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The ravenous swarm stretches as far as the eye can see.
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It has no commanding general or strategic plan;
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its only goals are to eat, breed, and move on—
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a relentless advance that transforms pastures and farms into barren wastelands.
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These are desert locusts— infamous among their locust cousins
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for their massive swarms and capacity for destruction.
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But these insects aren't always so insatiable.
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In fact, most of the time desert locusts are no more dangerous
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than garden-variety grasshoppers.
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So what does it take to turn these harmless insects
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into a crop-consuming plague?
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Desert locust eggs are laid in the damp depths of desert soil,
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in arid regions stretching from North Africa to South Asia.
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During the dry weather typical in these ecosystems,
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desert locusts live a solitary lifestyle.
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Adolescent hoppers will spend a few lonely weeks foraging for plants,
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before growing wings, reproducing, and dying.
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But when a region receives an abundance of rain,
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the scene is set for a startling transformation.
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Increased moisture supports more vegetation
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for newly hatched hoppers to eat,
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leading large groups to feed in close proximity.
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The frequent contact stimulates their leg hairs,
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triggering the release of a hormone
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that causes them to actively cluster even closer.
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Gluttonous crowds of locusts produce huge amounts of poop,
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which carries a pheromone that furthers their transformation.
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The hopper's diet shifts to include plants with toxic alkaloids.
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Soon, the locusts take on a striking pattern that warns predators
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of their newly poisonous nature.
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Smaller groups merge into bands of millions,
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which mow down virtually all plant life in a kilometer-wide swath.
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Roughly every week they shed and expand their exoskeletons,
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growing to roughly 50 times their hatching weight in just one month.
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Finally, the metamorphosis is complete.
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The adults beat their translucent wings and take flight
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as a full-fledged locust swarm.
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In this gregarious phase, these long-winged, brightly colored creatures
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appear so different from their solitary counterparts
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that they were long thought to be a separate species.
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A typical swarm contains more locusts than there are humans on the planet,
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covering hundreds of square kilometers in a dense cloud.
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At these numbers, desert locusts easily overwhelm their predators.
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A large swarm can match the daily food intake of a city of millions,
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and flying with the wind,
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the insect invasion can travel up to 150 kilometers a day.
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This living tornado can also cross large bodies of water.
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In 1988, a swarm even managed to traverse the Atlantic Ocean.
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The locusts likely formed rafts to rest at night,
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before fueling up in the morning with a nourishing breakfast of their dead kin.
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While flying over land, they seek out moist soil to lay eggs.
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Swarming mothers transfer their gregarious condition to their offspring,
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making it likely that the next generation will form another swarm.
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This means that while an individual desert locust lives only three months,
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a plague can last up to a decade.
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The potential for a years-long plague isn't unique to desert locusts,
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but the region they inhabit makes the prospect particularly deadly.
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Their habitat spans some of the world's poorest countries,
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largely populated by people who grow their own food.
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By consuming crops and pastures,
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these insects directly endanger 10% of humanity.
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Fortunately, a desert locust plague doesn't last forever.
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When a wet period ends,
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vegetation becomes scarce and egg laying conditions decline.
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As existing swarms die off, new hatchlings spread out in search of food,
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creating enough distance to prevent solitary locusts from transforming.
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Human intervention can also help.
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Researchers use satellite imagery to identify regions at risk
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of becoming locust hotspots and alert local governments.
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While most countries fight back with chemical insecticides,
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some regions have found success using fungal diseases that are lethal to locusts
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but safe for people and the environment.
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Unfortunately, other modern practices are exacerbating the threat.
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Fields densely packed with a single crop are like a table set for locusts.
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And erratic weather caused by climate change makes swarms harder to predict.
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If we plan to discourage lonely locusts from becoming catastrophic crowds,
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humans need to cut carbon emissions, rethink our agriculture,
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and generally reconsider our own ravenous appetites.