This story was originally published on July 14, 2012.

One of summer’s biggest delights is the arrival of fireflies. To the untrained eye, the luminous blinking of these small insects may look the same. But, in fact, there are at least 2,000 species around the world, and each flashes its own signals.

In northern Pennsylvania, fireflies are putting on a particularly unusual show. They’re blinking in sync. In the last couple years, researchers from around the world have visited the Allegheny National Forest to study the phenomenon and report their findings. On June 25, 2016, from noon to midnight, The Pennsylvania Firefly Festival offers a chance for the rest of us to witness the rare display.

LISTEN: “Pennsylvania Fireflies Put on a Brilliant Show”

But let’s step back to a time before the festival, when just a few people were onto the beetles. That’s when this reporter first visited the Allegheny National Forest to see the show in 2012 with Ken Butler and his wife, Peggy, who own a bed and breakfast near site of the big discovery.

Fireflies that flash in sync had been found across the road. Scientists had thought that synchronous fireflies were only found in pockets of the Great Smoky Mountains and in southeast Asia. But the Butlers started taking guests to see the light show in their neck of the Allegheny National Forest.

“It looks like a lighted Christmas display out there,” Peggy says. “It’s really amazing.”

Ken says the forest really is lovely, dark and deep. He guides us to the location where the synchronous fireflies were first spotted in 2011.

“Should we go up to the famous Camp 11?” he says.

The canopy of spruce, oak and hemlock blocks out most of the moonlight. About a quarter of a mile into the woods, Ken shines his flashlight on a landmark boulder in the national forest campsite.

Then he turns off his light and stands motionless in the dark. At first, a few random male fireflies flash. Then the choreographed blinking happens all around.

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A firefly in full flight. Photo: Terry Priest via Flickr

Clusters of fireflies fly about four feet off the ground and light up the brush with their luminous tails. They flash five or six times together and then stop for about 10 seconds. Then they flash in unison again and the forest returns to darkness while they recharge the biochemicals that allows them to glow.

“Spectacular,” Peggy says. “It’s like a natural fireworks show.”

Peggy claps her hands to demonstrate how the fireflies can start and stay in unison for several hours at a time.

“If you clap your hands once and say, ‘Everyone clap with me,’ but you only clap once, it’s really hard to synchronize with that,” Peggy says. “But if I say, ‘Everybody clap with me,’ and I clap multiple times, by the second or third time I clap, everyone can be in synchrony with me.”

Peggy picked up this insight from naturalist Lynn Faust. Faust came to the Allegheny National Forest earlier this summer with an international team of firefly researchers. They logged lots of late-night hours in the forest observing this synchronous population and studying them at their makeshift lab in the Butlers’ garage. Faust has studied the life cycle of synchronous fireflies in the Smoky Mountains for 20 years. She says the all-male light display is basically a sexual competition.

“I used to get the impression I was watching teenage boys revving their engines, driving down the road,” Faust says.”They’re all about the females, but they’re also competing with themselves.”

LISTEN: “Nature Photographer Talks About the Challenge of Photographing Fireflies”

While the guys show off, females hang out in the grass or the low tree branches. Just like other species of fireflies, the females recognize their male’s specific flash pattern. If they’re interested, they blink back. The males will then drop out of the air like little shooting stars to try to mate.

“They are quite desperate, and you can appreciate their desperation to find that mate and get their life cycle completed to assure the next generation,” Peggy says.

These little insects symbolize something bigger. It seems nature wants to be in sync. Steve Strogatz, at Cornell University, writes about synchronous fireflies as an example of natural organization. He says this drive exists in everything from human cells to planets.

“The fireflies are a paradigm of this larger theme of nature organizing itself, which has been very difficult for scientists to understand,” Strogatz says. “It’s really the subject for the whole 21st century.”

Peggy and Ken Butler both agree that the science behind the synchronous fireflies is fascinating, but they think the fireflies’ light display also signals something else.

“We need to slow down and enjoy nature,” Peggy says. “There’s nothing nicer than pulling up a chair and watching the fireflies.”

Thousands of people go to the Smoky Mountains to watch the synchronous fireflies there. Peggy and Ken hope with the right planning, the Allegheny National Forest will become a firefly destination too.

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Photo (top): Fireflies sync up for a brilliant display in Great Smoky Mountain National Park (Credit: Radim Schreiber / fireflyexperience.org). To view more photos of the synchronous firefly displays in the Smoky Mountains, go here