The magic — and science — of synchronous fireflies

Every year for two weeks between mid-May and mid-June, Congaree National Park https://www.nps.gov/cong/fireflies.htm in South Carolina is home to a fairy-tale-like display of flashing lights. These rhythmic performances happen all because of thousands of fireflies, flashing their belly lanterns at exactly the same time. According to the National Park Service, there are just three species of these synchronous fireflies in North America, making the experience all the more magical for the lucky visitors who get the chance to see them. (encore) This story was originally reported for NPR by science correspondent Pien Huang https://www.npr.org/people/729920828/pien-huang. Read Pien's full story here https://www.npr.org/2024/05/24/g-s1-935/synchronous-fireflies-congaree-endangered. Want more of the science behind wildlife wonders? Email us at [email protected] mailto:[email protected]. Listen to every episode of Short Wave sponsor-free and support our work at NPR by signing up for Short Wave+ at plus.npr.org/shortwave http://plus.npr.org/shortwave. Today's episode was produced by Rachel Carlson. It was edited by Berly McCoy. Pien checked the facts. Kwesi Lee was the audio engineer. See pcm.adswizz.com https://pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences. NPR Privacy Policy https://www.npr.org/about-npr/179878450/privacy-policy

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• 0:20Regina Barber?

  Hey, Short Wavers. Regina Barber here. And a few weeks ago, I went on a wild nighttime ride.

• 0:26Speaker 02

  We're in this, like, cart that this lady is biking us around with a dog. And we're looking for bugs.

• 0:34Regina Barber?

  Friend of the show and wonderful, beloved reporter Ping Wong was there.

• 0:39Speaker 03

  We are loaded up here in the cargo wagon.

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  Cargo bike. Cargo bike. And we are very tightly pushed in. And Ping is a patient, patient woman. And she has a dog on one side of her and me smushing her on the other side.

• 0:57Speaker 03

  It was a tight fit.

• 0:59Speaker 02

  It was. I felt terrible, Ping, because you had organized this trip to see something very specific and very special.

• 1:06Speaker 03

  It's true, Gina. We were out on a bike trail at 9:00 PM on a weekday for a reason. And even though there were cars zooming past us, planes flying overhead, the conditions were actually totally perfect.

• 1:21Regina Barber?

  They were magical.

• 1:21Speaker 02

  Like, I'm looking out into the marsh and I'm seeing all these, like, the darkness and bushes. But and then you just see, like, pops of light. It feels like a fairy tale. I keep on saying Disneyland, but it really...

• 1:35Regina Barber?

  Yeah, it was the magic time of summer in and around Washington DC when you can see fireflies.

• 1:40Speaker 03

  Hundreds of them, thousands of them, blinking their belly lanterns on and off, so long as you know where to look.

• 1:48Regina Barber?

  Today on the show, the brief and wondrous adult lives of fireflies. We'll take you on a trip down the East Coast to see some special species.

• 1:57Speaker 03

  And we'll talk about why some are endangered and how you can help.

• 2:01Regina Barber?

  You're listening to Short Wave, the science podcast from NPR.

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• 3:29Regina Barber?

  Okay, so a few weeks ago, on a hot, humid night, we saw an incredible firefly show, AKA lightning bug show. And seriously, Ping, it was this random little patch of dense forest, like, sandwiched in between the airport and the parkway.

• 3:44Speaker 03

  Right. That little protected marsh between the bike path and the Potomac River was actually the perfect habitat for some fireflies. So there's a lot of different species, but what they all seem to have in common is a love for warm, humid environments, maybe some tall grass, and definitely some standing water. Seriously, one of the big enemies of fireflies is drought.

• 4:05Regina Barber?

  So why is water so important to fireflies?

• 4:08Speaker 03

  Well, I say it's the water and the dirt. And both of these are important to their life cycles. So fireflies are beetles, and so they've got that four-part life cycle. They start as eggs, then they hatch as larvae. And the larval stage is actually where they spend most of their lives. They can spend up to one to two years crawling around underground, eating other invertebrates. And then they burrow down generally into the ground. This is called their pupal stage, and it can last a couple of weeks. And this is where they really transform themselves. Then they emerge as full adults, and that's when people like us, walking around at night, can see them flying around and flashing in fields and trees.

• 4:49Speaker 03

  I spoke with Lynn Frierson Faust. She's author of "A Firefly Field Guide to the Eastern and Central U.S. and Canada." And she says that adult stage is relatively brief.

• 5:00Speaker 07

  A lot of these species, many of them, they flash 20 minutes a night. And that's it.

• 5:07Speaker 07

  And they only live two weeks. So if you're not standing in the right place at the right time, looking the right direction, you'll miss some.

• 5:15Regina Barber?

  Yeah, I mean, it was a brilliant light show that we saw a few weeks ago. And we caught like the tail end of this year's peak of fireflies in northern Virginia, right?

• 5:24Speaker 03

  Right. And right now, it doesn't look like that anymore. And when the fireflies peak depends a lot on how hot and humid it's been in the weeks and months just before it.

• 5:33Regina Barber?

  Okay, Ping, so those weren't the only fireflies you saw this summer, though, right? I know you're dying to tell me more.

• 5:39Speaker 03

  Yes, absolutely. So you're right. Earlier in the season, I actually went on a trip looking for fireflies down at Congee National Park, which is near Columbia, South Carolina. Since further south, where it's hotter and humid, the fireflies come out earlier. And I went to see a specific behavioral phenomenon, synchronous fireflies. These are hundreds, thousands of fireflies that are all coordinating across a large expanse of nature, so they're blinking all at the same time.

• 6:09Regina Barber?

  Oh, that sounds really, really cool. Can you only see them in South Carolina?

• 6:12Speaker 03

  Okay, well, they're rare, but they're not that rare. So there's just a few species of synchronous fireflies in the U.S. Congee, where I went, has one kind. And the Great Smoky Mountains in east Tennessee has another. Lynn Frierson Faust has seen both kinds.

• 6:28Speaker 07

  What the Great Smoky Mountains National Park has is Phytinus carolinus. That is completely different from what is here at Congee, is Phyturus frontalis. Different genus, different everything.

• 6:40Speaker 03

  She says that even the way that they flash is different.

• 6:43Speaker 07

  Carolinas do this explosion of flashes for three seconds, and then the whole forest goes dark for six seconds. The Congee synchrony is constant, like that.

• 6:56Regina Barber?

  Weird.

• 6:57Speaker 03

  Yeah. And Regina, that's exactly what I saw. When it got dark, like really dark in the forest, I started seeing these little flashes in the trees. You know, at first, it was like a couple of them blinking randomly. And then, as more and more of them joined in, I started to see this pattern emerging, like a rolling wave of lights.

• 7:17Speaker 03

  And then, at some point, they synced up perfectly, at least to my human eye, and they were all flashing at once. And that was a pattern that they kept up for a little while before it just sort of went back through the cycle all over again.

• 7:31Regina Barber?

  It makes me think of those drone fireworks.

• 7:34Speaker 03

  I mean, it did look like LED lights a little bit.

• 7:37Regina Barber?

  Yeah. How were they coordinating, though? Like, how are they doing this?

• 7:41Speaker 03

  Well, that's still kind of a mystery, something researchers are trying to figure out. So when I was down at Congress, I met up with Arit Paleig. She's a computer scientist and biophysicist at the University of Colorado in Boulder. And Arit had come to the Congress with some folks in her lab to study how this firefly synchrony works. She says that there does seem to be this evolutionary advantage to having a whole swarm of fireflies blinking at the same time. It boosts their signal, makes them more visible to their mates down on the ground.

• 8:11Regina Barber?

  And we're trying to understand how they manage to do it. You know, they're very small creatures. They have limited visual perception. And they certainly cannot communicate directly with all the other fireflies in the swarm. But somehow, just by communicating with a small group that are near to them, they're able to create global synchronization, which is just a feat of animal behavior, I think.

• 8:37Speaker 03

  Arit says that visual cues are a big part of it. And she says they know this because they can actually get fireflies to flash and sync with LED lights.

• 8:45Regina Barber?

  Wow.

• 8:45Speaker 03

  When the fireflies get closer, they also communicate with chemicals, pheromones, too. But what's really cool about this is that there doesn't seem to be one leader in the pack. Arit has taken videos from within and around these flashing swarms. She's slowed them down. And she says that it seems like it can really originate from all kinds of different places in the pack.

• 9:06Regina Barber?

  This is fascinating, but it also sounds like really magical to witness.

• 9:11Speaker 03

  It was. It was completely magical for me, beautiful. But as Lynn says, the fireflies aren't actually doing it for our benefit.

• 9:20Regina Barber?

  I'm sure.

• 9:21Speaker 07

  They have just a few minutes each night to find a mate. And sometimes, it's as many as 100 males to one female. You know, we think it's beautiful, and we love looking at it. But for them, it's life and death.

• 9:38Speaker 07

  If they don't get those eggs in the ground for the next generation, they're done.

• 9:45Speaker 03

  Now, unlike some other firefly species, the synchronous fireflies at Congaree are actually doing pretty well. The park started limiting the number of visitors after they realized that overcrowding was disturbing the fireflies. And they've also been calling feral hogs, who root around in the dirt and destroy firefly eggs.

• 10:03Regina Barber?

  Wow, OK. So these are well-known, well-studied fireflies, protected by the park. Are there firefly populations that aren't so lucky?

• 10:12Speaker 03

  Yes, most of them, I would say. So for some context, I called up Sarah Lewis, who's a professor emerita at Tufts University. And she's studied fireflies for many years. And now she's actually focused on conserving them. Now, Sarah Lewis says that all the fireflies I saw this summer are the fireflies that are doing OK. I was telling her about this droopy, swoopy firefly I've been seeing in DC. And she was like, oh, yeah, that's the Big Dipper firefly.

• 10:38Speaker 02

  It's an urban firefly. And it doesn't really care about light pollution. We think one of the reasons for that is because it flies just at sunset, where it's really actually still quite light out. And so it does fine under streetlights, no problem.

• 10:55Speaker 03

  Now, Sarah says that out of the 170 or so firefly species that are in the US, about one-third fall into this category: well-studied, doing fine.

• 11:05Speaker 02

  On the other hand, there's about 10% of US fireflies that are not doing so well, that are some degree of threatened with extinction.

• 11:17Regina Barber?

  OK, so 30% are fine, 10% are not. What about this other 60% about?

• 11:25Speaker 03

  Yes, math. Well, Sarah says there are just huge gaps in our knowledge on these other fireflies because the research is really time-intensive and it's not well-funded. Now, there is a movement to get community scientists involved. Sarah and some others have launched a project called Firefly Atlas. It's enlisting volunteers to go out and survey for 13 specific firefly species that are considered data deficient.

• 11:50Regina Barber?

  Wow, OK. So you can just go collect data for this project?

• 11:55Speaker 03

  Well, you do have to register. And then you also have to watch this like hour-long training video that tells you what data to collect.

• 12:02Regina Barber?

  OK.

• 12:02Speaker 03

  And then you go out at night to look for them.

• 12:04Regina Barber?

  So for the fireflies that aren't doing so well, do researchers know why?

• 12:09Speaker 03

  So Sarah says that there's two things in particular: habitat destruction and light pollution. And that habitat destruction can come from human development or natural disasters and droughts. And it can hit some fireflies particularly badly because there are certain species that really need the specific conditions in like a cypress swamp or a freshwater wetland to survive. And then there's light pollution.

• 12:33Speaker 02

  They use bioluminescent signals against a background of what used to be dark.

• 12:41Speaker 02

  And as we light up more and more of the night, it makes it very hard for these flashing fireflies to be able to see each other and to be able to find mates.

• 12:51Regina Barber?

  OK, so this sounds like big environmental issues. Is there anything I could, like me, I can do to help, aside from like helping the scientists collect data? Like, I love these fireflies, especially the ones we saw, like, and I want to keep them going.

• 13:04Speaker 03

  Yeah, so Regina, if you're in a place where fireflies can live and you have a backyard or a front strip, or you're responsible for a patch of nature somewhere, you can help to make it a good firefly habitat. Sarah says that this means having shrubs, native plants, and really critically not spraying your lawn with broad-spectrum insecticides, which can kill fireflies, too. You know, another thing you can do to help is to leave some leaf litter around, make it a place where firefly larvae and the things that they eat can thrive. And you can also, of course, cut down on light pollution in your home or in your environment. So you can, you know, switch off the outdoor lights, use motion detectors so they're not constantly on anything, really, to help these beggars grow to adults and find their

• 13:48Speaker 03

  mates so that their cycles can continue on.

• 13:51Regina Barber?

  I'm so excited. I'm doing everything right.

• 13:55Regina Barber?

  Thank you so much for this reporting, Ping.

• 13:57Speaker 03

  Thanks for coming with. It's been so much fun.

• 14:03Regina Barber?

  This episode was produced by Rachel Carlson. It was edited by Burley McCoy and fact-checked by Ping. Kwasi Lee was the audio engineer. Special thanks to our local tour guides Cameron Taylor, Josephine Lu, and Judd Isbell, with Friends of the Mount Vernon Trail. I'm Regina Barber. Thank you for listening to Short Wave from NPR.

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