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  • The ravenous swarm stretches as far as the eye can see.

  • It has no commanding general or strategic plan;

  • its only goals are to eat, breed, and move on

  • a relentless advance that transforms pastures and farms into barren wastelands.

  • These are desert locustsinfamous among their locust cousins

  • for their massive swarms and capacity for destruction.

  • But these insects aren't always so insatiable.

  • In fact, most of the time desert locusts are no more dangerous

  • than garden-variety grasshoppers.

  • So what does it take to turn these harmless insects

  • into a crop-consuming plague?

  • Desert locust eggs are laid in the damp depths of desert soil,

  • in arid regions stretching from North Africa to South Asia.

  • During the dry weather typical in these ecosystems,

  • desert locusts live a solitary lifestyle.

  • Adolescent hoppers will spend a few lonely weeks foraging for plants,

  • before growing wings, reproducing, and dying.

  • But when a region receives an abundance of rain,

  • the scene is set for a startling transformation.

  • Increased moisture supports more vegetation

  • for newly hatched hoppers to eat,

  • leading large groups to feed in close proximity.

  • The frequent contact stimulates their leg hairs,

  • triggering the release of a hormone

  • that causes them to actively cluster even closer.

  • Gluttonous crowds of locusts produce huge amounts of poop,

  • which carries a pheromone that furthers their transformation.

  • The hopper’s diet shifts to include plants with toxic alkaloids.

  • Soon, the locusts take on a striking pattern that warns predators

  • of their newly poisonous nature.

  • Smaller groups merge into bands of millions,

  • which mow down virtually all plant life in a kilometer-wide swath.

  • Roughly every week they shed and expand their exoskeletons,

  • growing to roughly 50 times their hatching weight in just one month.

  • Finally, the metamorphosis is complete.

  • The adults beat their translucent wings and take flight

  • as a full-fledged locust swarm.

  • In this gregarious phase, these long-winged, brightly colored creatures

  • appear so different from their solitary counterparts

  • that they were long thought to be a separate species.

  • A typical swarm contains more locusts than there are humans on the planet,

  • covering hundreds of square kilometers in a dense cloud.

  • At these numbers, desert locusts easily overwhelm their predators.

  • A large swarm can match the daily food intake of a city of millions,

  • and flying with the wind,

  • the insect invasion can travel up to 150 kilometers a day.

  • This living tornado can also cross large bodies of water.

  • In 1988, a swarm even managed to traverse the Atlantic Ocean.

  • The locusts likely formed rafts to rest at night,

  • before fueling up in the morning with a nourishing breakfast of their dead kin.

  • While flying over land, they seek out moist soil to lay eggs.

  • Swarming mothers transfer their gregarious condition to their offspring,

  • making it likely that the next generation will form another swarm.

  • This means that while an individual desert locust lives only three months,

  • a plague can last up to a decade.

  • The potential for a years-long plague isn’t unique to desert locusts,

  • but the region they inhabit makes the prospect particularly deadly.

  • Their habitat spans some of the world’s poorest countries,

  • largely populated by people who grow their own food.

  • By consuming crops and pastures,

  • these insects directly endanger 10% of humanity.

  • Fortunately, a desert locust plague doesn't last forever.

  • When a wet period ends,

  • vegetation becomes scarce and egg laying conditions decline.

  • As existing swarms die off, new hatchlings spread out in search of food,

  • creating enough distance to prevent solitary locusts from transforming.

  • Human intervention can also help.

  • Researchers use satellite imagery to identify regions at risk

  • of becoming locust hotspots and alert local governments.

  • While most countries fight back with chemical insecticides,

  • some regions have found success using fungal diseases that are lethal to locusts

  • but safe for people and the environment.

  • Unfortunately, other modern practices are exacerbating the threat.

  • Fields densely packed with a single crop are like a table set for locusts.

  • And erratic weather caused by climate change makes swarms harder to predict.

  • If we plan to discourage lonely locusts from becoming catastrophic crowds,

  • humans need to cut carbon emissions, rethink our agriculture,

  • and generally reconsider our own ravenous appetites.

The ravenous swarm stretches as far as the eye can see.

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沙漠蝗蟲(Just add water: The garden insect that can turn into a plague - Jeffrey A. Lockwood)

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    shuting1215 發佈於 2022 年 01 月 04 日
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