Scientists raise concern as eerie phenomenon spreads across US coastlines: 'We're about 50 years behind'
The Chesapeake Bay has taken on a haunted appearance. Our overheating planet is helping turn the region into a graveyard for cedar and pine trees, per Knowable Magazine.
As the world warms, driving sea levels higher, saltwater is encroaching along the world's coasts and into its estuaries. The seawater invasion can overtake the freshwater that gives life to deciduous trees. It is happening in the Chesapeake Bay, and it isn't going unnoticed. Scientists released a report on the salinization that is impacting coastal ecosystems.
"The impact of saltwater intrusion on coastal forests and farmland is typically understood as sea-level-driven inundation of a static terrestrial landscape, where ecosystems neither adapt to nor influence saltwater intrusion," according to a study conducted by an international team of scientists. "Yet recent observations of tree mortality and reduced crop yields have inspired new process-based research into the hydrologic, geomorphic, biotic, and anthropogenic mechanisms involved."
"When a lot of these forests die back, instead of being replaced with a native salt marsh ... what's actually taking its place is a phragmites marsh," University of Maryland Eastern Shore in Princess Anne forest ecologist, and coauthor of the Annual Review of Marine Science article, Stephanie Stotts, told Knowable Magazine.
The Minnesota Aquatic Invasive Species Research Center describes phragmites, also known as common reed, as "a tall, densely growing perennial grass that can take over large areas, displacing native vegetation and reducing habitat quality for fish and wildlife."
Trees die slowly; sometimes, it takes several decades for them to perish. It will take a long time for us to see the full consequences of these lifeless forests. "We're about 50 years behind," said Stotts, per Knowable Magazine.
Ghost forests are the remains of a once-vibrant woodland ecosystem that has succumbed to the poisoning of encroaching saltwater. Forests have morphed into marshes during prior periods of rising sea levels. Scientists point out that marshes have some positive attributes. They are home to oysters, clams, shrimp, and certain bird species.
The problem with ghost forests is that they can disrupt the carbon cycle. In other words, forests absorb more carbon pollution from the atmosphere than they release. After trees die, they can eventually contribute to the heat-trapping gases in the atmosphere, fueling even more warming.
Living trees can also act as a buffer to storms. Ghost forests increase the vulnerability along coastlines to erosion and storm surge. While extreme weather events have always existed, experts have found that the human-induced climate crisis supercharges these events, putting our communities in even more danger and devastating ecosystems.
The saltwater encroaching along the world's coastlines is accelerating as our overheating planet drives rising seas. Moving away from dirty energy sources to renewable options will help cool our planet and reduce the rise in sea levels.
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Yahoo
08-05-2025
- Yahoo
Scientists raise concern as eerie phenomenon spreads across US coastlines: 'We're about 50 years behind'
The Chesapeake Bay has taken on a haunted appearance. Our overheating planet is helping turn the region into a graveyard for cedar and pine trees, per Knowable Magazine. As the world warms, driving sea levels higher, saltwater is encroaching along the world's coasts and into its estuaries. The seawater invasion can overtake the freshwater that gives life to deciduous trees. It is happening in the Chesapeake Bay, and it isn't going unnoticed. Scientists released a report on the salinization that is impacting coastal ecosystems. "The impact of saltwater intrusion on coastal forests and farmland is typically understood as sea-level-driven inundation of a static terrestrial landscape, where ecosystems neither adapt to nor influence saltwater intrusion," according to a study conducted by an international team of scientists. "Yet recent observations of tree mortality and reduced crop yields have inspired new process-based research into the hydrologic, geomorphic, biotic, and anthropogenic mechanisms involved." "When a lot of these forests die back, instead of being replaced with a native salt marsh ... what's actually taking its place is a phragmites marsh," University of Maryland Eastern Shore in Princess Anne forest ecologist, and coauthor of the Annual Review of Marine Science article, Stephanie Stotts, told Knowable Magazine. The Minnesota Aquatic Invasive Species Research Center describes phragmites, also known as common reed, as "a tall, densely growing perennial grass that can take over large areas, displacing native vegetation and reducing habitat quality for fish and wildlife." Trees die slowly; sometimes, it takes several decades for them to perish. It will take a long time for us to see the full consequences of these lifeless forests. "We're about 50 years behind," said Stotts, per Knowable Magazine. Ghost forests are the remains of a once-vibrant woodland ecosystem that has succumbed to the poisoning of encroaching saltwater. Forests have morphed into marshes during prior periods of rising sea levels. Scientists point out that marshes have some positive attributes. They are home to oysters, clams, shrimp, and certain bird species. The problem with ghost forests is that they can disrupt the carbon cycle. In other words, forests absorb more carbon pollution from the atmosphere than they release. After trees die, they can eventually contribute to the heat-trapping gases in the atmosphere, fueling even more warming. Living trees can also act as a buffer to storms. Ghost forests increase the vulnerability along coastlines to erosion and storm surge. While extreme weather events have always existed, experts have found that the human-induced climate crisis supercharges these events, putting our communities in even more danger and devastating ecosystems. The saltwater encroaching along the world's coastlines is accelerating as our overheating planet drives rising seas. Moving away from dirty energy sources to renewable options will help cool our planet and reduce the rise in sea levels. Do you think America has a plastic waste problem? Definitely Only in some areas Not really I'm not sure Click your choice to see results and speak your mind. Scientific studies can help illustrate how the buildup of heat-trapping gases in our atmosphere is impacting our planet, but getting the word out by exploring critical climate issues and talking to family and friends about them to raise awareness is important. So is supporting politicians who are fighting for the future of our planet. Join our free newsletter for good news and useful tips, and don't miss this cool list of easy ways to help yourself while helping the planet.
Yahoo
10-04-2025
- Yahoo
Everything you need to know about bird flu
In early 2024, the bird influenza that had been spreading across the globe for nearly three decades did something wholly unexpected: It showed up in dairy cows in the Texas Panhandle. A dangerous bird flu, in other words, was suddenly circulating in mammals—mammals with which people have ongoing, extensive contact. "Holy cow," says Thomas Friedrich, a virologist at the University of Wisconsin–Madison. "This is how pandemics start." This bird flu, which scientists call highly pathogenic avian influenza, or H5N1, is already at panzootic—animal pandemic—status, killing birds in every continent except for Australia, Knowable Magazine explains. Around the world, it has also affected diverse mammals including cats, goats, mink, tigers, seals and dolphins. Thus far, the United States is the only nation with H5N1 in cows; it's shown up in dairies in at least 17 states. In all of known history, "This is the largest animal disease outbreak we've ever had," says Maurice Pitesky, a veterinary researcher at the University of California, Davis. The virus, which emerged nearly three decades ago, is now creating upheaval in the poultry and dairy industries and making economic and political waves due to the fluctuating price of eggs. But there's more at risk here than grocery-store sticker shock. As it has journeyed around the world on the wings of migrating birds, the virus has infected more than 960 people since 2003, killing roughly half of them. Since the start of 2024, it's infected dozens of people in the United States—mainly farm workers—and it killed its first person stateside in January of 2025. So far, H5N1 flu hasn't acquired the key trick of passing with ease from person to person, which is what could enable a human pandemic. For now, both the U.S. Centers for Disease Control and Prevention and the World Health Organization rate the public health risk as low. But the situation could change. "The thing about this virus is, every time we think we know what's going to happen, it does something totally unexpected," says Michelle Wille, a virus ecologist at the WHO Collaborating Centre for Reference and Research on Influenza in Melbourne, Australia. "And that's the only consistent thing I can say about it." Biologically, H5N1 isn't so different from any other influenza A virus—the type that resides mainly in wild birds, as well as bats, and has occasionally jumped into human populations. It contains eight pieces of genetic material encoding 11 known proteins. Two proteins, the "H" and the "N" ones, stud the virus's exterior. H stands for hemagglutinin: It sticks to a cell's sugars so the virus can gain entry. N is for neuraminidase: It allows newborn viral particles to exit the cell. But there's lots of possible variety. The influenza A virus has at least 19 options for the H protein and 11 for the N protein, most of which are present in the various flu strains infecting wild waterfowl. H5N1 flu has version 5 of the H protein and version 1 of the N protein. There are also variants for the other genes. If two different flu viruses meet in a cell that they've both infected, they can swap genes back and forth, creating new kinds of flu offspring. Thus, all sorts of influenza A viruses infect the guts of wild waterfowl, usually without harm to the birds. But the viruses can cause trouble if they move into other creatures. A few decades ago, scientists thought they had a handle on what would happen if some bird influenza A virus spilled over into other species. In domestic poultry, it could turn nasty, but it was generally a "one-and-done" situation, says Bryan Richards, emerging disease coordinator at the U.S. Geological Survey's National Wildlife Health Center in Madison, Wisconsin. What happened in past instances was that all the farm birds would die, the virus would run out of hosts—the end. And the leap from birds to humans is not easily made. Scientists had long assumed that to infect people, an avian influenza A virus would have to trade genes with another virus in an intermediate species, like a pig, to adapt to mammalian biology. So back in 1996, when domestic geese in Guangdong province, China, came down with H5N1, it was hardly cause for worldwide alarm. But a year later, in Hong Kong, a 3-year-old boy died after suffering high fever and pneumonia. It took experts from around the world three months to identify the virus. At first, no one believed it was H5N1, says Robert Webster, a virologist and emeritus professor at St. Jude Children's Research Hospital in Memphis, Tennessee, who led one of the teams that made the ID. A virus with an H5 was supposed to be a chicken virus. But this H5N1 infected 18 people and killed six of them. "This was a nasty bastard," says Webster. Webster and other experts descended on Hong Kong, where they protected themselves by inhaling inactivated H5N1 virus obtained from that first case, as Webster recounts in the Annual Review of Virology. They learned that the boy's family had visited a live bird market, and testing identified more H5N1-infected birds in those markets and on farms. It had apparently arrived in ducks from China. "What blew everyone's mind, in 1997, was that humans clearly got infected with the avian virus, skipping the pig step," says Friedrich. Hong Kong killed all the poultry. That particular viral lineage was snuffed out. But its parent, back in mainland China, remained. And the vast viral lineage it spawned would continue to defy scientists' expectations. "This wasn't the one-and-done," says Richards. "The virus keeps throwing curveballs." H5N1 spread from farm to farm. It continued to infect people, usually those in very close contact with their domestic birds. Then, in 2005, the virus lobbed another curveball: It spilled back into wild birds, by now in a form altered enough to be deadly to them—killing thousands of bar-headed geese, gulls and great cormorants in China's Qinghai Lake Nature Reserve. "That," says Richards, "set the stage for where we are today." More birds, likely both wild and domestic, brought H5N1 into Europe and Africa. Through genetic mixing and matching, H5 hooked up with other partners, like N8, for a time. In late 2014, migratory birds brought H5N8 from Asia to the Pacific Coast of North America, where H5 also hooked up with an N2, and the outbreak spread across several states before fizzling out. The virus continued to spread in Asia, Europe and Africa, usually as H5N8, with a bit of H5N6. In 2020, reports of H5-containing virus infections in wild and domestic birds started to rise. A new variant of the H5 gene, called 2.3.4.4b, was first spotted in the Netherlands. Viruses carrying this H5 seem to have a particular ability to cross over and infect mammals, says Friedrich. By 2021, the 2.3.4.4b variety of H5 was back with a form of N1. "From there, we started seeing this mass spread event," says Wille. The virus arrived in North America in late 2021, this time to stay. The panzootic had begun. As birds migrate south for the winter, they bring H5N1 to poultry farms. Most infected chickens will die, and the primary defense is culling. In the U.S., more than 166 million chickens have been culled since 2022, though a lull in cases led egg prices to drop in early March 2025. To prevent spread, biosecurity has become the key watchword. For poultry farmers, that means a variety of things such as limiting human interaction with flocks, washing hands and boots, and wearing face masks. But the virus just keeps spilling over from wild birds into farmers' flocks. Part of the problem, Pitesky says, is that poultry farms are often located near water sources, like lagoons and rain ponds, where migrating birds roost overnight, putting wild and domestic animals in close proximity. It's a gut virus in wild birds, and it spreads easily through their feces. In February 2025, the U.S. Department of Agriculture announced allocation of up to $1 billion in additional funds to combat highly pathogenic avian flu, including support for biosecurity, financial relief for farmers and vaccine research. Companies have designed bird vaccines against H5-containing highly pathogenic avian influenza for a couple of decades, updating them as the virus evolved. The USDA announced in January 2025 that it would update its stockpile of vaccines for chickens, and Zoetis of Parsippany, New Jersey, recently created an updated version. It's based on a strain that was circulating in 2022 and has continued to do so, says senior vice president for global biologics research and development Mahesh Kumar, who works in Zoetis' Kalamazoo, Michigan, facility. The vaccine is effective at preventing symptoms and death, but does not prevent infection or viral transmission, Kumar says. Zoetis' past vaccines have been used in a handful of other nations for poultry and one even was used by the US Fish & Wildlife Service to protect California condors in 2023. In early 2025, the USDA granted Zoetis a conditional license for that new formula, but this preliminary licensure is just a step along the way to use, not permission to market or sell the vaccine widely. In fact, the US has never allowed widespread poultry vaccination for highly pathogenic avian flu, though poultry receive a number of other vaccines. There are concerns that vaccination could push the virus to mutate faster. But the big issue blocking vaccination is that doing so could limit international poultry trade, and the U.S. is a major exporter of live poultry. A vaccinated animal could carry the virus without symptoms, and many nations don't want birds that might be invisibly carrying H5N1. To get around that problem, Zoetis' vaccine has a twist. In preparing inactivated virus, the scientists used the N2 neuraminidase, instead of the N1 that H5 has recently buddied up with. That provides a way to check whether birds have antibodies that would indicate they've been exposed to the vaccine's N2, to the real virus's N1, or to both. Still, it is uncertain whether the U.S. would ever broadly deploy an avian flu vaccine. Pitesky says that much of the power rests with farmers who raise broiler chickens for meat and export; broilers make up about two-thirds of U.S. poultry sales. If the broiler farmers aren't on board, he believes it's unlikely the USDA would promote vaccination. The decision might end up being made at a state-by-state level, depending on regional poultry industries, suggests Rocio Crespo, a veterinary researcher at North Carolina State University in Raleigh. Kumar says Zoetis could turn stockpiled materials into ready-to-use vaccine in two months or less, depending on how close to finished form the vaccine is in storage. "We want to be ready," he says. And now the poultry industry's catastrophe has become the dairy industry's problem, too. The virus's 2024 appearance in Texas dairies was a surprise for flu experts: "The literature suggested that dairy cows don't get influenza A's," says Pitesky — but, "as the joke goes, cows don't read the literature." Dairies were caught off guard, without the guidelines and support systems that exist for poultry. And according to some reports, they've been slow to adopt biosecurity measures. Cows infected with H5N1 usually survive, though they must be taken out of the regular population and spend weeks in a hospital barn. Inflammation in their udders, or mastitis, turns their milk thick and yellowish; splashes of contaminated milk in the milking parlors create potential for the virus to move from animal to animal. (One study suggested that more widespread or respiratory infection does not occur, and there's no sign yet that beef cattle have been affected.) The USDA now requires the 48 contiguous states to test milk for H5N1. That testing identified two new spillovers of H5N1 into dairy herds, in Nevada and Arizona, reported in February of 2025. And, worryingly, that virus was a different version than the one that infected cows in 2024. That 2024 spillover featured an H5N1 with a particular collection of flu gene sequences, still H5 2.3.4.4b, called B3.13. But flu viruses evolve rapidly, and that H5 2.3.4.4b has shuffled genes with other viruses more than once, creating lots of variants and subvariants. More recently, another variant called D1.1 has been spreading in wild birds. While B3.13 still accounts for most cattle infections, it's D1.1 that hopped into dairies in early 2025. The long-term implications for cattle of D1.1, and avian flu in general, aren't yet clear. "We're really hoping this has just been a unique set of circumstances and that we don't get any more spillover events," says Jamie Jonker, chief science officer of the National Milk Producers Federation in Arlington, Virginia. But, he adds, "we'd like a vaccine to be in the toolbox and to understand how it can be used." Zoetis and other companies are working on H5N1 vaccines for cows, though it's too soon to know if and how such vaccines would be deployed. Even with vaccines, though, "we may not be able to put out this fire," says Gregory Gray, an infectious disease epidemiologist at the University of Texas Medical Branch at Galveston. "It appears, to many of us, that these viruses are going to be endemic, or we say 'enzootic,' for a long time." What kind of risk does all this pose for people? Gray has studied a number of viruses in cattle and other animals, and he says that while spillovers from one species to another are common, it's rare that a virus adapts to spread easily in the new species. As of spring 2025, there are no confirmed cases of human-to-human H5N1 transmission in the United States. "It's not like in the movies," Gray says. "It's going to take continual spillover events for it to get a foothold." But it can happen, as it did in 2009, when an H1N1 influenza A virus with a novel mix of genes jumped from pigs into people, where it then spread widely. This caused a pandemic, killing an estimated 123,000 to 203,000 people worldwide, a death toll grossly eclipsed by the more than 7 million who died of Covid-19. To become adept at infecting humans, the virus would have to change the structure of its hemagglutinin. Its current version sticks to a specific arrangement of sugars on the surface of bird cells. The birdlike sugar arrangement is found in cow udders, explaining the mastitis. Humans do have this birdlike sugar arrangement, but it's buried deep in the lungs, making the virus hard to catch and hard to spread to another person. It's also present in human eyes, which could explain why pinkeye was the most common clinical sign in people who caught bird flu in the U.S. in 2024 (many also experienced fever and respiratory symptoms). But for ongoing person-to-person transmission through coughs, sneezes and sniffles, researchers think H5N1 would have to mutate to recognize a sugar arrangement found in the human upper respiratory tract—the nose, nasal cavity, sinuses, mouth, throat and voice box. It would also have to make changes to the protein that copies its genes, the viral polymerase. This polymerase would need to switch from working well with bird proteins to working well with human ones. It has done that, to some extent: Some versions of H5N1 have acquired relevant mutations that help it replicate in mammal cells. But as of spring 2025, none of the viruses that have jumped from cows to humans have hemagglutinin mutations that are predicted to support person-to-person transmission, Friedrich says. H5N1 could either evolve on its own, or trade genes with another human-infecting flu. The latter possibility is particularly concerning at times of high rates of seasonal flu, such as during the 2024-25 winter. The more flu virus floating around, the more chances for two kinds to meet in the same cell in the same animal and exchange genes, to birth something new and potentially dangerous. Factors beyond the virus itself influence pandemic risk, too. "There are a lot of things that have to align, not only on the virus side, but also on the people side," says Valerie Le Sage, a virologist at the University of Pittsburgh who cowrote an overview of barriers to flu transmission in the 2023 Annual Review of Virology. One of them is disease history. From recent experiments with ferrets, which get and transmit the virus similarly to the way people do, Le Sage suspects that people who've had flu before—that's most people over the age of 5—might have enough immunity to stifle the worst consequences of H5N1 flu. In her experiments, ferrets earlier exposed to the 2009 H1N1 swine flu were protected from the worst symptoms and death when later exposed to H5N1 from Texas cattle. Ferrets that were just given H5N1 flu got sick and died. "I can't tell you exactly how long this protection lasts, but it is nice to see," says Le Sage. Also good news is the observation that the virus isn't hitting anywhere near the reported 50 percent mortality rate in recent U.S. infections. Such rates are imperfect calculations, Friedrich notes, as they are based on people who were sick enough to get tested for H5N1; people who didn't get very ill would not be tallied as survivors. That would artificially inflate the death rate, though it's unclear how much this has affected calculations. Asymptomatic infections may not be uncommon, at least in current U.S. cases: A recent CDC study found that three dairy veterinarians had antibodies to H5N1, indicating they'd been infected, but had never noticed symptoms. The other gene variants that H5N1 has acquired also seem to be a factor, and here the news may be less good. The earlier B3.13 virus seemed to cause mild infections, says David Hamer, a public health epidemiologist at the Boston University Center on Emerging Infectious Diseases. From 2024 through spring 2025, the CDC had tracked 70 H5N1 cases, of any type, in the U.S., and most have been mild. The one person who died was over 65 and had underlying health conditions—but he also had the newer D1.1 strain, as did a teen in Canada who became severely ill. Although it's not fully clear what D1.1 means for people, it could be bad news, speculates Friedrich. "I have this gut feeling, and colleagues of mine do too, that something about the D1.1 genotype may be more permissive for mutations that adapt the virus to humans," he says. For the general public, the main advice experts offer is to not consume raw milk or undercooked poultry products. Though no human infections from raw milk or undercooked food have been reported to the CDC as of spring 2025, the virus may have been transmitted via raw poultry products in a small number of cases in Southeast Asia, and it has infected cats that drank unpasteurized milk. Pasteurization kills the virus; so does cooking of eggs, chicken and beef. The U.S. does have some protections ready, including a stockpile of personal protective equipment, antiviral medication—Tamiflu reportedly works on this virus—and the ingredients for making human vaccines. Those ingredients include virus bits, as well as chemicals that help stimulate the immune system. These are stored in bulk, and could be assembled into ready-to-use vaccine doses within weeks to months. Although those vaccine materials were designed using versions of H5N1 flu from the early 2000s, a recent study suggests that they create an antibody response to the newer 2.3.4.4b versions that have spread globally since 2020, and include both B3.13 and the newly circulating D1.1. Scientists are also working on updated vaccines that would more closely match the virus circulating now. Social factors could also influence the detection of, and response to, a potential pandemic. Many farm workers are undocumented immigrants, making many reluctant to be screened or seek medical attention. "The population we should be surveilling the most is the population we're probably not surveilling at a robust enough level," says Pitesky. And Friedrich notes the great paradox of the Covid-19 pandemic: It spawned a society that's less prepared to manage the next outbreak. "The pandemic eroded public trust in science," he says. "There has been a backlash against the power of public health agencies to do what they need to do to control an outbreak." In early 2025, publication of a CDC report on H5N1 flu spreading from cattle to people was delayed. USDA personnel working on bird flu response were laid off; the department later struggled to reinstate them. And $590 million in funding for an RNA-based vaccine (of the kind that proved successful during the Covid pandemic) was put under review. The changes continue, with the resignation of a top vaccine official within the US Food and Drug Administration in March and movements starting in April to lay off thousands of federal health workers. Regardless of whether H5N1 jumps from person to person sooner, later or never, it's raging in wild animals. In the U.S., thousands of birds of more than 160 native species, including mallards, sparrows, pigeons and bald eagles, have been infected. So have hundreds of mammals of more than two dozen native species, including raccoons, bears and opossums. Some of these get sick, and some die. Many of these infections are "dead ends," Richards notes: They don't pass the virus on. It's mainly far-flying ducks that have done that. By late 2022, H5N1 had entered South America and was thundering down the continent's Pacific coast. "It then traveled the 6,000-kilometer spine of South America in six months, so that's very fast for a virus that's not assisted by planes," says Wille. It hit the tip of South America and jumped to Antarctica. En route, it killed 40 percent of Peruvian pelicans, at least 24,000 South American sea lions and more than 17,000 southern elephant seal pups. Wild birds have been affected around the world, and even waterbirds, which normally harbor influenza A without symptoms, have suffered. Though a full census is lacking, individual examples are sobering. The population of great skuas, found primarily in Scotland, is down by a reported 75 percent. An outbreak in California condors in 2023 killed 21 animals, in a species with fewer than 1,000 in existence. "An event like that could change the course of a species," says Wille. "Are they going to come back or not?" H5N1 hasn't reached Australia or New Zealand, but Wille thinks it's just a matter of time. For the world, the future of this virus, with its propensity to defy expectations, is up in the air. "I think we're on the precipice of something," says Wille. "What that something is, I'm not sure." This story was produced by Knowable Magazine and reviewed and distributed by Stacker.
Atlantic
07-12-2024
- Atlantic
The Clue That Tracked a Butterfly Across the Atlantic Ocean
This article was originally published by Knowable Magazine. On a warm summer morning in Ieper, Belgium, 66-year-old Sylvain Cuvelier steps into his blooming garden with his 14-year-old granddaughter, hoping to identify and count all the fluttering butterflies. Other days, he helps scientists by netting butterfly samples. Then he records each sighting's location using GPS, logs them in his Excel database, and sometimes sends the samples to his academic colleagues, who will analyze pollen grains clinging to the insects' bodies. Those tiny pollen grains, gathered by citizen scientists like Cuvelier, are helping researchers study a process that until now has been largely inscrutable: the migratory patterns of insects as they move around the globe over the course of multiple generations. Using pollen, scientists have been able to identify where individual butterflies began their journeys, and even infer the events that likely triggered their migration. The knowledge may help conservationists better understand some of the effects of climate change—not only on the insects themselves, but on their migrations and the ecosystems they inhabit. A lot of insects spend their whole life in one place. Many others migrate, like many birds do, to avoid harsh weather, to find food, or to breed. Some estimates suggest that trillions of insects migrate across the globe each year, yet scientists know little about where they go or how they get there. Tracking insect migration is not as straightforward as tracking birds or mammals. With birds, 'you can attach a ring to the leg or use radio tracking, and it's easy to prove that they move from point A to B,' says Tomasz Suchan, a molecular ecologist at the Polish Academy of Sciences, in Krakow. But most insects are too small for these techniques to be successful. In North America, researchers have had some success tracking monarch butterflies, known for their remarkable migration from southern Canada and the northern United States to central Mexico. In the early 1990s, the Monarch Watch citizen-science initiative began tagging butterflies around the Rocky Mountains. Over 2 million monarchs have been tagged, with more than 19,000 recoveries reported in Mexico, where monarchs congregate to roost for the winter. This has helped biologists track their migration routes. Butterflies without such well-defined aggregations are more difficult to track, however. For example, painted lady butterflies often appear in Europe in the fall, sometimes in great abundance. 'Then they disappear, and we don't really know where they go,' says Gerard Talavera, an entomologist at the Institut Botànic de Barcelona. Some years back, Talavera and his team realized they might be able to track the butterflies indirectly, by studying the pollen that accumulates on their bodies. Every time a butterfly visits a flower for a sip of nectar, it also picks up grains of pollen. If the researchers could identify plants from their pollen, confirm where and when the plants were blooming, and keep tracing them as the butterflies reached different geographic regions, perhaps they could trace the butterflies' overall journey. 'The method is like we put a GPS on them,' Talavera says. 'Because we cannot do that, this is the closest we can go.' The scientists were able to test the idea in 2019, when painted ladies experienced one of their sporadic population booms. In March of that year, as swarms of the butterflies appeared in the Middle East and the Mediterranean, the citizen scientists netted butterfly samples, then preserved them in an alcohol mixture and shipped them to Talavera's lab. There, researchers isolated the pollen grains attached to the butterflies' bodies and sequenced a particular stretch of the pollen DNA that offers a unique signature for each plant species, a process known as metabarcoding. All the while, citizen scientists kept netting butterfly samples as the population surge gradually spread through Eastern, Northern, and Western Europe over the following months, reaching southern Morocco in early November. Analyzing pollen collected from 264 butterflies from 10 different countries in seven months, the researchers identified 398 different plants they could use to track the butterflies' movements backward through the year. From this, they found that swarms of butterflies observed in Russia, Scandinavia, and the Baltic countries were likely the offspring of butterflies originating from the surge in Arabia and the Middle East. This appears to have spread to Eastern Europe, then Scandinavia, and then to Western Europe, resulting in a noticeable population boom in the United Kingdom, France, and Spain. From there, the butterflies may have migrated to southern Morocco, likely continuing on to tropical Africa to complete their annual cycle. The pollen record even suggested a reason painted ladies suddenly became so abundant in 2019. Butterflies collected from the eastern Mediterranean, right at the beginning of the population spike, were carrying pollen from plant species found primarily in semi-arid shrublands, grasslands, and salt marshes of northern Arabia and the Middle East. Examining satellite images, the researchers noticed that from December 2018 to April 2019, those plants experienced big boosts in growth following a period of unusually heavy rainfall. That burst of growth, the researchers speculate, may have provided ideal conditions for the butterflies to feed and breed, kicking off the population explosion and leaving a ripple effect felt by many generations. Talavera and his team have used pollen signatures to track other butterfly movements as well. In 2013, for example, painted lady butterflies had been found resting on the northeast coast of South America, in French Guiana. Painted ladies don't normally live in South America, and it was a mystery where they had come from. A decade later, Talavera's team sampled pollen from the still-preserved butterfly bodies and found that Guiera senegalensis, a plant found only in sub-Saharan Africa, was by far the most common type of pollen attached to these butterflies. By analyzing coastal surveys, wind patterns, pollen, and environmental conditions, they confirmed that the butterflies probably crossed the Atlantic in up to eight days' worth of continuous flight from Africa. This finding marked the first verified instance of an insect crossing the Atlantic. 'The use of pollen metabarcoding to track where each generation of butterflies comes from and how they progress through the cycle is super novel,' says Christine Merlin, a biologist at Texas A&M University and a co-author of an article on the neurobiology of butterfly migration in the Annual Review of Entomology. Because it identifies individual plant species, she notes, this method promises greater precision than the standard method, isotope-signature analysis, which tracks regional variations in the insects' chemical makeup. Though painted ladies serve as a model system for understanding insect migration, researchers say they are confident that this method could be suited for tracking other migrating pollinators that actively visit flowers to collect nectar, including other butterflies, syrphid flies, wasps, beetles, and moths. Tracking migration routes of insects could be of growing importance in the face of changing climate, because such insects can carry fungal diseases in addition to pollen. In fact, Suchan detected many species of fungi in some butterflies. Approximately 1,000 fungi are known to affect insects and more than 19,000 can affect crops. Thus, migrating insects could potentially spread these fungal diseases across continents, posing risks to ecosystems and economies. Talavera, Suchan, and their colleagues hope that using pollen signatures to map changing migration patterns could help predict where fungal-disease outbreaks might occur. Cuvelier, meanwhile, hopes to continue counting butterflies with his granddaughter. Ecologists will continue to need more 'big data' to understand large-scale phenomena, he says. Without citizen scientists, he says, 'it is impossible for researchers to gather such databases.' Besides, he adds, young people have more to learn from citizen science than just how to catch a butterfly. 'They learn about nature,' he says, 'and this fosters curiosity in the world.'
