Synchronous Fireflies

Scientists don’t know why these rare synchronous fireflies, found in a section of the Great Smoky Mountains National Park, glow simultaneously.

GREAT SMOKY MOUNTAIN NATIONAL PARK — There is a reason that Great Smoky Mountains National Park continually sets records for the numbers of visitors that drive through its gates. 

Nine million visitors admired the grandeur of the roughly 522,000 acre park that straddles the Tennessee and North Carolina border in 2014. It is the most visited National Park. Tourists say it is beautiful, it is easily accessible and it is unlike anywhere else. They’re right. 

Simply put, there is no place on Earth that's the size of Great Smoky Mountains National Park, and in a temperate climate, that can match the rich biodiversity found here. 

“Because of all of the different elevation gradients, going from 800 feet to over 6,643 feet at the highest point at Clingman’s dome, we have a variety of climates in the park,” explains Dana Soehn, a National Park Service ranger. “So you can feel you have a low valley wetland area, or the really dry southern pine forest, and then as you travel up slope there’s a rich cove hardwood, and then a northern forest, where all of the sudden you’re at this Frasier fir, spruce fir forest at the highest elevation.” 

And along those gradients you find different habitats, and different amounts of rainfall and that allows you to have great spaces for a wide variety of plant and animal species to live. 

So far, a survey conducted by the National Park Service in partnership with biologists around the country has counted more than 20,000 different species in the park. Nine-hundred of those are new to science. 

And for two weeks every June, for only about two hours every night, in one small corner of the park, one of those species creates a kind of nocturnal magic. And it’s all about love. 

“The firefly display is all about courtship,” says Becky Nichols, National Park Service Entomologist in Great Smoky Mountains National Park. “It’s their way of finding each other and recognizing it’s the same species.” 

Picture a dark forest, with tiny pinpoints of light rising from the branches, twigs and leaves that carpet the forest floor. The lights begin moving, dancing and blinking. Suddenly, those random blinks begin flashing together. On and off, then on and off again. The flashes last for about six seconds. 

The forest transforms into a magical dance of tiny lights, set against a deep black background. The sound of crickets provides the music. 

This is the courtship dance of photinus carolinus, the synchronous firefly. Nichols has recorded 19 species of fireflies in the park, including photinus carolinus, but it’s one of only a few firefly species in the world that synchronizes its flash pattern. And the park’s synchronous fireflies weren’t discovered until 1994. 

“The male is the one you will see flashing and it does six to eight flashes, then dark, then repeats the pattern,” says Nichols. “The female will stay close to the ground and will respond with a double flash, and when they find each other they can reproduce and then they don’t live much longer.” 

All fireflies have a different pattern of flashing, and so to recognize each other in the dark, they have to have a specific pattern for each species that they can recognize. 

Some fireflies soar at different heights above the ground. Some fly in a specific flight pattern. The common evening firefly, which is found in the backyard, repeats an upside down ”J” pattern. But the synchronous firefly doesn’t have a pattern because its flash sets it apart. And like all fireflies, that light is created through a process called bioluminescence. 

The natural light show is one of nature’s amazing inventions. It’s a chemical reaction, and it’s incredibly efficient. Lots of light is produced but there is no heat generated. Fireflies combine the chemical luciferin with an enzyme called luciferase in the presence of oxygen. When it’s all combined in the abdomen of the firefly, light is produced. That means every time the firefly flashes, it uses a little more of the chemical. And the firefly grows up with all of the chemicals it needs to flash and find a mate. 

“They don’t feed as adults, so what they have in reserve is all they have,” adds Nichols, who is pointing to a synchronous firefly that is mounted under a microscope for study. On the firefly’s underside, in the abdomen, is a clearly defined three-chamber section where the light is produced. “And so once they do their flashing behavior and reproduce, that’s the end of their lifespan.” 

“It’s kind of a sad story in a way, but it’s also beautiful and unique,” adds Nichols. “I’ve never seen anything like the synchronous flashing these insects create.” 

The synchronous fireflies add to the uniqueness of the landscape that is Great Smoky Mountains National Park. 

“While we have a few valleys, primarily you are experiencing an incredible expanse of rich forest, some of which is ancient. In fact almost one-third of this forest has never been cut, so it’s an even richer area for discovering species,” Soehn says. "The fireflys are just another example of what makes this place so special.”

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