Scientists Revealed The True Cause Of The Bible’s Great Plague Of Locusts

In the Old Testament’s Book of Exodus, God is angry with the Egyptians. His ire is caused by their refusal to free the Jews from servitude and he punishes the slaveholders with ten plagues, including everything from boils to frogs and fiery hail. When the eighth plague appears the skies darken. A massive horde of locusts descends on the land, eating every growing thing in its path.

Exodus describes the confrontation between Moses, leader of the Jews and the Egyptian Pharaoh. The great prophet threatens, “If you refuse to let My people go, behold, tomorrow I will bring locusts into your territory. And they shall cover the face of the earth… and they shall eat every tree which grows up for you out of the field.”

God is as good as his word. Exodus continues, “The Lord brought an east wind on the land all that day and all that night. When it was morning, the east wind brought the locusts. And the locusts went up over all the land of Egypt and rested on all the territory of Egypt.”

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The consequences of this plague of locusts were dire indeed. According to the biblical story the insects “ate every herb of the land and all the fruit of the trees which the hail had left. So there remained nothing green on the trees or on the plants of the field throughout all the land of Egypt.” Hail, of course, had been a previous plague sent by God.

Unfortunately, periodic infestations of locusts are just as real today as they were in biblical times. What’s more, the impact of huge clouds of the insects can be just as devastating as it was thousands of years ago. But what, in scientific terms, is likely to have caused the locust plague in ancient Egypt? For people in some parts of the world, this is much more than a mere academic question.

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Scientists have searched for an explanation of why these insects burst out into huge swarms in certain years. In recent times, researchers are beginning to form a clearer picture of what triggers these potentially catastrophic events in various parts of the world. But just how dangerous are these insect influxes today?

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Let’s start with the creature itself. We can’t know for sure the precise species of locust that the Lord unleashed on Egypt, but it may well have been the desert locust, Schistocerca gregaria. This looks very much like a grasshopper, with the characteristic oversized hind legs that allow it to leap prodigious distances. In fact, it is a kind of grasshopper.

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But what distinguishes locusts from grasshoppers most starkly is their respective behaviors. Locusts swarm; grasshoppers don’t. What’s more, when the former congregate they can travel for many miles. The beginning for locusts are eggs. Female locusts lay their eggs in sandy earth in a case with up to 150 or more individual ova.

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Each female locust can produce offspring a minimum of three times during her lifespan, with just six to 11 days between layings. Researchers have found as many as 1,000 egg pods in just a bit more than 10 square feet. The locust eggs take between ten and 65 days to hatch. At that point, life for the insect can take one of two paths.

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The young locust, called a nymph or a hopper, stays in this immature stage for between 24 and 95 days. And it can become gregarious or solitary. It’s when it becomes gregarious that huge numbers of them form swarms and farmers have something to worry about. From about two-and-a-half through to five months, the locusts reach adulthood. At this stage, the earlier process of becoming solitary or gregarious is repeated.

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It’s at the point the critters reach adulthood that they can fly. Once they’ve taken to the wing is when the voracious swarms can become really dangerous. In an article describing the life cycle of the locust, National Geographic magazine gave some truly startling facts about the potential scale of a plague of these insects.

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A swarm of locusts can cast a shadow over as much as 460 square miles. To put that into perspective, the whole of New York City’s Manhattan Island covers an area of just 23 square miles. The locust horde can include as many as 70 billion individuals. And they’re all hungry, collectively capable of chomping their way through 300 million pounds of vegetation each day.

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Locust hordes tend to be described as a plague when multiple swarms fly together. Naturally, it would be advantageous if scientists could predict exactly when such events will occur. But researchers have found no discernible pattern in the years when the insects congregate on so massive a scale. For example, the mid-20th century saw swarming in the years from 1926 to 1934, 1940 to 1948 and 1967 to 1969, among others.

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The other characteristic of swarming locusts which makes them such a devastating pest is their ability to travel over long distances. They have been known to travel more than 80 miles in one day, and locusts can stay in the air long enough to span large areas of water. They’ve been recorded flying right across the Red Sea which divides Egypt, Sudan and Eritrea from Israel, Saudi Arabia and Yemen.

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We can go right back to 1954 for one extraordinary locust event. In that year, according to National Geographic, a swarm flew all the way from the north-west of Africa, landing in Britain. And 34 years later another locust horde made it from west Africa to the Caribbean in a journey lasting just ten days. That’s a distance of some 3,100 miles.

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Nowadays, plagues of locusts occur in a variety of countries. But it’s in African nations that the effects of the voracious critters are felt the most. There, the bugs can have a catastrophic effect on subsistence farmers, who depend on the crops they grow for their food. A year when the insects are at their most active can mean food shortages and even starvation.

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About one-fifth of our planet’s land area is susceptible to the consumptive habits of desert locusts. That’s something like 60 different nations that may fall victim to their swarms. However, when there are years that the insects are less active, their habitat shrinks to include roughly 30 countries, still an area of 6 million square miles.

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In the years that they swarm, locusts can be a threat to as much as 10 percent of the world’s population. Before the swarms that hit various countries in 2020, of which more in a moment, the last major outbreak of gregarious desert locusts came between 1986 and 1989. Nations in Africa and the Middle East suffered during that period of swarming.

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But it’s not so long ago that the U.S. experienced periodic swarms of grasshoppers. When they swarm, their impact pretty much mirrors that of locusts. There was a particularly bad episode in 1937 in Colorado. The insects appeared in huge numbers in the south-eastern part of the state, with the potential to spread to neighboring New Mexico and Kansas.

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At the height of the Great Depression, and with a continuing drought to boot, this added calamity was the last thing that farmers in Colorado needed. In fact, scientists had spotted that there might be a problem on the horizon during the previous fall. They’d come across nests in their millions, each with multiple eggs.

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The eggs hatched out in June 1937. At first, the insects were in the hopper stage, unable to fly, but soon their wings developed and they were able to travel across the Colorado landscape. Later, Popular Science magazine was to report that even the flightless insects wreaked devastation. Their seemingly tireless appetites saw them rip through agricultural land in the state.

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What’s more, it seems that green vegetation was not the only thing that caught the attention of these insatiable critters. The Popular Science reporter wrote, “Unable as yet to fly, the hungry hoppers chewed at fence posts, clothing, hair on cattle – practically anything they could find that would fill their hungry stomachs.”

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The Governor of Colorado Teller Ammons was alarmed enough that he declared a state of emergency and summoned help from the National Guard. And, according to a 2014 article on the National Guard website, he gave short shrift to those who accused him of overreacting. It was a full-scale emergency as far as he was concerned.

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Ammons declared, “Some people are making jokes out of the fact that the National Guard was called into service to help fight the grasshopper plague. But it is one of the most serious situations that ever confronted Colorado and I only wish I had more trucks and equipment that could be thrown into this war on those insects.”

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And the National Guard took no half measures. They actually fired flamethrowers at the insects from trains moving at walking pace. Sadly this intervention, dramatic though it was, proved to be ineffective against the swarm. However, it did allow trains to run along rails otherwise rendered too slippery by the thousands of crushed locusts.

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Undeterred by the failure of the flamethrowers, the National Guard now turned to an even more drastic tactic. Brigadier General Alphonse J. Ardourel described the outcome of this method to newspaper The Denver Post. He admitted, “We tried dynamiting. They kept right on flying – just bounced a little and went on. These hoppers are terrible.”

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At one point the U.S. Bureau of Entomology’s senior scientist, Dr. J.R. Parker, threw his hat on the ground – presumably in despair – while visiting Colorado Springs. When he lifted his headgear from the ground he decided to count how many he’d trapped: the total came to 247. One expert estimated the locust numbers at 7 billion in 10 square miles.

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Eventually, the good folk of Colorado hit upon a solution. What they needed to do was to turn the insects’ ravenous appetites against them. Poison was the answer. Once they’d hit upon that insight, the experts set to work with a will. A bran and molasses mixture, a toothsome snack for the hoppers, was made into a lethal meal by combining it with sodium arsenite.

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Guardsmen, farmers and even planes from the Colorado Army Air Corps were enlisted to help spread the poison around the affected areas. This stratagem did the trick. The downside was the terrible smell generated by millions of dead grasshoppers. An unexpected upside was the extra income from selling the little corpses as bait to fishermen.

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While, as previously mentioned, the story of that grasshopper plague in Colorado dates back to 1937, in 2020 terrible hordes of locusts were reported to be ravaging parts of Africa. British news broadcaster the BBC headlined a website report in August with the apocalyptic, “The Biblical locust plagues of 2020.” Countries in East Africa and the Middle East, from Kenya to Saudi Arabia, were indeed suffering the worst insect swarms for many years.

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We’ve seen the methods used to combat these fearsome insects in the U.S. back in the 1930s. But what do people do now to try and rid themselves of this pestilence? African farmers, without access to advanced methods, have had to resort to beating drums, burning tires and even just shouting in an effort to deter the insects. As you can imagine, these methods are far from effective.

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Much more potent is the aerial and land-based spraying of pesticides, a tactic adopted by the Kenyan government. And it’s an urgent task. According to the BBC, further swarms could result in as many as 25 million people suffering severe food shortages. As many again could find themselves unsure of the reliability of consistent alimentary supplies.

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Various other methods of defeating the swarms are being trialed. Electrified metal grids can be dragged through fields; this disturbs the insects and encourages them to fly off. Then there are biological solutions: a fungus, Metarhizium acridum infects locusts and kills them. But this could also have the side-effect of killing beneficial insects.

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In the case of the ancient Egyptian plague described in Exodus, The Daily Telegraph newspaper reported an interesting theory in 2010 from Siro Trevisanato, a Canadian biologist. He theorized that swarms may have been triggered by the massive volcanic eruption that occurred on the Greek island of Santorini. This Santorini eruption in 1646 B.C. was indeed cataclysmic, probably one of the largest since modern humans walked the Earth.

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The Santorini volcano exploded with an estimated force equivalent to 40 nuclear bombs and it vaporized the center of the island. Trevisanato told the newspaper that, “The ash fallout caused weather anomalies, which translates into higher precipitations, higher humidity. And that’s exactly what fosters the presence of the locusts.”

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Perhaps the greatest boon will come from a better understanding of what makes locusts swarm. And on this front, there is real hope. As we’ve seen, desert locusts live solitary lives for years. But then they flock together, start swarming and go on to cause widespread devastation. What triggers this drastic change in their behavior?

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That is the very question which researchers from Cambridge and Oxford universities in England and Australia’s Sydney University addressed. The initial impetus for these locust congregations is environmental, something that’s long been recognized. But the researchers made a surprising discovery about what happens to the physiology of locusts when they gather together.

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In times of drought, the desert locusts are forced into closer proximity by the shortage of food. And once they’re in a crowd, their chemical make-up is transformed in a matter of hours. They begin to produce the neurochemical serotonin. That’s present in many creatures, including humans. In us, the chemical has various important roles including the moderation of mood.

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Researchers believe that this flood of serotonin into the central nervous system causes the locusts to become gregarious and start gathering in large numbers. That knowledge raises the potential prospect of an effective solution. If scientists could find a way to curtail the insects’ serotonin production, this in turn could stop their swarming behavior.

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Speaking to The Independent newspaper in 2009 about the discovery of the role of serotonin in locust behavior, Steve Rogers of Cambridge University said, “The gregarious phase is a strategy born of desperation and driven by hunger: swarming is a response to find pastures new. We have now found the mechanism that controls the process. We’ve opened the black box of how this works.” Will this lead to an end to the insect plagues which have dogged humanity since at least the time of Moses? Let’s hope so.

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