A new study shines light on how bug spray, flashlights, and foot traffic can spell disaster for the fragile creatures behind brilliant synchronous displays.

In 2012, firefly expert Lynn Faust made a surprising phone call to the owners of the Black Caddis, a bed and breakfast in rural Pennsylvania: There had been reports of the insects flashing in unison in the nearby woods, her team was coming to investigate, and they needed a place to stay. “They turned over all their rooms,” Faust remembers, “and their two-car garage, where we set up a laboratory filled with vials and microscopes and fireflies.”

Faust is a member of the Firefly International Research and Education (FIRE) team, and they were looking for Photinus carolinus, one of the few species of North American fireflies that are synchronous, meaning the males gather in large groups and flash simultaneously to court mates. Scientists aren’t sure why they do this, although it may be that male cooperation attracts a greater number of females and allows them to compare suitors.

After two weeks of field studies, flash timings, microscopic exams, and DNA analysis, the team confirmed what their report called “the robust and widespread existence” of Photinus carolinus. At the time, the only other known population of the charismatic bug in the US was in a small section of Great Smoky Mountain National Park, where thousands of visitors congregated each summer to take in the stunning light show.

Ken and Peggy Butler, the owners of the Black Caddis, saw an opportunity for their county, one of the poorest in the state. The next summer, they formed a nonprofit and hosted the first Pennsylvania Firefly Festival. They were blown away when 400 people attended. But three years later, the festival had swollen to 1,000 people in a single night, overwhelming their capacity to manage the crowds. “There were people running around the forest with flashlights,” Ken Butler recalls. “We knew we were making mistakes. We couldn’t maintain the festival, let alone the habitat.”

The Butlers were right to be distraught. This March, an international team of scientists released the first comprehensive study of firefly tourism, warning that the viewing events could very well extinguish the stars of the show. The insects are “not just something to gawk at,” says Sara Lewis, the lead author, a biology professor at Tufts University, and cochair of the International Union for Conservation of Nature’s firefly specialist group. “These are real animals.”

In the United States, firefly season begins in late May, when they perform their courtship displays and approximately 200,000 tourists head to the woods to watch. Globally, an estimated 1 million people travel to displays in at least 12 countries, a remarkable surge in interest fueled in part by social media. By conducting interviews and online surveys of scientists, tour guides, government officials, and independent entrepreneurs, Lewis’ team documented some of the risks crowds pose to fireflies.

Many species spend large portions of their lives under and on the ground, where oblivious tourists can trample them. Foot traffic can also compress leaf litter and erode soil, degrading habitat where larval fireflies grow and find prey. Light from flashlights, cameras, and phones can confuse them, disrupting the brief window for courtship and mating. And because fireflies use chemical cues in addition to bioluminescence to attract and choose a mate, excessive bug spray can disorient them.

The study offers anecdotal evidence of these problems from around the world. For instance, in Amphawa, Thailand, where male fireflies create dazzling displays in the mangroves along the Mae Klong River, fleets of motorboats and flashlight-wielding tourists have been responsible for wiping out an estimated 80 percent of the insect’s population. Excessive boat traffic also eroded the riverbanks, toppling the trees where male fireflies performed and washing away mud along the shoreline, essential habitat for larval fireflies.

In the tiny town of Nanacamilpa, Mexico, officials were overwhelmed by hundreds of thousands of tourists each summer, many of whom strayed from designated areas, unaware of the females (who are flightless in some species) that they were crushing beneath their sandals. At Congaree National Park in South Carolina, where synchronous firefly displays had once been a well-kept secret, rangers began receiving frequent complaints about habitat disturbance and light pollution.

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A female Synchronous Firefly (Photinus carolinus) perches on vegetation in the early morning.Photograph: Clarence Holmes Wildlife/Alamy

But Lewis doesn’t think tourists deserve all the blame. “Scientists have been really sucky about letting people know about the diversity and behavior of fireflies,” she says.

To help site managers protect fireflies while wrangling crowds, Lewis and her coauthors came up with a list of best practices. While courtship displays happen in midair, keeping people away from the ground is paramount, the authors say. That’s where fireflies spend months—sometimes years—in their larval stage. Site managers should also carefully regulate artificial light. If visitors must wear bug spray, they should apply it before leaving home to reduce its potency. To make sure that crowds get more than just a light show, tourism operators should invest in training guides who will accompany visitors, answer questions, and reinforce the value of conservation.

And there’s another hope: New populations of synchronous fireflies keep getting discovered. “They are not as rare as the public believes them to be,” says Clyde Sorensen, an entomologist at North Carolina State University, who points to newly confirmed populations in North Carolina and West Virginia. “I’m confident there are many other populations throughout Appalachia.”

Sorensen believes that opening up more sites to visitors “should be the goal,” releasing pressure on the handful of popular sites. “As long as people follow guidelines, it’s something they ought to see,” he says.

Lynn Faust, whose phone call to the Black Claddis eventually led to the Pennsylvania festival, agrees that people should get a chance to admire the fireflies. But, she says, “management does need to happen. It takes a good organizer—or 10—as well as knowledge about the fireflies, money, and a lot of time and effort. It’s not easy.”

The Pennsylvania Firefly Festival looks much different these days. Peggy Butler says the pandemic, which forced them to cancel the event in 2020, was a good excuse to “put the genie back in the bottle.” In recent years, they have implemented new protocols, including mandatory registration to reduce crowd size, tour guides to present educational programs, and bleachers to keep people’s feet off the ground. The 2021 festival will be more intimate than ever. The festivities will take place over two nights in June, strictly limited to 50 people per night. Forty-five more visitors will attend the festival’s new immersive overnight experiences, broken into groups of 15 and spread among three of the national forest’s campgrounds.

The Butlers feel confident that this pared-down format will protect the remarkable creatures they were surprised to find in their backyard. “Monetizing [the fireflies] was the first temptation,” Ken Butler says. “But we received this as a gift. And we want to pass it on as one too.”


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