When Grasshoppers Go Biblical: Serotonin Causes Locusts to Swarm

When Grasshoppers Go Biblical: Serotonin Causes Locusts to Swarm

A common brain chemical could be behind the process that morphs timid grasshoppers into voracious locusts

  • By Katherine Harmon on January 30, 2009

“data-newsletterpromo-image=”https://static.scientificamerican.com/sciam/cache/file/458BF87F-514B-44EE-B87F5D531772CF83_source.png”data-newsletterpromo-button-text=”Sign Up”data-newsletterpromo-button-link=”https://www.scientificamerican.com/page/newsletter-sign-up/?origincode=2018_sciam_ArticlePromo_NewsletterSignUp”name=”articleBody” itemprop=”articleBody”>

What makes harmless little green grasshoppers turn into brown, crop-chomping clouds of swarming locusts? Serotonin, according to a study published this week in Science. Researchers from universities in the UK and Australia found that that neurotransmitter (a chemical compound that sends impulses between nerve cells and affects everything from sleep to aggression in humans) spurs a cascade of Dr. Jekyll-to-Mr. Hyde–like changes in at least one species of grasshopper — the desert locust (Schistocerca gregaria). This species is infamous for wreaking havoc from Africa to Asia.

Knowing what causes this swift metamorphosis may help governments and farmers develop methods to control future locust outbreaks with chemicals that would suppress the offending serotonin.

It took just two to three hours for timid grasshoppers in a lab to morph into gregarious locusts after they were injected with serotonin. Conversely, if they were given serotonin blockers, they stayed solitary even in swarm-inducing conditions.

“These little guys changed from a shy creature that actively avoided making contact with other grasshoppers [into a creature] actively seeking out other insects and joining a gang,” says study co-author Malcolm Burrows, a zoology professor at Cambridge University in England. And we’re not just talking about a gaggle of grasshoppers: Just last year, a swath of locusts more than three and a half miles (six kilometers) long tore through Australia, devastating crops in its path.

“They eat everything in sight,” says Sean Mullen, an assistant professor of evolutionary genetics at Lehigh University in Bethlehem, Pa., about swarming locusts.

When these insects go into swarm mode, they don’t just get super social, they also completely change physically, becoming stronger, darker and much more mobile, says study co-author Swidbert Ott, a research fellow at Cambridge. In fact, he says, the before-and-after bugs look so different that, until the 1920s, they were assumed to be two unique species.

In the wild, swarms usually appear after a rainy period followed by a time of drought. After rains, populations of grasshoppers explode, Burrows says, because there is food aplenty. But when the land becomes parched and grass scarce, the populations get pushed into smaller and smaller areas, becoming more packed as desirable pasture diminishes, he says. At a certain point of density, the swarm-inducing serotonin gets triggered and the locusts set off en masse to find greener pastures. After that, few things — other than an end to the food supply or an ocean — can stop them.

Burrows says that locusts can switch out of swarm mode, though it takes days rather than hours. He notes, however, that the about-face rarely happens in the wild, because the offspring of locusts that breed while swarming are born swarmers.

Today, locust invasions are controlled with pesticides that also wipe out other insects, note Burrows and Ott. This new research, however, paves the way for development of a chemical that would specifically inhibit serotonin production in the solitary grasshoppers, says Hojun Song, a postdoctoral researcher at Brigham Young University in Provo, Utah.

But remember, as Kung Fu‘s Master Po advised his young charge in the 1986 movie, “Do not go in fear, Grasshopper.” Of the approximately 8,000 species of grasshoppers, only about 10 of them are likely to morph into swarming locusts, Burrows says. But, Song adds, more research should be conducted to determine whether other types of locusts also get hopped-up on serotonin.


What Is the Difference Between Grasshoppers and Locusts?

Grasshoppers vs. Locusts—they both look they same, so it makes sense that telling them apart can be a little confusing. Despite some obvious similarities in appearance, there are some distinctions when it comes to these insects. What is the difference between grasshoppers and locusts? Let’s clear a few things up.

What Is a Grasshopper?

Grasshoppers are insects that eat plants. They are medium to large in size (anywhere from 1 to 7 centimeters in length), with the females being larger than the males. These insects can leap up to 20 times the length of their bodies. There are approximately 11,000 different grasshopper species worldwide. They are found everywhere in the world, with the exception of the extreme polar regions, because it is too cold.

Grasshopper Characteristics

Grasshoppers are closely related to katydids and crickets. Like these other insects, grasshoppers have two sets of wings—one narrow and resilient, while the other is wide and pliable—long hind legs for jumping, and mouthparts made to chew. Unlike katydids and crickets, the antennae on some grasshoppers are short. The length of their antennae classifies them as either long-horned grasshoppers or short-horned grasshoppers.

When it comes to the coloring of grasshoppers, they are colored in ways that allow them to blend in with their environment. They are often green, brown, or gray, although in some species, the males have bright colors on their wings to attract females. If a grasshopper is brightly colored, they often eat toxic plants. They store the toxins in their bodies, and their color warns predators that they are dangerous.

Grasshopper Diet and Habitat

Grasshoppers are commonly found in fields or meadows. However, they can thrive anywhere that has enough food. They are voracious eaters and, on average, eat 16 times their body weight. Their favorite foods include cereal crops (crops such as barley, wheat, rye, rice, and oats, among others ), leaves, and grasses.

Grasshopper Predators

The greatest threat to grasshoppers are flies. Often, they lay their eggs near the grasshopper’s eggs, and when the flies hatch, they eat the grasshopper eggs. Some flies lay eggs on the grasshopper’s body, and the larvae then consume the grasshopper. Other predators include spiders, beetles, snakes, birds, and mice.

What Is a Locust?

A locust is a grasshopper that develops gregarious characteristics. The environmental conditions have to be suitable to allow the grasshoppers to form into an organized group. These conditions can include dense vegetation growth after a drought. For example, during a drought, locusts are driven to small areas of vegetation. They abandon their solitary phase, which is common for grasshoppers, and reproduce at incredibly high rates. Transitioning from the solitary phase is signaled when the grasshoppers secrete serotonin. Locusts move together as a group, making stops on any patch of green that they notice and causing extensive and devastating damage to crops, covering long distances in a short period of time.

What Is the Difference Between Grasshoppers and Locusts?

Both grasshoppers and locusts are similar in appearance, and they also have similar morphological structures. However, when grasshoppers change into locusts, their wing structures change. As locusts, they need to be able to fly longer distances, so their wings become longer and stronger. A locust also has a smaller body than a grasshopper.

Locusts also have the ability to exist in the solitary or gregarious phase, while grasshoppers can only be solitary (although, they get together to mate). Locusts come into being when the need for food becomes desperate, and they’ll do what they can to ensure their survival.

Humans, Grasshoppers, and Locusts

Humans have been known to use both grasshoppers and locusts as a food source . Both insects are responsible for the mass devastation of crops, a trait that doesn’t exactly endear them to the farming community. To combat this issue, pesticides and biological control methods have been developed by science to keep grasshoppers and locusts under control.

In essence, a locust is a grasshopper that has developed social characteristics. More often than not, the short-horned grasshopper will morph into a locust, but there have been cases where other grasshopper species have become locusts. The only thing a grasshopper really needs is for the environmental conditions to be right, and they’ll turn into a locust. Now you know!


Grasshoppers vs. Locusts: What Makes a Swarm?

Grasshoppers are in the news again. Or are they locusts?

Last week we learned locusts were swarming in Ethiopia, wiping out crops vital to the survival of local people.

Now we hear grasshoppers are invading Tooele County, Utah, near Salt Lake City. They’re all over the ground, with people crunching them underfoot. The infestation is “worse than anyone can remember,” AP reports.

What’s the difference between the two bugs?

Green grasshoppers and brown locusts are close cousins, both in the grasshopper family. But while grasshoppers hop like mad and can be abundant and pesky, locusts can fly. More significant, locusts have the unusual ability to be total loners or to enter what scientists euphemistically call “a gregarious state” — this is the flying and swarming stage, the stuff of Biblical proportions.

Desert locusts affect 20 percent of the world’s land surface, scientists say. Vast swarms containing billions of bugs periodically devastated parts of the United States back when the West was being settled. They continue to be a big problem in parts of Africa and China. Last November, swarms nearly 4 miles long (6 km) plagued Australia.

What makes them so, um, gregarious?

An increase in the chemical serotonin (which boosts moods in humans) in certain parts of a locust’s nervous system initiates the swarming behavior, according to a study published earlier this year in the journal Science.

It’s nature’s way of giving wing to a starved creature.

Desert locusts live in barren regions that see rain only rarely. They eke out an existence alone when times are tough. When the rains come, they breed like crazy. Then things dry up, and hoards of locusts are forced to gather around dwindling patches of vegetation.

“The gregarious phase is a strategy born of desperation and driven by hunger, and swarming is a response to find pastures new,” said study team member Steve Rogers of Cambridge University.

Rogers and his colleagues found that in the lab, solitary locusts could be made gregarious within 2 hours simply by tickling their hind legs to simulate the jostling they experience in the wild. Serotonin levels spiked three-fold.

Once on the move, the epic swarms are all but inevitable. Here’s how that works:

Scientists discovered a few years back that at low densities, the insects were unorganized and went their separate ways. But when the group’s density increased, the bugs fell into an orderly line and began to follow the same direction.

Such “collective motion,” which spells doom for a crop, is common also among ants, birds and fish.

The grasshoppers now invading Utah are born in cycles that run 7 to 10 years, scientists say, and the outbreak is nothing unusual for the natural world. What’s really new is that there are more suburbanites to complain about them now.

In The Water Cooler, Imaginova’s Editorial Director Robert Roy Britt looks at what people are talking about in the world of science and beyond. Find more in the archives and on Twitter.


What is the Difference Between Grasshoppers and Locusts?

Green grasshoppers and brown locusts are close relatives of one another.

Grasshoppers and locusts are closely related insects both in the Acrididae family. Locusts are in fact, grasshoppers which develop gregarious behaviors under optimum environmental conditions which involve the presence of large populations of grasshoppers. Locusts are not themselves a species. The two insects are primarily herbivores feeding on any green matter they come across and are sometimes agricultural pests when they land in farms. Grasshoppers and locusts have had interactions with human beings since early times and have been mentioned both in the Quran and in the Bible. The two are often used as a delicacy across many communities of the world providing a source of protein.

What Are Grasshoppers?

Grasshoppers are ground dwelling insects which go through a phase of incomplete metamorphosis before developing into the adult stage. As grasshoppers mostly occupy the ground, they have very powerful hind legs which are adapted for escape in case they are threatened. Grasshoppers are closely similar to locusts though grasshoppers can only fly for shorter distances. Grasshoppers mostly exist within a solitary phase with little to no threat to crops. Within the solitary phase, grasshoppers are disorganized, each leading its way of life. However, some grasshopper species develop gregarious behavior under suitable conditions becoming more like locusts.

What Are Locusts?

Locusts are grasshoppers which develop gregarious characteristics in suitable environmental conditions forming an organized group. Such conditions are particularly driven by a period of dense vegetative growth after drought. Drought drives locusts to crowd in small areas where there is vegetation. Locusts then abandon their solitary phase as grasshoppers and reproduce at dramatically high rates forming bands of nymphs and swarms as adults. The transition from the solitary phase is triggered by the secretion of hormone serotonin which has been linked to boosting moods in humans. In their swarms, locusts move in a single direction making stopovers on any green area they notice. This movement causes extensive damage to crops. Locusts are known to cover long distances in short time periods leaving behind a trail of damage.

A swarm of locusts.

Structural Differences Between Locusts And Grasshoppers

Though similar in appearance, grasshoppers differ structurally from the locust. Both species have similar morphological structures whose major difference occurs when locust become gregarious. In grasshoppers, the front wings are thin and tough while the outer wings are wide and flexible. In locusts, the wings become longer and stronger to allow for long distance flights. The body of locusts are smaller than that of grasshoppers. In their solitary states, female locusts are larger than their male counterparts, although their sizes do decrease in the swarming phase.

Behavioral Differences Between Locusts And Grasshoppers

Grasshoppers are primarily solitary creatures throughout their lives, coming together only for reproduction. Though locusts may be found in isolation, they mostly occur in groups in which they forage, bask and roost. Grasshoppers are relatively sedentary species maintaining the same habitat for long periods of time. Grasshoppers only move when threatened and during feeding. Locusts, however, are migratory species often shifting from one area to the next in search of food. Even in their solitary states, locusts are still known to fly over long distances.

Human Interactions With Locusts And Grasshoppers

Grasshoppers and locusts are popular species among humans especially as a source of food. However, they are infamous for mass destruction of crops – a problem that has plagued farmers for centuries. Swarms of locusts are often a bad omen for farmers and have resulted in several droughts in areas where they land. As a countermeasure, scientists have developed the use of pesticides as well as biological control methods to manage the species.


What’s The Difference Between Grasshoppers and Locusts?

There is something swarming in New Mexico. The infestation is so thick that clouds of insects are showing up on the radar like, well, real clouds.

“It is a nuisance to people because they fly into people’s faces while walking, running, and biking,” John R. Garlisch, extension agent at Bernalillo County Cooperative Extension Service, told ABC News. “They are hopping into people’s homes and garages, they splatter the windshield and car grill while driving, and they will eat people’s plants.”

So what are they? Well, news outlets are calling them grasshoppers, but if they’re swarming, does that make them locusts? A New York Times article from a similar occurrence last year went so far as to say that grasshoppers become locusts simply by swarming.

National Weather Service

In a 2010 article on locusts that was published in the Encyclopedia of Animal Behavior, Alexandre Vsevolo Latchininsky, Extension Entomologist for the State of Wyoming, explains that “all locusts are grasshoppers but not all grasshoppers are locusts.” He defines locusts as “short-horned grasshoppers (Orthoptera: Acrididae), distinguished by their density-dependent behavioral, physiological, and phenotypic polymorphism.”

The phenotype mutability refers to the fact that for some subspecies of locusts, the different stages of life are marked by different colors and even body shapes. However, it is the behavioral aspect—the mass grouping together—that is most notable. The act of swarming, or exhibiting a so-called “gregarious phase,” is the most obvious characteristic that identifies a subspecies of grasshopper as a locust.

Latchininsky explains in his paper that “out of more than 12,000 described grasshopper species in the world, only about a dozen exhibit pronounced behavioral and/or morphological differences between phases of both nymphs and adults, and should be considered locusts.” And in fact, the tendency to swarm together is a relatively recent phenomenon in grasshopper evolution.

However, what we have in New Mexico is an uncharacteristic swarming by members of the Acrididae family, which are the non-swarming members of the grasshopper designation. Latchininsky tells mental_floss that this has happened roughly a dozen times in evolutionary history. However, he cautions that, “these occasional gatherings do not mean that these grasshoppers are locusts! There are only a dozen or so true locust species in which the increase of density causes behavior changes followed by physiological, morphological and other phenotype changes.” Based on extenuating factors—last year’s monsoon season coupled with a dry winter—this current phenomenon seems to be a case of too many grasshoppers in too little space as opposed to a proclivity to swarm.

Still, Latchininsky speculates that it, “may be a first evolutionary step towards this species becoming a locust in a distant future.”


Difference between a Locust and a Grasshopper

People associate locusts with plagues and massive agricultural farm damage while grasshoppers spur childhood memories of playing in the field and Jiminy Cricket. However, these critters are basically the same except for one major detail. When is a locust not a grasshopper and vice versa? This article seeks to find out just that.

Summary Table

Locust Grasshopper
A grasshopper that belongs to the family Acrididae An insect that belongs to the order Orthoptera
Characterized by a behavior called swarming Usually solitary and does not swarm
Destructive; can cause plagues and large scale crop damage Cannot do much harm on its own


A locust belongs to a certain species of short-horned grasshoppers that are members of the family Acrididae and are characterized by a behavior called a swarming phase. These insects undergo behavioral and physiological changes (i.e. phase polyphenism) upon reaching a high level of population density. This is what differentiates a locust from a grasshopper – locusts swarm under certain conditions.

Locusts are harmless until they swarm. They are not a major threat to agriculture. However, in times of drought succeeded by fast vegetation growth, something happens to these innocuous insects. Serotonin in the locust’s brain starts a series of dramatic changes. They start to breed and grow exponentially. They become gregarious, forming a huge swarm of biblical proportions. Once the swarm is large enough, the locusts become nomads and somewhat migratory. The swarm moves around, stripping fields and causing damage to crops. Locusts travel great distances and consume green crops wherever their swarm settles.

American grasshopper

Grasshoppers belong to the order Orthoptera along with katydids (i.e. bush crickets) and crickets. Experts believe that grasshoppers are likely the oldest existing group of plant-chewing insects. Grasshoppers are believed to have been around for 250 million years, all the way back to the Triassic period. Their familiar, powerful hind legs allow them to escape from predators by catapulting themselves into the air with vigorous leaps.

Grasshoppers do not go through a complete metamorphosis as they hatch from their eggs as nymphs or “hoppers.” They shed their skin (i.e. molting) several times as they grow into adults.

Stridulation, or the distinct behavior in insects to rub their feet in order to produce a “singing” sound, forms a big portion of a male grasshopper’s daily routine. This is a way of communicating to others that it is healthy, sociable, and ready to mate. Female grasshoppers can stridulate as well, although the sound is nowhere near the male’s singing.

Grasshoppers are typically polyphagous, which means they consume vegetation from different sources. They usually eat grasses, primarily including cereal crops. However, there are some omnivorous species that eat animal tissue and feces.

Locust vs Grasshopper

So what’s the difference between a locust and a grasshopper? Locusts are members of the Acrididae family, a species of grasshoppers that have gone through behavioral and physiological changes. Grasshoppers, on the other hand, are insects that belong to the suborder Caelifera of the order Othoptera. They are considered one of the oldest plant-chewing insects and are not viewed as pests on their own. Locusts, in contrast, are considered pests that have been causing agricultural damage and famine throughout history.


When Weather Changes, Grasshopper Turns Locust

By Rachel Nuwer

    April 8, 2013

As recently as 1963, plagues of ravenous desert locusts could stretch across continents, blanketing lands from West Africa to India up to 14 years at a time. Today, with pesticides and early eradication efforts, such biblical swarms no longer occur. But as farmers in Sudan, Egypt, Israel and Saudi Arabia can currently attest, locust swarms remain a serious regional threat.

Locusts are grasshoppers that have evolved to undergo a sort of Jekyll-to-Hyde transformation, a result of sporadic patterns of rainfall.

After a particularly wet season, deserts bloom into life. Vegetation supports a growing population of thriving grasshoppers. When the rains cease, the leaves wither and the hungry insects begin congregating in the last patches of remaining plant life.

As the grasshoppers crowd together, something shifts. The insects, which normally live alone, begin bumping into one another. When grasshoppers touch one another’s hind legs, the contact sets off hormonal changes: The adults’ neutral brown coloring is replaced with a fearsome bright yellow, and they become “gregarious” group insects, coordinating their growth, behavior and egg laying. When the swarm devours all of the surrounding vegetation, it takes to the air, traveling up to 100 miles a day in search of its next meal.

“Take a swarm the size of Manhattan,” said Keith Cressman, a senior locust forecasting officer at the United Nations Food and Agriculture Organization in Rome. “In one day, that swarm will eat the same amount of food as 42 million people.”


No Comments

Leave a Reply

Your e-mail will not be published. All fields are required.