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Thousands of fireflies emerge in South Carolina to put on a mind-blowing light show

ARI SHAPIRO, HOST:

For a few weeks each spring, thousands of fireflies emerge at the Congaree National Park to blink together. It's a natural wonder that's ephemeral and rare in the U.S. NPR's Pien Huang went to Columbia, S.C., to check them out.

(CROSSTALK)

PIEN HUANG, BYLINE: It's twilight at the Congaree National Park. A wooden boardwalk weaves through cypress trees and towering loblolly pines. A viewing platform holds the lucky few that won the lottery, the park lottery, to come see thousands of fireflies blinking in synchrony for a few short weeks this spring. Hrudaya Reddy flew in from San Francisco.

HRUDAYA REDDY: There have been very few moments where my mind has been blown, so I'm hoping the feeling will be the same.

HUANG: She's here with her husband, Shiva Vanamala, who thinks he saw fireflies as a child growing up in southwest India.

SHIVA VANAMALA: I remember watching fireflies as a kid, but now I'm not sure if that was a dream or if it really happened.

HUANG: There are more than 2,000 different kinds of fireflies around the world, over 170 in North America and just three in the U.S. that coordinate their belly lanterns to flash at exactly the same time. That's according to the National Park Service. These synchronous fireflies became known to scientists in the 1990s thanks to Lynn Frierson Faust.

LYNN FRIERSON FAUST: As a child growing up in east Tennessee, we just - we call them lightning bugs, and they're just part of summer. You don't even notice them hardly.

HUANG: A few decades back, Faust read an article in a science magazine which said there are no synchronous fireflies in the Western Hemisphere.

FAUST: And I thought, ours are synchronous. So I thought, well, who do I tell this to?

HUANG: She wrote a letter to researchers, who came to Tennessee and studied those fireflies for the next 20 years. Faust is now a leading expert herself. She's written a firefly field guide and consults with the Park Service and researchers. She drove six hours from the Great Smoky Mountains in Tennessee to get to the Congaree.

FAUST: What the Great Smoky Mountains National Park has is Photinus carolinus. That is completely different from what is here at Congaree, is Photuris frontalis. Different genus, different everything.

HUANG: Faust says they even flash in different patterns.

FAUST: Carolinus do this explosion of flashes for three seconds, and then the whole forest goes dark for six seconds. And the Congaree synchrony is constant, (clapping), like that.

HUANG: Faust is here with researchers like Orit Peleg from the University of Colorado in Boulder. Peleg is a biophysicist who's looking into how the fireflies communicate.

ORIT PELEG: They're basically saying, hi, I'm a Photuris frontalis firefly and I would like to mate. I'm a male. And then they're looking for a response from a female.

HUANG: But one firefly blinking on his own isn't very visible. When a group of them blink together, they're much more likely to be seen. Peleg says the fireflies are communicating visually to a small group around them. At first it seems random, and then it's a wave that spreads.

PELEG: In dusk, so as the sun set, you'll start seeing, like, little flickers here and there.

NANCY CANTERBURY: Oh, I just saw one. Yeah. Yeah - see? - right straight ahead.

PELEG: But very quickly before you notice it, you'll see more and more fireflies coming out, you know, probably like a hundred flashes within your field of view.

CANTERBURY: Oh, yeah. I'm seeing more and more now.

HUANG: The daylight is fading at the Congaree. Nancy Canterbury from Cary, N.C., sees a cluster through the trees. The fireflies give off a cool white light.

CANTERBURY: They're faster than I remember, too.

HUANG: These Photuris fireflies are also called snappies because they blink quickly, about twice every second. Nearby on the boardwalk, Reddy and Vanamala, who had come from California hoping to blow their minds, say it's actually beyond their expectations.

REDDY: Like, I was just trying to follow a few for, like, a few seconds. It's like some magic is happening. He's right here, there, then he's there, then he's there.

VANAMALA: Shooting stars on the ground. It's pretty incredible.

HUANG: These swarms of fireflies can flash in synchrony for hours into the night. From a bench on the viewing platform, Clinton Wessinger sees just a sliver.

CLINTON WESSINGER: I really think it looks like when you're coming down out of the sky, like your plane has landed and you can see the runway, like, the lights flashing as you're, like, being guided in, except like a thousand of them.

HUANG: But would more fireflies be flashing more brightly if they weren't surrounded by people walking wooded trails, waving red flashlights and talking loudly?

WESSINGER: That's what I'm wondering. Like, if we weren't here, would they be going crazy, you know?

HUANG: The park says people do disturb the fireflies. That's why the park limits the number of visitors and kicks them out at 10 p.m. That gives the fireflies some peace and some time to lay eggs in the soil, so that in the future there will be more mind-blowing firefly light shows to come.

Pien Huang, NPR News.

(SOUNDBITE OF OWL CITY SONG, "FIREFLIES") Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Pien Huang is a health reporter on the Science desk. She was NPR's first Reflect America Fellow, working with shows, desks and podcasts to bring more diverse voices to air and online.