On another June night, in 2012, a group of visitors arrived at Ken and Peggy Butler’s bed and breakfast, out past reliable cell service in Forest County, Pennsylvania. Peggy was a school therapist, Ken a money manager, and they had moved out into the northwest corner of the state for the quiet and the fly fishing.

These visitors were not the Butlers’ typical bed-and-breakfast guests. The roving band of firefly scientists lugged microscopes and butterfly nets into the Butlers’ garage, then spent the next six weeks venturing out in tick-proof gear each evening, surveying fireflies where the Butler’s grassy backyard melted into the half-a-million-acre national forest. What they found was nothing short of astonishing—a wonderland of evolutionary biology amidst the quiet, unimposing hills of rural Pennsylvania.

Scientists don’t know for sure when or why the first beings evolved to emit their own light. The leading theory holds that bioluminescence evolved on Earth even before widespread photosynthesis, half a billion to two billion years ago. The air then was mostly devoid of oxygen, which suited most organisms of the time, because oxygen—a very reactive substance—was toxic to them. To detoxify any oxygen they did encounter, this theory holds, some organisms evolved a chemical process that could consume any offending molecules while popping out a little bit of light as a harmless byproduct.

Whatever its primordial purpose, bioluminescence has since emerged or reemerged at least 94 times across the tree of life, according to scientists’ latest count. The specifics of how different single-celled organisms and larger creatures accomplish their own glow-up tricks vary, but a general pattern holds across most examples. Bioluminescent organisms like fireflies have enzymes called luciferases (“lucifer” in Latin meaning “light-bringer”) which they apply inside specialized lantern-organs, alongside a pinch of oxygen and a little bit of energy, to another class of compounds called luciferins. Et voila: a photon of light comes out.

Most creatures who adapt this ancient chemistry to their own ends reside in the ocean: electric-blue crustaceans, fish that use dim lights to cloak themselves from predators, and deep-sea squid that scintillate like alien spacecraft. A few, like New Zealand’s glowworms (Arachnocampa luminosa), live in caves. Fireflies, conversely, are easy to see, flickering at the edge of backyards, captured in jars, shining in the childhood memories of millions as a stand-in for nostalgia or wonder. Perhaps because they’re the type of bioluminescent creature people are most likely to encounter, fireflies hold a special allure—often they’re a gateway to an under-appreciated, imperiled cosmos of nocturnal biodiversity.

To date, scientists estimate the world hosts some 2,200 species of fireflies. Some are active during the day, communicating via pheromones. But the most well-known come out during the evening or night to inscribe bursts of light into the air like species-specific autographs. The researchers who first came to survey the species in the Butlers’ backyard included Lower, who was then a graduate student, and Lynn Faust, an independent naturalist and firefly expert. The team found at least 16 species in all, the insects living practically on top of each other.

Two species in particular stood out. The researchers spotted clouds of one famous and rare firefly, Photinus carolinus, which flashes in synchronous bursts, causing larger groups of them to light up in near-unison in a wave that move across the forest. Then they discovered the new species nicknamed “Chinese lanterns,” flying like lazy sparks above a campfire for long beats of electric lime green. Both these and the synchronizers, wrote Faust in the survey report, “easily reached the ‘WOW!’ level.”

For the Butlers, the choice now was whether the scientists should be vague or precise about the location of the firefly wonderland. “If you decide you don’t want to pursue anything with this, we will keep it quiet,” Faust told the Butlers. “You can just go about your lives as normal as possible.”

The Butlers evaluated their options. Make the report as specific as you like, they said. How many people could possibly come?

Faust knew the answer to that question. Her own path to the forefront of firefly science began not as a credentialed academic but as a young mother in 1992, when she invited scientists to her family’s cabin in the Great Smoky Mountains in Tennessee to study a spectacle her family had long referred to as “the light show.” As those scientists soon published, Faust’s family’s private light show was actually North America’s first proven example of synchronous fireflies.

Soon people wanted to see for themselves. Many people. The synchronizers in the Great Smoky Mountains National Park became an annual event on par with Fourth of July fireworks, drawing up to 26,000 tourists a year. Visitors clomped through the forest, often crushing female fireflies underfoot or disorienting the insects with their flashlight beams. “I have crouched in the dark woods, illuminated by the rhythmic flashes, and wept over the unintended consequences,” Faust wrote in her 2017 book Fireflies, Glow-worms, and Lightning Bugs, one of the few authoritative field guides to North American fireflies.

On the other hand, she felt, many of these clompers would otherwise never go out in the dark with eyes and hearts open to nature. Was sharing the Smoky Mountain fireflies with the world the right call? “It depends on which night you get me,” she told me recently.

Our effort to understand how quickly fireflies are disappearing is also hampered by our relative ignorance of them. North American fireflies spend the vast majority of their lives as larvae wriggling through soil, where they hunt down worms and snails, inject their prey with enzymes, and slurp up the resultant puddle of goo. Once they emerge as short-lived adults, some species
are known only by a specific flash that some naturalist described seeing in a dark jungle decades ago. When the IUCN published its first firefly conservation status survey in 2021, focusing on 132 species in North America, they found 18 at risk of extinction. But 70 more they categorized only as data deficient, meaning we don’t know enough about them to say how imperiled they might be.

“Compared to what the monarch people can do, it’s so sad,” says Owens. Unlike butterfly hobbyists, who go out in clubs during the daytime and have collected decades of data on population abundances, firefly surveying has historically been a solitary activity. “Each couple of decades you get, like, one eccentric person who spends every night in the middle of the woods,” she adds.

“Five years ago we basically knew nothing,” says Sara Lewis, a biologist at Tufts. For years, Lewis designed careful lab experiments to understand firefly reproductive structures and behaviors. Then, “a switch went off in my head and I was like, wait, what difference does it make to know [these specific details about] a group of animals that could be extinct in 50 or 100 years?” Today, Lewis co-leads the IUCN’s efforts keep firefly populations alive.

As some firefly populations fade to black, though, general and scientific interest is swelling. More people want to see fireflies for themselves, driving firefly tourism, and more scientists want to better understand firefly biology both for its own sake and for future conservation work. Perhaps the Butlers didn’t have to make the same stark choice Lynn Faust had made in the Great Smoky Mountains. Perhaps tourism and science could complement each other. Maybe people could love fireflies neither too little or too much but just the right amount.

At the same time, the Butlers built up closer ties with the scientific community, converting their B&B into something more like a hostel for visiting researchers. Among the scientists who kept coming back was Lower, who is studying the many firefly species that restrict their activities to the day and communicate with pheromones. Lower and her collaborators recently isolated the first known firefly pheromone, and she was at the Butlers’ in 2022 to determine what scents fireflies are using to attract one another and whether light and smell-based flirting are mutually exclusive.

Some of the most authoritative research on how artificial light stifles fireflies was also hosted by the Butlers. In recent years, light pollution ecologists have demonstrated that blue colors of light at night have a disproportionately negative impact on the nighttime ecology of many other species so far studied. When Owens came here to test the least harmful colors of artificial light for fireflies in 2019, though, she found that amber-colored lights—darlings of the dark-sky environmental movement because most species, humans included, seem less bothered by them—are especially disruptive to fireflies. Red lights are still a good choice, Owens says, but the best strategy remains the most obvious: just use light sparingly overall.

The research happening at the Butlers’ is just one part of a worldwide firefly renaissance. Setting aside habitat loss, light pollution, and pesticides, the known ranges of many firefly species and exotic behaviors seem to be expanding. Experts say that’s because more people are out looking. Starting from the “discovery” of synchronizing P. carolinus fireflies in the Smoky Mountains in the 1990s based on Faust’s reports, naturalists and scientists have recognized other P. carolinus outposts up and down the Appalachian Mountains. (The Xerces Society maintains a map of places that accept visitors to view these and other species.)

The same scientists who Faust had summoned to Tennessee later documented synchrony in another American species, Photuris frontalis, found in places like South Carolina and Mississippi, which soon drew their own research scientists and crowds, which in turn helped spark the passion of new enthusiasts. After surviving a life-threatening car accident, for example, the North Carolina State University entomologist Clyde Sorenson told me he pursued research on fireflies for the pure joy of it. In 2019, Sorenson documented firefly synchrony on North Carolina’s Grandfather Mountain, and has since been tracking down an undescribed “ghost” firefly species that emits faint green signals that can last as long as half a minute.

With firefly tourism on the rise as well, a team convened by Lewis published a set of recommendations in 2021 for how to manage the upswing of interest. While tourism is unlikely to lead to global extinctions, it can certainly extirpate local populations, she says. The final report recommends robust habitat protection and education programs, including etiquette guides. For guests, that means carrying no artificial light sources and staying on marked trails; for hosts, they mean limiting total visitor numbers, fencing off paths, and minimizing lighting. These are all steps that the Butlers have taken as part of their journey from wide-eyed enthusiasts to conservation advocates.