Locust are one of the world's most devastating pests. A kind of metamorphosed grasshopper, they can eat their own weight everyday and can invade all or parts of 65 countries from West Africa to India to Australia, affecting 20 percent of the of the earth’s land. In 2008, a locust swarm nearly seven kilometers long plagued Australia. [Sources: Robert A.M. Conley, National Geographic, August 1969; Jane Brody, New York Times, May 17, 1988]

Locust swarms with 40 billion insects have reached an altitude of 10,000 feet. One locust expert told the New York Times, "No other insect in the world travels so far, over such inhospitable country, merely to keep alive, and none is swiftly able to expand both in its numbers and its territory when conditions develop in its favor."

Locusts of have been around much longer than man has. They were mentioned in the Bible and painted in the tombs of Egyptian pharaohs. In the Old Testament, they were the eighth of the ten plagues of Egypt released by Moses. Exodus 10:3 reads: "For 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 no any green thing, neither tree nor plant of the field, through all of the land of Egypt." In Revelation in New Testament swarms of human-faced locusts emerge through smoke from a bottomless pit during the Rapture that marks the end of the world.

Locusts eat pretty much anything: grains, fruits, vegetables, leaves. When people throw blankets over their crops to protect them, the locusts simply eat the blankets. Unfortunately for people that live in locust-plagued regions the same consistent rains that bring bountiful harvests also produce ideal conditions for locusts. Damage by locusts can result in crop damages and famine that can last for years.

Locusts are a kind of grasshopper. Grasshoppers have wings but don’t fly very well. The first segment, or femur, of the hind leg is long and wide, containing powerful muscles that can launch the insect to their spectacular jumps, with their wings used to extend their flights. On the second segment, or tibia, of the hind leg are a line of nasty barb that help defends the insects from attack from behind. Birds such as crows that regularly feed on grasshoppers have dense tufts of hair that thick out from the bases of their beaks that help protect their eyes.

Websites and Resources on Deserts: United States Geological Survey ; Desert USA (good info on the world’s deserts); ; United Nations Global Desert Outlook ; Desert Biome article, University of California, Berkeley Desert Biome ; Blue Planet Biomes (about U.S. deserts) ; Wikipedia article Wikipedia ;National Geographic online article National Geographic Oxfam Cool Planet ; Sand Dunes article ; United States Geological Survey

Locust Life Cycle and Metamorphosis

Until 1921, when Sir Boris Uvarrov discovered the grasshopper-to-locust metamorphosis nobody knew where the massive locust swarms came from.

Most of the time the desert locust, known scientifically as Schistocerca gregaria, is solitary grasshopper that moves by night and eats scrubby desert plants during the day. Only when conditions are right do these grasshoppers seek the company of others and go through the profound metamorphosis into locusts.

Solitary grasshopper females live about ten months. They lay two or three batches of 80 eggs before they die. The flightless "hoppers" that emerge from the eggs are nymphs or instars. They shed their rigid skeleton skin five times as they grow into adults.

The metamorphosis from grasshoppers into locusts occurs after repeated rains cause the eggs of thousands of grasshoppers to hatch. The grasshoppers themselves go through an amazing transformation. They begin seeking the company of others and turn from brown to yellow, black and red. In addition, their hind legs shorten, their wings lengthen and their faces become meaner-looking. When the rains stop and vegetation because sparse the locust turn back into grasshoppers.

Scientists are still not sure what sets in motion the metamorphosis. Although rain is clearly a determining factor, the metamorphosis often begins before the rain falls. Some scientists think the change is activated by touch. Others think it may be triggered by hormones. Some studies suggest that desert shrubs that bloom in anticipation of rain maybe is involved somehow.

Locust Mating Behavior After the Metamorphosis

After the metamorphosis, locusts begin copulating and laying eggs when it rains. The females lays eggs, which need moisture, in the sand. Moist sand is ideal and the female can hold her eggs for 52 hours before laying them using a needlelike abdomen, which can stretches to twice its length. The young emerge in a white foamy substance that prevents them from drying out.

Adults live a shorter life as locusts than they do as grasshoppers. They breed soon after becoming adults, with the females laying about 80 eggs once, and then die. If the weather conditions are right the eggs hatch in 10 to 14 days. If the weather is too dry or too cool, the eggs can remain dormant for up to two or three months.

Under swarming conditions, hoppers gather in large groups and march across the desert, eating and shedding their skin. They can travel up to a mile a day, eating all the way, and covering as much as 10 to 15 miles during the five or six week hopper stage.

Locust Swarming and Feeding Behavior After the Metamorphosis

Locust normally live for four months and reach a length of three inches. They can eat the equivalent of their own weight in every day or go for four day without eating, living off of stored body fat. If there is no food they eat one other or slow their body processes until conditions improve, and this way may live as long as year.

Although birds, beetles, flies and wasps feed on locust they are not enough of them make much of a dent on a large swarm. Hopper groups can enlarge their size to intimidate avian predators.

When the temperatures become extremely cold, the locusts can form themselves into a ball that continually changes position so some locusts can get warm while others shield them from the cold. A similar process takes place when temperatures are warm.

When the rains die out the locust take wing and form swarms to search for food and favorable living conditions.

Locust Swarms

When the grasshoppers are in their solitary stage, there may be only a few thousand of them over an area of many of square miles. But when the swarms form there may be as many as 150 million in one square mile. In their densest concentrations it is difficult to take a step without hearing the crunch, crunch, crunch of locust bodies being crushed bodies under foot in addition to the sound of “millions of jaws biting and chewing.”

A typical locust swarm contains over 5 billion locusts and covers 60 square miles. Large swarms can cover an area the size of greater London. One of the largest locust swarms ever recorded — in Ethiopia and Somalia in 1958 — covered 400 square miles and contained an estimated 40 billion locusts, capable of eating 80,000 tons of food a day. The swarm destroyed 167,000 tons of crop in Ethiopia alone and thousands or people starved to death.

Describing a swarm of locusts at friend's small farm in the Sudan, journalist Robert Conley wrote: "A hint of grayness slid along the sand, vague as a touch of smoke. gathered into a wisp and began to spill over the dunes...until it became a cloud of locusts three miles wide that swept straight towards us...[then]...swirled into us. Flying locusts the size of index fingers bounced off my face, tangled in my hair and grabbed at my shirt with twitchy legs...I yelled...but my voice was lost in the rush of wings. We fought for an hour to save his crop...we slashed at the intruders with the reeds...and banged sticks against them. We ran up and down the rows throwing stones; and in the end, in the 110̊ heat, we knew we had lost."

"All around us," he wrote, "locusts struggled for room on the plants; they pushed, kicked and shoved each other, semaphoring furiously with excited antennae. They ravaged the ears on top. They tugged at the leaves. They gnawed at the stems with such frenzy that we could hear the faint sound of thousands of tiny jaws grinding and chewing, as if someone were scraping a carrot. 'Come, my friend,’ Khalil finally said...'these locusts, they laughed at us.’"

Formation and Movements of Locust Swarms

Certain conditions favor the creation of locust swarms: unusually heavy desert rains, favorable winds, good crops after periods of drought, a ban on long lasting pesticides and civil strife that disrupts control efforts. Rains foster egg development and promote quick growth of plants the locusts feed on.

When otherwise harmless juvenile locusts get too crowded, they will suddenly align themselves and march in the same direction, triggering a potentially devastating swarm.

Locust swarms have no particular course of action and no idea of where they want to go. They are transported primarily by the winds and whether the end up in a field or barren patch of desert or even the sea is primarily a matter of luck. Ideally they hope to ride a wind to a place where winds converge and produce rain.

Locust can stay aloft for 17 hours at a time, and if the winds are strong enough they can range 3,000 miles in their lifetime.

Swarms can remain active over a long period in a large area. In 1985 and 1986, locusts began breeding around the Red Sea. They moved into Sudan in the summer of 1986. Civil war there hampered control efforts and they invaded North Africa and Arabia in the summer of 1987. Good rains in those areas allowed more breeding than usual.

Swarm Theory and Locust Swarms

Swarm theory is being studied to gain deeper insight into how locust swarms behave and find ways to prevent them from occurring.

Iain Couzin, an expert on swarm theory at Oxford University, traveled to remote areas of Mauritania to study the behavior of locust swarms. He has also studied locust in a laboratory using a circular track. His team found that when density levels rose above a certain threshold the insects suddenly began to move together with each locust trying to align its movements with those of its neighbor.

Couzin has said that understanding how animals swarm and why they swarm are two very different questions. He told the New York Times that swarms of locusts may look similar to swarms of Mormon crickets in the United States but the reasons behind them are quite different. While the locust are aligning their movements and behavior the crickets are trying to cannibalize some neighbors and avoiding being eaten by others. The cricket swarms — which can number in the millions and reach eight kilometers across — are prompted by shortages of protein and salt. “Each cricket itself is a perfectly balanced source of nutrition,” Couzins said, “So the crickets, every 17 seconds or so, try to attack other individuals. If you don’t move, you’re likely to be eaten...All these cricket are on a forced march. They’re trying to attack the crickets who are ahead, and they’re trying to avoid being eaten from behind.”

Serotonin and Locust Swarms

Studies by Malcolm Burrows of Cambridge University suggest that serotonin — the chemical that affects the moods of humans, reportedly making them happier — plays a role in locust swarming behavior. In an article published in Science in February 2009, Burrows reported that when packed close together the amount of serotonin in their systems triples and they begin going into swarm mode. “Here we have a solitary and lonely creatures, the desert locust,” Burrows told AP, “But give them a little serotonin and they go and join a gang.”

Members of Burrows team tested locusts for a number of chemicals and found that serotonin was the only one that had an impact on their behavior. To test there theory further they injected solitary locusts with serotonin and sure enough they changed into swarming creatures in a couple of hours. The scientists also found that the production of serotonin could be induced naturally by tickling the back legs of the locusts for several hours.

Locusts produce more serotonin when circumstances force them together such as a drought or food shortage. The sight, smell and touch of other locusts stimulatea the production of the chemical. When swarming locust were given drugs that blocked serotonin, swarming behavior was thwarted.

Locusts as Food

People who are victims of locust attacks often also eat locusts. When swarms swoop down people scoop them up off the ground or collect them in nests or baskets and cook them in boiling water. They are an excellent source of protein. The Jewish Talmud recommends eating them from time to time. The Bible classifies locusts and grasshoppers as “Clean.” After locusts raid crops often there is nothing else to eat and thus people have traditionally eaten them during locust-exacerbated famines.

According to the Oxford Companion to Food by Alan Davidson, locusts can taste like the "the yellow of a boiled egg" or "not unlike whitebait that, somehow, have been stuffed with buttered toast." Locusts fried in oil are said to taste like shrimp.

In poor countries locusts can be made into toys. Children sometimes make belts of dead locusts and attach strings to live ones and let them fly around like toy airplanes.

Locust Control

Efforts to control locusts include poisoning their breeding grounds, burning them, burying them and poisoning them directly. People have also tried lighting fires to scare them off, blasting off shotguns, and spreading molasses to entrap them in sticky goo. Trenches have been dug to halt the march of hoppers. During World War II, the British sprayed highly toxic arsenic to kill them.

In Ethiopia religious hermits are sometimes called in to protect villages from swarms. After fasting for several days, sipping only a mixture of milk, honey and an herd that locust find unpalatable, the hermit catches seven locusts in the folds of his cloak. He then gives three of them names and releases them with a kiss while reading a prayer from a special book. The hope is that the locust swarm will follow the cast-off locusts away from the village. One line from a locust-banishing prayer goes: "Locusts! May your mouths be as hard and dry as iron.”

Locusts are most vulnerable when they are in the hopper stage. To minimize environmental damages pesticides that are only active for a short time are used. As a result an infested area has to be continuously sprayed as new hoppers emerge.

Eradication programs sponsored by the United Nations and agencies like the Desert Locust Control Organization for Eastern Africa spray swarms in the air with an oily pesticide that penetrates the locust's skin and doesn't evaporate in addition to ground spraying areas occupied by flightless hoppers with a mist-producing atomizer that hooks up to the engine of a Land Rover. Monitoring stations and satellite imagery are used to keep track of the swarms which often end up in zones of converging winds.

Relatively New Methods of Locust Control

In the late 1980s, Russian and American scientists came up with a novel way of attacking locusts. First the swarms are spotted with U-2 spy aircraft by following their trail of defoliation and then fried with a ten foot wide laser beam. [National Geographic Earth Almanac, October 1990].

Pesticides used to combat locust can be harmful to the environment. Scientists have had some success using an environmentally-friendly fungus that can be sprayed and kills the locust in 5 to 10 days. A mixture of fungus spores mixed with oil, marketed under the name Green Muscle, shows great promise in controlling locusts. Used to kill millions of locusts and grasshoppers in Niger, it is a naturally occurring substance that kills locust but is harmless to other life forms and is so safe that people can eat it. It costs about the same as pesticides and is much less harmful to the environment.

The discovery of the link between swarming and serotonin described above offers hope for tackling locusts. Stephen Rogers of Cambridge University told AP, “It opened up a whole line of inquiry into what we could do to break apart these swarms before they develop.” But he added, “You need to get it at an early stage. Once you have several million or billion locusts there is a limit to what you can do.”

Problems with Locust Control

Once locusts begin breeding and swarms form there are simply too many locust s to control with spraying.

Another problem is finding the places where locusts breed and getting the necessary locust-fighting resources there. David Nickle, an entomologist with the Smithsonian told the New York Times, "There's a lot of Africa where they can develop and not be seen by people. Then, once found, there’s the problem of getting control chemicals to remote areas, which usually requires an airplane, and that's very expensive."

Civil wars, weak governments and failed state conditions like those in Somalia hamper surveillance and spraying.

Image Sources:

Text Sources: "Deserts Geology and Resources" by A.S. Walkers, USGS Online publication; Rick Gore, National Geographic, November 1979 [┵]; New York Times, Washington Post, Los Angeles Times, Daily Yomiuri, Times of London, National Geographic, The New Yorker, Time, Newsweek, Reuters, AP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.

Last updated March 2011

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