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 locusts—  infamous 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.