Deep in the woods on a warm summer evening, a species of beetle signals its mate with a flash pattern unique to the Great Smoky Mountains National Park. Synchronous fireflies (Photinus carolinus), or lightning bugs as some Appalachian natives know them, are one of at least 19 species of fireflies that live in the park and the only species in North America with synchronized flashing light patterns.

Becky Nichols, a park entomologist, first learned about the synchronous fireflies in 1998, shortly after she started working in the park.

“The fireflies were well known by the local community at Elkmont when people still lived in the area,” says Nichols. “It was quite amazing the see the display for the first time with just a handful of other local people that knew about them at the time.”

The early summer lightshow is now a tourist destination. People from all over the world travel to the park in early June to experience the magic these Appalachian lightning bugs offer for one week each year. At first, people flocked to Elmont by the hundreds – parking their cars on the side of the road and trampling through the forest to find their perfect viewing spot.

“There were too many vehicles trying to come in and out of the relatively small area, cars would be parked in precarious places, headlights and flashlights were interrupting the flashing behavior, and people were going off trail, endangering themselves and likely stepping on the female and larval fireflies,” says Nichols. “In 2006, we began shuttling people to the site, so it is much more controlled now. Disturbance to the fireflies is minimized and the visitor experience is much improved.”

Park officials close the road into Elkmont for the viewing period and, during the eight-night event, between 800 and 1,000 people view the synchronous fireflies each night. In order to streamline the ticket application process, park officials implemented a lottery system for viewing in 2015. Each year, in mid- to late-April, dates for the synchronous firefly display are announced on the park website, social media channels, and through a press release. A few days later, the lottery opens for four days, which allows applicants to enter their information and choose two preferred dates to attend the event. When the application period ends, a computer chooses names randomly and winners are notified within 10 days.

“In 2019, there were nearly 29,000 applicants for the 1,800 tickets available,” says Nichols.

Determining Peak Display Period

Lynn Faust grew up spending her summers at a family cabin in Elkmont.

“As a child, I was no different from any other East Tennessee child, chasing lightning bugs at sunset, wondering at their funny smell and bright colors and magical flashes,” says Faust. “We enjoyed the wonderful light show from our big, screened-in porch each summer. We talked about them and their beautiful synchrony and waves on the hillside and understood this particular pattern was not in the valley at our homes in Knoxville.”

When the park took her family cabin in Elkmont in 1992, Faust was determined to learn more about the synchronous fireflies. She began her journey that has taken her all over the United States, Canada, Central and South America, Asia and Europe conducting research projects, participating in symposiums, and delivering talks about fireflies.

“Like everyone initially, my family and I thought lightning bugs were all the same,” says Faust. “Now I know better!”

At first, Faust traveled 120 miles round trip from her Knoxville home to Elkmont late at night to determine if the synchronous fireflies had started emerging. When she began working with film crews and other researchers, she needed a better process and used phenology – or calendar plants – to keep track of what plants began to bloom and which insects emerged in the woods around her Knoxville home at the same time the P. carolinus began coming out.

“When we had the cabin, we simply enjoyed the light show each summer with little attention paid to exactly when it occurred,” says Faust. “I needed to first understand their entire lifespan and the fact there is an actual peak. No one knew this at the time.”

In addition to phenology, Faust used historical records from thousands of pages of her own field notes and historical weather records of rainfall, temperature, snow and other weather events collected by scientists with the National Weather Service and National Oceanic and Atmospheric Administration. By 1993, Faust and two other scientists who study synchrony acquired a research permit to observe the fireflies. In order for fireflies to be considered synchronous, their flashing must be rhythmic, repetitive and show a tendency for unison. After observing the Elkmont fireflies, they determined that P. carolinus fit the bill. Until they published their research, only a handful of reports of synchronous fireflies existed in North America.

The peak display period for the synchronous fireflies is determined by calculating degree days, which is essentially a measure of maximum and minimum air and soil temperature data from the Elkmont site. Temperature determines the rate of development for the larval stage. The degree day method is used to predict the emergence of a variety of species of insects, include the synchronous fireflies.

“We all understand the concept of ‘early spring’ and ‘late spring,’” says Faust. “That is all degree days are – they measure the accumulated heat of the season. The warmer it is the faster or sooner the insects emerge.”

Faust and colleague Paul Weston developed the degree day formula for the synchronous fireflies in 2009 and Nichols has used it ever since to set shuttle dates for the synchronous firefly show.

“After calculating the degree days up until a certain point, we can then project further based on predicted temperatures, to arrive at the date range when the peak display will likely occur,” says Nichols.

Over the years, synchronous fireflies have peaked as early as mid-May and sometimes later in June. The 29-year-average peak at Elkmont, however, occurs approximately June 6 – 9.

In 2017, Faust’s nearly 30 years of firefly curiosity culminated into the first-ever comprehensive firefly field guide for the eastern half of the United States and Canada. Fireflies, Glow-worms, and Lightning Bugs contains more than 70 species of fireflies, including historical backgrounds, a chart documenting the flash pattern of individual species, and photos that illustrate distinguishing physical characteristics of these magical insects.

The Science Behind the Magic

While the flicker of a firefly in the night sky can seem like magic, it all comes down to a chemical reaction inside their bodies. The basic ingredients are oxygen, calcium, an energy-carrying molecule called adenosine triphosphate, and the chemical luciferin, a light-emitting compound. When combined in the presence of luciferase, a bioluminescent enzyme, light is produced. It does not release heat like a light bulb, but rather, fireflies produce a cold light and do not lose a lot of energy during the process. The type of light they produce is call bioluminescence, which also occurs in marine animals, fungi and bacteria.

Fireflies light up for several reasons, but mostly it is about communication and attracting a mate. The males produce a signature flash pattern only females of his own species can identify. During the firefly show at Elkmont, visitors witness thousands of flying males flash a pattern of six quick flashes followed by six seconds of darkness to court the females hidden in the leaf litter. When she makes her decision to choose a mate, the female firefly sends a paler, short, simple and subtle response by pointing her abdomen to her courting male. The synchronous courtship display continues for about two hours.

“If you’ve ever been lucky enough to experience a peak night, you would understand why the synchronous firefly display is such a popular event,” says Faust. “I think people love that it is a magical, beautiful display completely orchestrated by Mother Nature. Once someone has experience it, they want to share it with a loved one the next year. I love seeing so many people leave the comfort and safety of their living room and electronic devices to come to the woods and relax in the dark, quietly anticipating the magical light show.”

Environmental Factors

Environment plays a key role in the firefly show at Elkmont. P. carolinus prefer humid, dark and clean environments for their courtship and the Great Smoky Mountains National Park, which is similar to a temperate rain forest, is prime real estate.

Habitat destruction, however, is one of the greatest threats fireflies face in an increasingly developed world. The lifecycle of fireflies is a full year and much of it is spent in the larval stage. Once they mature into adults, they live for only about 21 days.

“Firefly larvae are predators and therefore need a diverse array of prey, which typically can be found in an undisturbed forest floor, but development has caused much of this type of habitat to disappear,” says Nichols.

Another threat to fireflies is light pollution. Due to the fact a successful courtship depends on a female being able to see the male’s flash patterns, too much human-caused light can disrupt their communication. This will lead to lower reproduction success and declining numbers of fireflies worldwide.

“Lightning bugs are an indicator species, or a canary in a coalmine,” says Faust. “If they begin to disappear from sites where they were previously abundant, something is very wrong. They are part of the wonderfully complex web of life in the Smokies.”

Preserving the Magic

Firefly populations are declining worldwide, but these charismatic creatures – a rare quality among insects – are an excellent example of a flagship species that can help educate people about the importance of insects in a healthy ecosystem.

“Humans can help fireflies thrive by considering the habitats required for them to complete their lifecycle,” says Nichols. “Minimal or no lighting at night will benefit not only fireflies, but other nocturnal animals as well. Also consider the pesticides you use and always follow label directions to avoid harmful effects on non-target insects, such as fireflies and pollinators.”

Observing firefly health in the park is an important piece of the conservation puzzle. Will Kuhn, a scientist with Discover Life in America (DLiA), helps monitor the synchronous firefly species and the blue ghost fireflies. He also works with researchers like Faust to conduct studies in the park.

“We manage the park’s All Taxa Biodiversity Inventory, under which 10 species of fireflies have been added to the park’s list since the project started in 1998,” says Kuhn. “There are currently 19 firefly species known to occur in the park and another five or so that are likely to live there that we have not yet discovered.”

Kuhn, who grew up in Texas, did not see many fireflies around his home. When he visited family in Nashville during the summer, he was overwhelmed by how many fireflies he saw.

“I was drawn in by their magical display as a kid and later, as an adult entomologist, came to the realization the typical fireflies I was seeing were actually a number of different species,” says Kuhn.

Kuhn and his colleagues at DLiA help promote the synchronous fireflies and educate the local community about the species as part of the rich biodiversity of the Smokies. While they do not play a direct role in the activities for the synchronous light show, they do want to work with partners in the park and the Great Smoky Mountains Association to educate park visitors about the fireflies of the Smokies and their place in the larger biosphere in Southern Appalachia.

“Fireflies represent an interesting paradox,” says Kuhn. “They are well known in a broad sense, but poorly studied in terms of their biodiversity. Nearly everyone in the United States, and probably most people across the world, have seen or heard of a firefly. Their magical bioluminescence is something we are drawn to, something of legend. And yet, it’s surprising how poorly they are studied.”

As the most visited national park in the country, the Smokies provide an opportunity for scientists like Faust, Nichols and Kuhn to educate millions of people around the world about the importance of fireflies and the role humans play in their conservation. Fireflies exist on every continent except Antarctica. There are an estimated 2,000 species worldwide and more than 125 species in North America.

“Any one of these species may be on the verge of extinction and we barely even know they exist, much less interact with the species around them and how key they might be for keeping their ecosystem in balance,” says Kuhn. “In this sense, fireflies are the poster child for a wider problem in biodiversity. We need to know the organisms that inhabit this planet to know how they function as part of the bigger picture. Time is running out for many species as humans are causing irreversible damage to our ecosystem.”

Every individual can take small steps right now, however, to help the fireflies in their backyard. Turn off outdoor lighting, such as decorative lights or floodlights, when they are not in use. Limit the use of pesticides and herbicides and consider leaving a portion of the backyard to nature to help create habitat for fireflies and other flora and fauna.

“I see over and over again the importance of green spaces like city parks, nature centers, large cemeteries and even railroad right of ways play in preserving our various firefly species,” says Faust. “Our system of state and national parks are absolutely critical at every level in preserving our amazing diversity of life.”

Faust, Nichols and Kuhn and others will continue their work to discover life in the Smokies and keep the firefly population thriving for future generations to experience the magic so many have come to love and cherish as part of a summer experience in the Smokies.

Originally published in Smokies Life Magazine, Volume14, #1

Photo by Radim Schreiber, FireflyExperience.org