and historically, and still today in parts of Africa, the Middle East and South Asia, locust swarms have caused famine-level crop destruction across vast areas.
Facts
PeriodicityOutbreaks recur irregularly; since the early 1960s there have been two major desert locust plagues (1967-1968 and 1986-1989) and six smaller upsurges. 1 ScaleA single swarm can cover up to 1,200 square kilometres and contain between 40 and 80 million locusts per square kilometre. 1 First DescribedThe phase theory explaining how crowding transforms solitary locusts into swarming gregarious locusts was first published by Boris Uvarov in 1921. 2 Identification
Distinguishing AppearanceGregarious-phase hoppers develop bold black markings on a yellow background, unlike the greenish or brownish camouflage coloring of the solitary phase. 1 Connections
Associated With
Desert locust plagues are documented to follow the end of extended drought, when the heavy rains that break a drought create the moist soil conditions locusts need for mass breeding and swarm formation.
Sources
1. Desert Locust (Wikipedia)
Wikimedia Foundation1960s to present section
Since the early 1960s, there have been two desert locust plagues (1967-1968 and 1986-1989) and six desert locust upsurges (1972-1974, 1992-1994, 1994-1996, 2004-2005, 1996-1998, and 2019-2021).
Ecology and swarming section
A single swarm can cover up to 1,200 square kilometres (460 sq mi) and can contain between 40 and 80 million locusts per square kilometre (100,000,000 and 210,000,000 per square mile) (a total of around 50 to 100 billion locusts per swarm, representing 100,000 to 200,000 metric tons (98,000 to 197,000 long tons; 110,000 to 220,000 short tons), considering an average mass of 2 g per locust).
Ecology and swarming section, paragraph on phase coloration
In the gregarious phase, the hoppers bunch together and in the later instars develop a bold colouring with black markings on a yellow background.
View the Source 2. Boris Uvarov - Wikipedia
Selected works sectionQuote, Selected works section
"A revision of the genus Locusta, L.(= Pachytylus, Fieb.), with a new theory as to the periodicity and migrations of locusts." Bulletin of entomological Research 12.2 (1921): 135-163.
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