Each year, spring beckons dynamic activity in the natural world. In the old Smoky Mountain settlement known as Elkmont, the transition from spring to summer arouses an extraordinary display of highly specialized firefly mating behavior: synchronized bioluminescence.
Known to many as "synchronized fireflies," these creatures (Photinus carolinus, belonging to the firefly family Lampyridae) exhibit immensely sophisticated "light shows," which in recent decades have received increasing attention from the general public.
Lynn Faust, naturalist and longtime Knoxville resident, is credited with bringing this seemingly far-out spectacle to the public eye. Though Photinus carolinus has existed for millennia, they somehow went unnoticed among researchers in the Appalachian region. "They were here long before us," Faust explained.
The Faust family owned property in historic Elkmont before the national park took over the land and remembers watching "The Light Show" as early as the 1950s. Coincidentally, during their last summer in Elkmont in 1992, a story was published on Asian synchronous fireflies, claiming that no similar species were known in the Western hemisphere. Immediately recognizing that Elkmont's fireflies were "synchronous," as described in the article, she began an extensive journey of research that continues today. Indeed, much of what is known about these critters can be wholly attributed to Faust's work.
In essence, the synchronized lighting display encompasses a very complex mating ritual. Males begin flashing late in the evening while females wait in the forest litter below. The pattern of male flashing distinguishes this species from other fireflies around the world. For a few seconds, males reveal a series of 6-8 flashes, followed by a period of darkness for roughly 8 seconds.
During this period of darkness, males anxiously await the females' responses coming up from the ground below. This allows a pattern of predictability for both males and females, which can help prevent predation or crossbreeding with other species of fireflies. Moreover, timing is affected by numerous factors, most notably temperature. When males detect the faint flash responses of the females, the rest is history — this species of firefly only lives for a few weeks, so there's no time to waste.
Most males guard their female counterpart until the sperm is transferred, thus ensuring his genes pass on to the future. Viewed at night in the woods, the eerie pulsation of wave synchrony is far more impressive than any modern light rig.
The lighting itself is dependent upon a reaction between luciferin and luciferase within the firefly's lantern, which is a part of their abdomens. The result, termed bioluminescence, gives off nearly 100 percent of energy as light. In comparison, light bulbs produce only a fraction of this energy, while the rest is emitted as heat. Because of this efficiency, the bioluminescence of synchronized fireflies is known as "cold light."
"These tiny little insects are eloquently designed to survive and mate," Faust observed. "We may think we're smart, but for every fact we uncover, 10 others remain unknown."
On average, the lighting displays last for roughly five days, ending with "peak" flashing behavior.
This year, Faust expects flashing to begin sometime in mid-June. Impressively, she uses the degree-day systems to predict flashing occurrence based on temperatures. Each year, thousands of people travel to the park specifically to observe this event. Consequently, the Park Service now offers shuttle rides to and from Elkmont to experience the natural light-rhythms of this remarkable species.
In spite of the natural and seemingly innocent beauty, Faust reinforced the fact that nature is not a "dream world." "They may flash and get eaten by an impersonator," she explained.
Zach Marion, a Ph.D. student in ecology and evolutionary biology, reflected on the complexity of the predator-prey relationship among fireflies. "The real cost to flashing is in the risk of predation, as it makes the flasher noticeable to visual predators," he said.
"Most fireflies are protected from generalist predators like bats, birds and many insects by a complex cocktail of cardiac steroids. In high enough concentrations, these can stop a predator's heart, induce kidney failure, and cause violent vomiting. I can tell you from experience that they really taste awful. My research involves trying to understand why there is such a diversity of chemical compounds overall, and how that complexity evolves at the individual, population, and species level."
Known as "femme fatale" lightning bugs, Marion went on to describe a specific worry for Elkmont's synchronized fireflies.
"While most predators don't like fireflies, a group of fireflies in the genus Photuris does," he said. "Photuris do not make the cardiac steroids themselves. Instead, they (the females especially) mimic the flashes of females from other firefly species. When the males come to mate, the Photuris eat them, stealing their defenses for themselves and passing them on to their offspring for protection."
The fact that these animals still exist is a testament to the importance of our national parks and protected lands. Ranging in distribution from northern Georgia to Pennsylvania and New York State, and preferring elevations of roughly 2,000 feet, protected habitat has allowed this otherwise conspicuous animal to thrive.
Nonetheless, increased development in rural areas near the Appalachians has the potential to disrupt critical habitat for these fireflies. Faust offered several simple measures that could minimize mating disruption in fireflies. Most importantly, she noted that, "Be aware of your outside lighting at night. This can devastate mating displays. Lights left on can cause populations to disappear."
On the annual festivities at Elkmont, Faust observed, "I had no idea how popular it would become. It's pretty cool to witness several thousand people stepping out of their comfort zones to experience this natural beauty, especially when these days the majority are at home looking at computer and TV screens. It has brought people, both young and old, together in nature at a time when we've become very disconnected from it. None of us can protect nature unless we understand it."
For information regarding this year's events, head over to www.nps.gov/grsm/naturescience/fireflies.htm/.