Short Wave - The magic — and science — of synchronous fireflies

Episode Date: May 25, 2026

Every year for two weeks between mid-May and mid-June, Congaree National Park 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. Read Pien's full story here.Want more of the science behind wildlife wonders? Email us at [e-mail] 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.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 for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Hey, Short Waver is Regina Barber here. And a few weeks ago, I went on a wild nighttime ride. We're in this, like, cart that this lady is biking us around with a dog. And we're looking for bugs. Friend of the show and wonderful beloved reporter, Ping Wong, was there. We are loaded up here in the cargo wagon. 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. It was a tight fit. It was. I felt terrible pink. Because you had organized this trip to see something very specific and very special. It's true, Gina. We were out on a bike trail at 9 p.m. on a weekday for a reason.

And even though there were cars zooming past us, planes flying overhead, the conditions were actually totally perfect. They were magical. Like, I'm looking out into the marsh and I'm seeing all these, like, the darkness and bushes. And then you just see like pops of light. It feels like a fairy tale. I keep on saying Disneyland, but it really... Yeah, it was the magic time of summer in and around Washington, D.C., when you can see fireflies. Hundreds of them.

Thousands of them blinking their belly lanterns on and off so long as you know where to look. 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. And we'll talk about why some are endangered and how you can help. You're listening to Shortwave, the science podcast from NPR. 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. 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. So why is water so important to fireflies? 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 hatches larva. 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 pupil stage. and it can last a couple 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.

I spoke with Lynn Fierce and 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. A lot of these species, many of them, they flash 20 minutes a night, And that's it. And they only live two weeks. So if you're not standing in the right place at the right time, look in the right direction, you'll miss them. 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? 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. Okay, Ping. So those weren't the only fireflies you saw this summer, though, right? I know you're dying to tell me more. Yes, absolutely.

So you're right. Earlier in the season, I actually went on a trip looking for fireflies down at Congre 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 our. across a large expanse of nature, so they're blinking all at the same time. Oh, that sounds really, really cool. Can you only see them in South Carolina? 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. Congrey, where I went, has one kind, and the Great Smoky Mountains in East Tennessee has another. Lynn Fireson Fess has seen both kinds. What the Great Smoky Mountains National Park has is Fetanis, Carolinas, that is completely different from what is here at Congri is Futurus Frontalus. Different genus, different everything. She says that even the way that they flash is different. Carolinas do

this explosion of flashes for three seconds and then the whole forest goes dark for six seconds. The Congri synchrony is constant like that. Weird. Yeah, and Regina, that's exactly what I saw.

When I 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. 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. It makes me think of those like drone fireworks. I mean, it did look like LED lights a little bit. Yeah. How are they coordinating, though? Like, how are they doing this? Well, that's still kind of a mystery, something researchers are trying to figure out. So when I was down at Congaree, I met up with Orit Paley. She's a computer scientist and biophysicist at the University of Colorado in Boulder.

And Orete had come to the Congaree with some folks in her lab to study how this fly synchrony works. She says that there does seem to be this evolutionary advantage to having a whole form of fireflies blinking at the same time. It boosts their signal, makes them more visible to their mates down on the ground. And we're trying to understand how they manage to do it. 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. Arate 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 sink with LED lights. Wow. 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. Arrete 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. This is, like, fascinating. but it also sounds like really magical to witness. It was. It was completely magical for me. Beautiful. But as Lynn says, the fireflies aren't actually doing it for our benefit. I'm sure. 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. If they don't get those eggs in the ground for the next generation, they're done. 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 culling feral hogs who root around in the dirt and destroy firefly eggs. Wow. Okay. So these are well-known, well-studied fireflies, protected.

by the park, are there firefight populations that aren't so lucky? Yes, most of them, I would say. So for some context, I called up Sarah Lewis, who's a professor, Emerita, at Tafts University, and she 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 okay. I was telling her about this droopy, swoopy firefly I've been seeing in D.C. And she was like, Oh, yeah, that's the big dipper firefly. 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 find under streetlights, no problem. Now, Sarah says that out of the 170 or so firefly species that are in the U.S., about one third fall into this category, well-studied, doing fine. On the other hand, there's about 10% of U.S. fireflies that are not doing so well, that are some degree of threatened with extinction. Okay, so 30% are fine, 10% or not. What about this other 60%? About. 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.

Wow. Okay. So you can just go collect data for this project? 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. Okay. And then you go out at night to look for them. So for the fireflies that aren't doing so well, do researchers know why? 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. They use bioluminescent signals against a background of what used to be dark. 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 meets. Okay, so this sounds like big environmental issues. Is there anything I can, 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. And I want to keep them going. 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 switch off the outdoor lights, use motion detectors so they're not constantly on anything really to help these burgers grow to adults and find their mates so that their cycles can continue on. I'm so excited. I'm doing everything right.

Thank you so much for this reporting ping. Thanks for coming with. It's been so much fun. This episode was produced by Rachel Carlson. It was edited by Burley McCoy and fact-checked by Ping. Quasi Lee was the audio engineer. Special thanks to our local tour guides, Cameron Taylor, Josephine Liu, and Judd Isbell. With friends of the Mount Vernon Trail.

I'm Regina Barber. Thank you for listening to Shortwave from NPR.