Locust

Locusts are certain species of short-horned grasshoppers, most notably the migratory locust, Locusta migratoria, that display an extraordinary trait called phase polyphenism: under normal, low-density conditions they behave as ordinary solitary grasshoppers, but when populations become crowded, they undergo physical and behavioral changes into a gregarious swarming form. This transformation can produce enormous, coordinated swarms capable of traveling long distances and consuming vast quantities of vegetation.

Solitary-phase locusts are typically green or brown and blend into vegetation much like other grasshoppers, while gregarious-phase individuals often develop brighter, more contrasting coloration along with proportionally longer wings suited to sustained group flight. This phase change, triggered by tactile and chemical cues from increased population density, is one of the most striking examples of environmentally induced variation known in insects.

Historically, locust swarms have had major agricultural and economic impacts across Africa, Asia, and parts of Europe, and outbreaks continue to be monitored closely by agricultural authorities in affected regions today.

• Large grasshopper, 35–55 mm long, with powerful jumping hind legs
• Solitary phase is typically green or brown, camouflaged against vegetation
• Gregarious swarming phase often shows brighter yellow, orange, or pinkish tones
• Long, well-developed wings capable of sustained flight, especially in the swarming phase
• Lookalikes: many non-swarming grasshoppers appear similar in solitary phase; behavior and population density are key distinguishing factors

Locust species occupy open grasslands, savannas, floodplains, and agricultural regions across Africa, the Middle East, Asia, southern Europe, and Australia, depending on the species. Outbreak areas often correspond to regions with variable rainfall, where periods of drought followed by vegetation growth create conditions favorable for population buildup and subsequent swarming.

In the solitary phase, locusts behave much like ordinary grasshoppers, feeding individually on grasses and other vegetation and avoiding close contact with others of their kind. When conditions allow populations to grow dense, increased physical contact triggers a shift to the gregarious phase, in which individuals actively seek out others, form marching bands as nymphs, and later take to the air as coordinated adult swarms that can travel long distances in search of food. Swarms are voracious herbivores capable of stripping vegetation over large areas, making locust outbreaks historically significant events for agriculture and rural food security.

Females lay egg pods in the soil, each containing dozens of eggs protected by a frothy secretion that hardens around them. Nymphs, called hoppers, hatch wingless and pass through five to six molts, growing progressively larger and, under crowded conditions, developing the gregarious phase coloration and marching behavior even before reaching adulthood. After a final molt, winged adults emerge and, depending on population density, either disperse individually or join swarms; multiple generations can occur in a year in warm climates, with outbreak cycles sometimes spanning several years between major swarming events.