Your Guide to Locusts

What do Robert Louis Stevenson’s Dr. Jekyll and Mr. Hyde, the nematodes from cartoon classic Spongebob, the Bible, and Doctors Without Borders have in common? Locusts. Okay, hear me out.

But first, a quick outline

Click to jump to wherever you want to start reading from.

What Are Locusts? Where Do They Come From? 🦗
Locust Clustering Network Effects 👯👯👯👯👯
Are Locusts Harmful? ☠️
Do Locusts Eat Meat? 🍖
Why Do Locusts Migrate? 🏃
Locust Swarm Frequency 📈
Are There Any Tools to Detect Locust Swarms Early? 🕵️
Are Locusts Edible? 😋
But Are Locusts Kosher? 🤔
Locusts in Religious Texts ✝️ 🕉️
Responses to Locust Swarms: Human Activity and Natural Predators 📌
Chinese Duck Armies? History repeats itself! 🦆🦆🦆
Are locusts good for anything? ➕
Research Directions👨‍🔬

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What Are Locusts? Where Do They Come From? 🦗

Locusts are part of the Orthoptera (from Greek words: Orthos which is ‘straight’/’rigid’ and ptera which is ‘wing’) order. There are 7,000 species of grasshoppers but only 20 are classified as locusts. These species can be found everywhere except Antarctica.1 Most locusts generally live and are found in Eastern Africa and over time, have found their way into India, Pakistan, and even China.6 When you look at a single locust and compare it to a grasshopper, they’re not too different. However, one key difference between them is that locusts can exist in two different physical states, solitarious and gregarious. Locusts are most similar to grasshoppers when in the solitarious state.2  Physically, tan brown and green hues on a locust mean it’s solitarious. For a locust in this phase, there is no hive-mind. It’s not part of a swarm.  

Locust Clustering Network Effects 👯👯👯👯👯

However, when multiple locusts happen to be in close contact for a while, things start to change. In close proximity, the locusts brush up against each other more frequently. Their hind legs specifically take in mechanosensory contact from resulting in body changes to the gregarious state.3  In the absence of crowded conditions, these gregarious locusts can revert back to the solitarious phase again.4 A host of changes occurs when they become gregarious, with new behavioral changes taking just a few hours to surface. Physical changes follow after just days. Their color changes to a warning yellow and black, their body becomes smaller, their brains get bigger, and their shape and fertility changes too.5 It’s no wonder that at one time in the past, locusts in different phases were considered different species.2 This drastic change in physical appearance reminds me of Dr. Jekyll and Mr. Hyde

Are Locusts Harmful? ☠️

Locusts aren’t directly harmful in that they aren’t inclined to bite people.5, 6, 8  They don’t attack people or animals. In Eastern Africa and Yemen, locusts endanger food security for 42 million people.6, 8 India, Ethiopia, Kenya, Yemen and few others have been threatened by harvests attacking crops. Swarms can be so dense that even aircrafts need to get diverted.5, 15, 8 In this way, locusts can be harmful when they proliferate and run unchecked on unwitting crop fields, endangering the livelihood and food security of millions of people. 

Do Locusts Eat Meat? 🍖

Locusts don’t eat meat but they possess an appetite for crops like sorghum, teff and wheat. The affinity of these locusts for plants suggests they also need a source of protein. However, at least for South American locusts, it seems they prefer loading up on carbohydrates while shifting into the gregarious phenotype. 1, 5, 13

Why Do Locusts Migrate? 🏃

Once in the gregarious phase, locusts start to migrate. This makes intuitive sense because if they’re staying in one place, they’re probably going to run out of resources quickly. Director of the Global Locust Initiative at Arizona State University, Arianne Cease, says that “…there are too many of them and they would run out of food,” and so locusts migrate to find better resources. Locust swarms embody the phrase “strength in numbers.” They’re like different beasts in these different phases. For example, a single locust on its own may avoid plants with hyoscyamine, a toxic alkaloid, but gregarious swarm locusts find its smell intoxicatingly attractive.1,8,6

These swarms, once mobilized, will move without much opposition. Entomologist Hojun Song, in an email correspondence with Umair Irfan and Jen Kirby of Vox said, “Locusts do not honor political boundaries and can easily invade other adjacent countries.”*

*This little quote prompted me to make this wonderful little graphic on my phone. It was inspired by the Doctors Without Borders logo. How did I do it? Check the appendix at the end of this article for an explanation.

Original Image by Eashan Reddy Kotha – Titled: “Locusts Without Borders”

Locusts in the gregarious phase become devastating due to sheer volume. How are they so prolific? To understand that, it’s important to take a look at factors affecting the locust life cycle. Weather and other environmental conditions are two such factors that affect desert locust lifespan.6 Generally, lifespan ranges from three to five months. The three stages of a locust’s life are the egg, then hopper, then adult.6 Locusts don’t go through a pupal stage like butterflies do when developing. They undergo what’s known as incomplete or direct metamorphosis and thus, look similar to adults while growing. 

Locust eggs take about two weeks to hatch on average. Hoppers become adults over thirty to forty days but this varies from species to species. Differences in temperature/habitat conditions also influence the range. Hoppers and adult locusts are ectotherms as they regulate body temperature by either moving to shady areas or into sunlight to maintain a stable temperature.2  The hopper stage can be divided further into stages called instars with a moult occurring between each instar. 

Picture shows a circular depiction of a locust moving from egg pod through instar stages to adulthood.

Image courtesy of the Desert Locust Control Organization for East Africa

With each successive moult, wings start to develop and grow bigger on the hopper. The final moult is called fledging. For the most part, juveniles look similar to the adults.2 The hopper or nymph stage is the key to locust swarm prevention because at this stage, they haven’t developed wings.1 After they enter adulthood, the locusts become significantly harder to deal with. They’re young, mobile, and hungry. Senior locust forecasting officer at the Food and Agriculture Organization (FAO), Keith Cressman likened them to “hungry teenagers” with a “voracious” appetite.1 Adults mature from two to four months.6 About a month into adulthood, by the time the locusts have eaten through nearby agricultural fields, they lay more eggs. This escalates the locust problem dramatically because there is a 20-fold increase with every new generation.6

A 20-fold increase is nothing to sneeze at. Again, how is this even possible? How do locusts reproduce? It starts when the male locust mounts the back of the female, applies the tip of his abdomen to hers and passes sperm into the reproductive tract.7 The sperm sac in the female abdomen stores the sperm, and once the eggs travel through the oviduct during laying, the sperm is released to fertilize them.7

The females lay eggs about 10-15 cm below the surface by using the ovipositor at their abdomen tip.6 Solitarious females lay anywhere from 95 to 158 eggs in a single pod and gregarious females lay slightly fewer than that.6 The pod is covered in a froth that helps protect the eggs from drying out, getting eaten, or becoming disease ridden.2 Now consider that in one square meter, there can be up to 1,000 egg pods. Individual locusts aren’t so much a problem as swarms that number in the billions over hundreds of thousands of acres. This is a plague of a Biblical scale. 

Those thousands of laid eggs are a precursor for nearly 150 million locusts per square kilometer (600,000/acre).5  A singular locust may not be an issue to a large field of crops, but when each locust eats its own weight in plant matter per day, 150 million is enough to devour the equivalent food supply of 35,000 people per day.5,6 And if you were wondering if all that eating makes them lazy and unable to travel far, here’s some news: swarms can travel from 90 to over 100 miles in a single day, riding the wind like dandelion seeds.1, 8 These locusts are also very prepared to handle higher temperatures and drought conditions. Experiments by The Global Locust Initiative have shown that Australian plague locusts could survive without water for up to a month. This means that in time, locusts will be able to further expand their operations to wider ranges. 

Locust Swarm Frequency 📈

Locust swarms aren’t a consistent phenomenon. Sometimes, years to decades can occur between them. However, climate change has resulted in ripe conditions for these swarms to propagate.5 According to CBS News, locusts usually arrive in India from Pakistan in the summer months up to autumn (July-October).8 While historically, the swarms have been generally contained to Rajasthan, climate conditions have facilitated spreading into other states. Warm weather correlates with more locusts.8  

Heavy rainfall is a key variable. The Indian Ocean Dipole is a phenomenon that occurs when the Eastern and Western side of the Indian Ocean alternate between warmer and colder temperatures. Recently, increased evaporation due to a stronger temperature gradient led to downpours in India and East Africa. Dr. Koll, a scientist from the Indian Institute of Tropical Meteorology claimed the warmer waters in 2019 resulted in greater rainfall.8 The downpours which forced evacuations, allowed for a vegetation boom. Heavy rains in May 2018 were enough to stimulate plant growth for six months in the southern Arabian Peninsula.1 That duration of time is enough for two generations worth of locust growth. That’s about a 400-fold surge. This abundance of plant matter made it favorable for locusts to swarm and breed rapidly. The limiting factor for their growth, removed. Some of the egg pods that hatched may have been new but there were also dormant locust eggs laid in prior cycles that were kick started by the rain. The locusts, in their hopper stage (also known as nymphs), start to chow down on the available greenery and if not kept in check, will aggregate into gregarious swarms.5 Another side to the problem with the 2020 locust swarms is posed by the deputy director of India’s Locust Warning Organization, K.L. Gurjar: “…the attack is by very young locusts who fly for longer distances, at faster speeds, unlike adults in the past who were sluggish and not so fast.” 1, 9 

Long term climate change has been making more extreme Indian Ocean Dipole events common, meaning locust swarms could become more and more common in the future. The World Meteorological Organization has also expressed concerns over higher-than-average temperatures.10 This frequent occurrence would create even greater food insecurity. The FAO has stated that over 20 million in the East Africa region have faced severe food insecurity. 135 million already face starvation, with another 130 million more at risk according to the World Food Program. 17 million people in Yemen are already at risk of famine because of locust issues and conflicts. A Turkana pastoralist, in an interview with the Guardian, said that as these scarcities increase, there’s likely to be more resource-based conflict in grassy areas.5, 17  We must also consider the displacement effects of farm workers with ravaged fields. Labor opportunities are likely to be scarce and the economic pressure of events result in further hardships for those seeking relief and opportunity. In a word, locust swarms are just like those nematodes in that one Spongebob episode

As expected, the chance occurrences of these swarms makes it difficult for countries to prioritize and allocate resources towards the threat. Another consideration is that these swarms are meant to be caught early to be prevented. They start up in remote spots with minimal human supervision. As a result, locust propagation may occur without people knowing and hit a threshold that becomes too hard to manage and there’s a runaway effect. 

Thus, locust detection and prevention in its current form is largely a feet-on-the-ground game and the local governments in these areas aren’t always prepared to play it. Other global issues such as pandemics complicate the ability of these governments to respond after the fact and scale up an effective response. Senior locust forecasting officer of FAO, Keith Cressman and his team likens locust plagues to wildfires in his interview with Wired.1 The team can model and predict locust distribution a month in advance and coordinate efforts with the endangered countries to get pesticides ready, set up drones, and recruit people to kill locusts.1 Lockdowns and social distancing, coupled with the issue of strained supply chains are all free spaces on the locust propagation Bingo card. “Ultra-low volume” pesticides are the first line of attack on the budding locusts.5 These rely on physical contact with the locusts themselves in order to affect them. Thus, it’s not enough to just crop dust fields from a distance with them. While locust control teams have been granted essential service status, curfews limit their efficacy in places like Kenya. 

India has been scrambling to respond to the locust swarms, using drones to track the crop destroying insects. The spread has affected Rajasthan, Gujarat, Maharashtra, Madhya Pradesh, Punjab, and Uttar Pradesh states.8 Conflict zones such as the Middle East are further mired by the issue because coordinated control efforts are harder to put together, further increasing the danger of food insecurity. The fact that locusts are highly mobile presents another issue because unlike the hoppers, locusts can affect whole regions. A swarm in the Middle East, if not controlled could rain devastation in East Africa. Sure, a quick response in one location could help that one location but ultimately, it doesn’t offset the responsibility for locust control in the nearby regions. 

Keith Cressman: “For the last two years we have not seen any single break in the weather for desert locusts,” Cressman said. “It’s just been phenomenally favorable to them.”

Are There Any Tools to Detect Locust Swarms Early? 🕵️

Locusts are a bother when they start to move. However, some tools that have been developed and are being tested in order to help detect early signs of locust swarms. NOAA has retrofitted existing tech that tracks wildfire and volcano plumes into an app  for the FAO.10 The app is modeled after NOAA’s HYSPLIT dispersion model and utilizes wind pattern forecasts to track movements of the passive flying desert locust. The technology has been employed in the past to track the plumes from other large motions like wildfires or volcanic plumes. Scientists expect to upgrade functionality and reliability in the coming years because in its current form, there’s no way to “incorporate locust breeding patterns” according to NOAA lead scientist, Mark Cohen. The app is currently exclusive to FAO. However, the hope is that the tool will be an improvement over the prior method of identifying locust spreads, that is, via satellite monitoring and reports from people on the ground.10

Are Locusts Edible? 😋

Yes, locusts have been eaten in the past for many reasons. Marketplaces with heaps and heaps of dead locusts are common in those countries.6  They can be roasted, boiled, stir-fried, or dried for eating later. They taste like a mix between prawns, toasted sunflower seeds and chicken schnitzel. In terms of nutritional value, proteins comprise 62% of the dry weight of an adult desert locust. Locusts contain many other trace elements (Si, Cu, Fe, Na, K, Mg, Ti, Ni, P, and S).6, 14 

But Are Locusts Kosher? 🤔

While insects generally aren’t considered so, locusts are kosher.11 Unfortunately, you generally can’t really eat your way out of a locust invasion. Heavy insecticide use means that they could be contaminated. Tainted protein isn’t so appetizing when it comes down to it. Israel is one such place that faces this issue with converting dead locusts into a food source.

Another consideration is that harvesting locusts as a protein source is a bit unviable due to the climate conditions required for it. The linked Times of India article goes into further math as to the potential of breeding locusts as a food source.12 The math is based on the pricing 1.32 dollars per kilogram for chicken and extrapolates that to hundreds of thousands of dollars worth of product. 

For the sake of being thorough, let’s work out the napkin math. An average locust weighs 2 grams and a swarm can range from 100,000 to 200,000 tons. That means that on the low end, we’re looking at 90,718,474 kg and on the high end, 181,436,948 kg. This means the total value ranges from $119,748,386 to $239,496,771.36 in USD. 

Locusts in Religious Texts ✝️ 🕉️

In the Time of India article and other local news reports, interest in the Bible increased as the locust swarms tore through the country. Questions like “Who ate locusts in the Bible?” spiked on the Google Trends search. The oft referenced passage about locusts is provided below. There was also mention of how ancient Sanskrit poetry mentions locust plagues but I couldn’t find any legitimate source for that.

And the same John had his raiment of camel’s hair, and a leathern girdle about his loins; and his meat was locusts and wild honey.

Responses to Locust Swarms: Human Activity and Natural Predators 📌

A common sight amongst communities dealing with locust swarms includes locals making loud noises, banging on pots and pans and clanging other metal objects in strained cacophony to drive away the locusts. Actions include drumming on rooftops, and running into cars to jam their car honk to drive locusts away. Some whistle, some throw stones, and others light fires (reminiscent of prescribed burns) to smoke the locusts out.15, 9 

Locusts have many predators such as ducks, chickens, and other mammals. However, there aren’t any specific locust-exclusive feeders so their impact on locust populations in an outbreak is minimal. The problem lies with scale because the predators can’t scale up quickly enough to feast on the sudden increase in locusts and the result is a replenishing pot effect, where the predators are sated and the locusts continue to reign. There are some birds that do feed on high density locusts, however. 

Chinese Duck Armies? History repeats itself! 🦆🦆🦆

There are many ways to control locust populations but perhaps the most amusing one has to be China’s duck army. In 2020, it was claimed that at least 100,000 (not a typo) ducks were to be sent to Pakistan as part of a test of locust control. Lu Lizhi, a senior researcher with the Zhejiang Academy of Agricultural Sciences in a telephone interview with Bloomberg said “one duck is able to eat more than 200 locusts a day.”14 Chickens could eat up to 70 locusts a day, making them more suited for small scale plagues.11,16 However, considering the logistics of the operation, China Agricultural University professor, Zhang Long denied the reports.17 

In Pakistan, local farmers are being incentivized to capture, kill and turn locusts into chicken feed. The idea was thought up by Dr Muhammad Khurshid, a PhD in natural resources management and former civil servant in the Ministry of National Food Security and Research. He says the idea was modeled after a similar initiative in Yemen when it was dealing with locusts in 2019. According to Johar Ali, a biotechnologist, they found that “the best time to catch locusts was between 10pm and 8am.” The initiative appeared successful as 25 tonnes of locusts were reeled in in just four days. Mothers, fathers, and children alike were part of the effort. Manual hunting for locusts also reduces pesticide use. Since locusts have such a high protein composition, they could be used as an alternative to soybean exports which only comprises 30-45% protein content. Apparently, it’s also cost effective compared to soybeans. It takes .39 USD per kg (30 INR per kg) to dry and mill locusts while soybeans are .70 USD per kg.

To a lesser extent, fungi, bacteria, and viruses play a role in curbing locust numbers. The limit of their effect is largely due to the arid temperatures in which locusts aggregate in. However, Metarhizhium acridum is a fungal strain that can attack locusts…but how? It works because the fungus can survive in high temperatures. Its method of action is through breaching the locust’s cuticle and infecting the cell layers within it resulting in system wide problems.18, 19,20 This biopesticide was made by CSIRO and has been used since 2001.  According to the Australian government, there has been a precedent of bacterial infection leading to mass mortality of locusts. An infestation in the vegetation in New South Wales in Spring 2010 was determined to be the cause.

Are locusts good for anything?

According to the FAO, locusts have been used for healing rituals and they can be useful because of their nutritional value. In the Philippines, locals soak locusts in coconut oil and later apply the oil to wounds or sprains. Locusts also make for good feed for animals and fish.11 We also mentioned before how there were initiatives to hunt and capture locusts without using pesticides in order to use them for animal feed and as a human food source. 

Extra Note: When Australia was hit by swarms in 2004, they were re-branded “sky prawns” to encourage people to eat, or at least control, them.11

Research Directions

The scientific field has been making strides towards understanding locust development in order to better deal with them. For example, a 2015 review investigated epigenetic mechanisms in locusts. 21  Part of the effort was to determine if there were any epigenetic mechanisms that could result in the transition of locusts from solitarious to gregarious phases and vice versa. This is a field with great opportunity because the earliest epigenetic studies on locusts were in 1951 and nearly 60 years passed between that time and the next discovery. RNA interference could be used to knockdown genes in locusts. However, scientists have been unsuccessful in using RNA interference to completely knock out target genes.21  Epigenetic research remains a promising means of studying locust phase transition. The Australian plague locust for instance, can change phases rather abruptly between generations. The review cites a study done by (Guo et al. 2013) which indicates that serotonin injections into gregarious locust head cavities resulted in behavioral shifts towards becoming solitary. This suggests that serotonin is one factor that is involved in the locust phase change. Overall, locusts have only recently been subjected to improvements in genomics but newer studies could help shape our understanding at the molecular level.22 RNA-Seq analysis has made it possible to determine gene differences between the solitarious and gregarious locust phases. These external changes in locusts as they shift from phase to phase are due to changes in the central nervous system. Gene overexpression is common in the gregarious phase because they need to be more active, metabolize more food, and undergo physical changes. It makes sense for these genes to be overexpressed. Higher protein production along with greater molecule turnover would correlate with higher gene expression.22  Environmental factors such as stress and mechanosensory stimulation result in changes at the genomic level. Those gene expression changes mean that as the locust moves from one phase to the other, the products of that expression lead to the other observable physical changes we’ve discussed. 

The FAO has called the desert locust “the most destructive migratory pest in the world.”10  The issue with locust swarms clearly underscores the need for not only research into the problem using genetic and biological tools but also behavioral and carefully designed epigenetic studies. We also need to create initiatives to address climate change through policy and initiative. That way, individuals wouldn’t have to suffer from future locust swarms. 

Some questions that come to my mind after doing all this reading are related to locust brains. We know that they change size as they shift from phase to phase. However, how are those brains being used in one state versus the other? Imagine if gregarious locusts were actually forming a sort of mind network that links them together and allows them to stay relatively coordinated as they ride the winds into the countryside and farmlands. Network effects strike again!

If you enjoyed reading this and would like to explore more about locusts. Check out these interesting papers on how temperature affects them. Find those here and here

Author’s Note: As I added the final touches on this fairly big piece of writing, I realized something else. Cicadas exist. How could I forget? And yet, I had. Maybe I’ll cover that topic another day. They are eerily similar to locusts but have definitive differences. While locusts tend to be more of a problem in Africa/Middle East/South Asia regions, periodical cicadas are ready to descend on the United States’ East coast in 17 year cycles. Millions of them. Yeah, I know.

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Appendix

Mechanosensory: physical movement of sensory organs like hair results in a neural signal being sent to the brain. 

Incomplete/Indirect Metamorphosis: Basically they don’t go into a cocoon like butterflies do but they start out looking like really small adults and then grow proportionally bigger into adult size and develop other things that indicate maturity like wings in the case of the locust. 

Ovipositor:  Tube-like organ used by some animals for the laying of eggs.

If you’d like more words to be defined properly, let me know on Twitter! (@eashankotha)

How did he do it?

Inspired by Doctors Without Borders; drew outline of a locust, then drew a red marker layer that looked similar in color/form to the Doctors Without Borders swoosh. Erased from the marker layer to create the outline of the locust through the white space. Used Instagram to tack on the text, all caps to emulate a similar style to the presentation of the logo.

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