Summary: Locust swarms occur when populations of locust become dense. The crowding forces them to touch and this constant touching triggers a change in their usual solitary behavior.
Locusts are related to grasshoppers and they look very much the same. Their behavior, though, is different. Grasshoppers are solitary creatures. Locusts are solitary most of the time, but when conditions are right they will join together into terrifying and highly destructive swarms.
A locust swarm can cover an area that is over 450 square miles and can contain billions of locusts, densely packed together. They fill up the sky reminding you of Alfred Hitchcock's horror movie "The Birds." Everywhere you look the sky is crowded with dark flying creatures criss-crossing paths.
A locust swarm is terribly destructive. Each locust can eat its body weight every day and a large swarm can eat as much as 423 million pounds of plants a day. The locusts eat everything in their path. When they have destroyed the vegetation in one area they move on to the next. The results can be tragic. Famines often follow locust swarms causing starvation for humans and animals alike.
Locust swarms have been recorded throughout history. The horrors of a locust swarm are vividly described in Exodus in the Bible, where locusts were the eighth plague in Egypt: "They covered the face of the whole earth, so that the land was darkened; and they did eat every herb of the land, and all the fruit of the trees which the hail had left: and there remained not any green thing in the trees, or in the herbs of the field, through all the land of Egypt."
Today, locusts are found in 60 countries, but the swarms do the most damage in Africa, especially in areas of sustenance farming.
Scientists have recently discovered that the nervous-system chemical serotonin plays an important role in creating locust swarms. That's the same chemical that we humans have in our brains, the chemical that anti-depressants like Prozac are supposed to increase. In locusts, the serotonin triggers their swarming behavior. Locusts usually stay by themselves, but when some condition like a drought forces them to crowd together, they smell and see and touch each other. Scientists found that the smelling, seeing and touching are triggers that increase the amount of serotonin that the locusts produce. The serotonin, in turn, changes them from solitary to gregarious creatures and that's how swarms begin.
This is an exciting discovery because it points the way to possible future methods of preventing the damage caused by locust swarms. Right now, the only way to combat swarms is by using chemical pesticides which are not always effective and which may be harmful to the environment. Now that we know that increased serotonin levels cause locusts to swarm, scientists are working on finding a way to block serotonin production in locusts to prevent the swarms from starting.
It's hard to find many good things to say about locusts, although some people do like to eat them. Some cultures consider locusts delicacies as they are rich in protein. They may be boiled, roasted, barbecued, grilled or pan-fried. Also, some people like to keep locusts as pets. Mostly, though, locusts have been a plague on humanity. We are lucky to be living in a time when scientists may soon find the key to making locusts swarms a thing of the past.