What is a locust?

Photo by Brandon Woo

A locust is a unique type of grasshopper (Orthoptera: Acrididae) that can form dense migrating groups as juvenile marching bands or adult flying swarms. They have strikingly different phenotypic forms, or "phases". A solitarious phase occurs in low population densities, where the locust is shy and well camouflaged, behaving like a "typical" grasshopper. The gregarious phase happens under crowded conditions and is characterized by color changes, aggregation, and swarming behavior. Scientists call this ability of locusts to change phases “phase polyphenism”, an extreme type of phenotypic plasticity. It is in the gregarious phase that locusts become a food security concern, with their ability to migrate long distances and eat their own body weight in food each day, cumulatively these many millions of hungry insects can decimate agricultural and pasture land with very little warning. Of approximately 12,000 grasshopper species, fewer than 20 are considered locusts. Swarming behavior in locusts has independently evolved multiple times around the world, indicating that ecological factors have repeatedly favored the evolution of locusts from their grasshopper ancestors.

Relevant articles

• Glossary
• Evolution, behavior, and physiology of locust phase polyphenism
• Locust ecology
• Primer on locust and grasshopper management
• Biopesticides
• Edible insects and locusts as more than pests

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  Desert locust swarm in Kenya ©FAO/Sven Torfinn
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  A swarm of desert locusts in Somaliland ©FAO/Isak Amin
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  Sean McCann desert locust 2011
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  Desert locust outbreak 2020 ©FAO/Sven Torfinn

Why are locusts an agricultural problem?

A locust outbreak could consist of nearly 100 billion ravenous insects. Such a swarm could cover around 500 square miles or 258 hectares. Additionally, an adult locust has the capacity to consume its own weight in food every day. Compare that to a person trying to do the same to get a perspective of this remarkable feat. The voracious appetite of locusts poses a formidable threat to vegetation, potentially resulting in the devastation of crops and pasture land. In a single day, an amassed swarm of locusts can consume a staggering 423 million pounds of plant matter. Once all the plants are gone, the locusts proceed en masse to the next location, leaving a devastated landscape in their wake.

During outbreak years, locusts have been known to blanket up to one-fifth of the Earth's total land area. In such circumstances, approximately one out of every ten individuals worldwide is adversely affected.

What causes a locust outbreak?

Abundant rainfall is usually the key component that drives a locust outbreak. Precipitation provides the necessary moisture for egg-laying, while subsequent heat facilitates hatching and thriving of young locusts. Concurrently, vegetation grows and offers an ample food supply for the burgeoning locust population. This surge in plant life supports rapid reproduction, further exacerbating the situation. Additionally, locusts exist in two distinct phases: the solitarious phase, characterized by solitary behavior, and the gregarious phase, when they form swarms. Crowding and competition for food can trigger a transition from the solitarious to the gregarious phase, culminating in the formation of large, migratory swarms.

Wind patterns can also serve as a pivotal factor in outbreaks. Strong winds carry locusts over extensive distances, facilitating their migration to new regions in search of food. This sudden influx of swarms in previously unaffected areas is a hallmark of locust outbreaks. Climate change and climate anomalies, such as El Niño and La Niña events, can also impact precipitation levels and vegetation growth, influencing locust dynamics.

Human activities like heavy livestock grazing, deforestation, soil degradation, and changes in land use can create environments more conducive to locust breeding and survival.

Read more about locust ecology here.

Frequently asked questions

The Commission for Controlling the Desert Locust in the Central Region (CRC)
FAO Desert Locust Watch Frequently Asked Questions (FAQs) about locusts
FAO Desert Locust Q&A
Q&A: The impact of desert locusts in the Horn and Eastern Africa
The World Bank
National Geographic FAQs

Learn from select educational media articles

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  Learn more about locusts and what makes them swarm
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  A swarm of desert locusts in Somaliland ©FAO/Isak Amin
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  The Strange Thing That Turns Grasshoppers Into Locusts, Bizarre Beasts 2022
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  A locust plague hit East Africa. The pesticide solution may have dire consequences, National Geographic 2021

Learn about locusts from select media articles
Learn about locust pop culture