Dragonflies Make Epic Migrations, But Climate Change Could Foil Their Itineraries
By Jason Bittel
It's that time of year again: Right now, monarch butterflies are taking wing in the mountains of northwestern Mexico and starting to flap their way across the United States.
The great monarch migration always makes headlines, in part because climate change, along with our pesticides and agricultural monocultures, threatens to erase the natural spectacle, but also because this natural phenomenon is simply amazing. The trip of nearly 5,000 miles is an unlikely one for an insect, but these butterflies don't have a monopoly on the massive, multigenerational migration game.
It's time to give some love to the epic feats of dragonflies.
According to a study published by the Royal Society last fall, common green darners, which are found from Cuba to Canada, make a long, complex journey that takes three generations and spans a distance of more than 1,500 miles. Scientists are still trying to figure out exactly how they do it, but temperature seems to play a key role in telling the animals when to move. Unfortunately, this means climate change could well wreck the whole event even before we fully understand it. Worse, it would leave much of eastern North America without an important member of its food web.
The news that dragonflies migrate probably won't shock people who study insects, says the study's senior author, Colin Studds, a wildlife ecologist at the University of Maryland. "We've had an inkling of how many insects migrate," he said. "There are moths, there are beetles, and there are probably about 20 species of dragonflies that we have expected of migration. But we don't know much about it other than that it's a phenomenon."
One of the reasons why insect migration remains so much of a mystery is that bugs are tough to track. They're tiny, they die all the time, and they're quick as heck — especially dragonflies. "Unlike monarchs, common green darners are fast fliers," said MaLisa Spring, state coordinator for the Ohio Dragonfly Survey at the Museum of Biological Diversity just north of Columbus. "This makes them hard to catch and potentially add identification tags or stickers, and even harder to photograph. Most photo observations are a blur of blue and green, so a tiny sticker doesn't work so well."
This is why Studds and his coauthors decided to study where the dragonflies had been, rather than where the critters were heading. To do this, they took tissue samples from the wings of more than 850 green darners, some collected from the wild and others from museum specimens going back 140 years. A molecular analysis of the wings allowed the scientists to identify hydrogen isotopes that revealed the latitudes at which the dragonflies were born. (These isotopes vary at reliable rates as one moves north or south, so determining which ones are present and in what quantities can drop a pin of origin within about 100 to 200 miles.)
The team also made use of 21 years' worth of citizen science data to understand when and under what conditions dragonflies appear across their vast range. With all of these pieces put together, common green darner migration patterns are no longer so much of a blue-green blur.
Tina Vance / Flickr
In February the dragonflies appear only in warm latitudes, which is reflected in data showing dragonfly emergences at this time in Florida, Louisiana and Texas, as well as Puerto Rico, Cuba and southern Mexico. But come March, this first generation has already winged it up to the American Northeast, the Great Lakes region and southern Canada. And then those well-traveled dragonflies mate, lay eggs and die.
In May and June, the second generation hatches onto the scene. Some live their whole lives locally, but others — driven by what, we do not know — point their beautiful compound eyes south. Between September and November, these snowbirds don floral shirts and sunglasses and can be found flitting around the southern U.S. and Caribbean. Like the first generation, these dragonflies mate, lay eggs and die.
This leaves us with the third generation in the cycle, which are the population's homebodies. Because winter hits the south soon after they hatch, and they definitely don't want to head north to even colder climes, these lucky darners live out their life span locally. And then they ... mate, lay eggs and die like the rest. Their offspring then hatch around February, transform from larvae to adults, and head up north, starting the cycle anew.
The great dragonfly migration has likely been taking place for many millennia. Each generation has a job to do and an itinerary to follow, and every step is tied to a specific temperature range.
"So one of the things that we figured out from the citizen science data of over 20 years across the whole eastern United States is that the dragonflies don't begin migrating until it gets to about 9.5 degrees Celsius, or just shy of 50 degrees Fahrenheit," said Studds. "They kind of wait for it to go up to that point and they follow that temperature north."
Enter climate change. Temperature patterns are shifting all over the U.S. (indeed, the whole planet), and research on monarchs is already showing that such fluctuations may affect how the butterflies inoculate themselves against parasites. Could there be similar consequences for other migratory insects?
"If we are moving into a period where winter temperatures are warming and spring temperatures are getting warmer through time, then that will probably affect the entire timing and pace of dragonfly migration," said Studds. "It will affect how far north they go and how quickly they develop."
In some areas, warmer temperatures year-round may mean dragonflies won't even need to migrate at all. This isn't necessarily bad for the darners, mind you. But because dragonflies are important predators of mosquitoes, aphids, and other insects, as well as nutritious food for ducks, toads, newts, fish and even carnivorous plants like sundew, losing a seasonal influx of these creatures could ripple out through North America's ecosystems. (Plus, dragonflies are beautiful, and people up north will miss them.)
The truth is, scientists still know very little about how these seasonal shake-ups will affect wildlife, and common green darners and monarch butterflies are just two species among many that are facing big changes. But given that insects are experiencing dramatic declines worldwide, we need to unpack as many of these little mysteries as we can now — instead of trying to piece the puzzle back together after it's too late.
Reposted with permission from our media associate onEarth.
By Karen L. Smith-Janssen
Colette Pichon Battle gave a December 2019 TEDWomen Talk on the stark realities of climate change displacement, and people took notice. The video racked up a million views in about two weeks. The attorney, founder, and executive director of the Gulf Coast Center for Law & Policy (GCCLP) advocates for climate justice in communities of color. Confronted with evidence showing how her own South Louisiana coastal home of Bayou Liberty will be lost to flooding in coming years, the 2019 Obama Fellow dedicates herself to helping others still reeling from the impacts of Katrina face the heavy toll that climate change has taken—and will take—on their lives and homelands. Her work focuses on strengthening multiracial coalitions, advocating for federal, state, and local disaster mitigation measures, and redirecting resources toward Black communities across the Gulf South.
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"These are not just wildfires, they are climate fires," Jay Inslee, Governor of Washington State, said as he stood amid the charred remains of the town of Malden west of Seattle earlier this month. "This is not an act of God," he added. "This has happened because we have changed the climate of the state of Washington in dramatic ways."
'These Aren't Wildfires'<p>Sam Ricketts, who led climate policy and strategy for Governor Jay Inslee's 2020 presidential campaign, tweeted on September 11 that "These aren't wildfires. These are #climatefires, driven by fossil fuel pollution."</p><p>"The rate and the strength and the devastation wrought by these disasters are fueled by climate change," Ricketts told DW of fires that have burnt well over 5 million acres across California, Oregon, Washington State, and into neighboring Idaho. </p><p>In a two-day period in early September, Ricketts notes that more of Washington State burned than in almost any entire fire season until now, apart from 2015. </p><p>California, meanwhile, was a tinderbox after its hottest summer on record, with temperatures in Death Valley reaching nearly 130 degrees Fahrenheit, according to the U.S. National Weather Service. It has been reported as the hottest temperature ever measured on Earth.</p>
<div id="29ad9" class="rm-shortcode" data-rm-shortcode-id="8346fe7350e1371d400097cd48bf45a2"><blockquote class="twitter-tweet twitter-custom-tweet" data-twitter-tweet-id="1306969603180879872" data-partner="rebelmouse"><div style="margin:1em 0">Drought-parched wetlands in South America have been burning for weeks. https://t.co/pjAKdFcKPg #Pantanal https://t.co/ImN2C5vwcp</div> — NASA Earth (@NASA Earth)<a href="https://twitter.com/NASAEarth/statuses/1306969603180879872">1600440810.0</a></blockquote></div><p>As evidenced by Australia's apocalyptic Black Summer of 2019-2020, fires are burning bigger and for longer, with new records set year-on-year. Right now, Brazil's vast and highly biodiverse Pantanal wetlands are suffering from catastrophic fires.</p>
#climatefires Started in Australia<p>Governor Inslee this month invoked the phrase climate fires for arguably the first time in the U.S., according to Ricketts.</p><p>But the term was also used as fires burnt out of control in Australia in late 2019. In the face of a 2000km (more than 1,200 miles) fire front, and government officials and media who <a href="https://www.dw.com/en/trump-climate-change-denial-emissions-environment-germany-fake-heartland-seibt/a-52688933" target="_blank">played down the link to climate change</a>, Greens Party Senator Sarah Hanson-Young and a friend decided that reference to bushfires was inadequate. </p><p>"We both just said, we've got to start calling them climate fires, that's what they are," the Australian Senator told DW.</p><p>Hanson-Young says scientists have been warning for decades that these would be the effects of global heating. "We've been told these kinds of extreme weather events and destruction is what climate change would look like, and it's right here on our doorstep," she said from her home state of South Australia — where by early September fire warnings had already been issued.</p><p>"Calling them climate fires was making it absolutely crystal clear. It is essential that there's no ambiguity," she said </p><p>Having deliberately invoked the term, Hanson-Young soon started to push it on social media via a #climatefires hashtag. </p>
How to Talk About the Urgency of Global Heating<p>The need to use more explicit language when talking about extreme weather events linked to climate change is part of a broader push to express the urgency of global heating. In 2019, activist Greta Thunberg tweeted that the term "climate change" did not reflect the seriousness of the situation. </p><p>"Can we all now please stop saying 'climate change' and instead call it what it is: climate breakdown, climate crisis, climate emergency, ecological breakdown, ecological crisis and ecological emergency?" she wrote. </p><p>"Climate change has for a long time been talked about as something that is a danger in the future," said Hansen-Young. "But the consequences are already here. When people hear the word crisis, they understand that something has to happen, that action has to be taken."</p><p><span></span>Some terms are now used in public policy, with state and national governments, and indeed the EU Parliament, declaring an official climate emergency in the last year. </p>
Words That Reflect the Science<p>But while the West Coast governors all fervently link the fires to an unfolding climate crisis, U.S. President Donald Trump continues to avoid any reference to climate. In a briefing about the fires, he responded to overtures by Wade Crowfoot, California's Natural Resources Secretary, to work with the states on the climate crisis by stating: "It'll start getting cooler. You just watch." Crowfoot replied by saying that scientists disagreed. Trump rejoined with "I don't think science knows, actually." </p><p>It was reminiscent of the anti-science approach to the coronavirus pandemic within the Trump administration, <a href="https://www.dw.com/en/donald-trump-admits-playing-down-coronavirus-risks/a-54874350" target="_blank" rel="noopener noreferrer">at least publicly</a>. Fossil fuel companies are also benefiting from his disavowal of climate science, with the Trump administration having <a href="https://www.dw.com/en/opinion-trumps-paris-climate-accord-exit-isnt-really-a-problem/a-51124958" target="_blank" rel="noopener noreferrer">pulled out of the Paris Agreement</a> and reopened fossil fuel infrastructure like the Keystone XL pipeline. </p><p>But the science community has responded, with Scientific American magazine endorsing Trump's Democratic presidential challenger Joe Biden, the first presidential endorsement in its 175-year history. </p><p>Hanson-Young says the use of explicit language like climate fires has also been important in Australia due to the climate denialism of politicians and the press, especially in publications owned by Rupert Murdoch. As fires burnt out much of Australia's southeast coast, they were commonly blamed on arson — a tactic also recently used in the U.S.</p>
Climate Rhetoric Could Help Decide Election<p>The language of climate has begun to influence the U.S. presidential election campaign, with Democratic nominee Joe Biden labelling President Trump a "climate arsonist."</p><p>Biden is touting a robust climate plan that includes a 2050 zero emissions target and a return to the Paris Agreement. Though lacking the ambition of The New Green Deal, it has been front and center of his policy platform in recent days, at a time when five hurricanes are battering the U.S. Gulf Coast while smoke blanketing the West Coast spreads all the way to the East. </p><p>People are experiencing the climate crisis in a visceral way and almost universally relate to the language of an emergency, says Ricketts. "They know something is wrong."</p>
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