Fireflies in Tennessee: Tourism, Light Shows & Algorithms

January 25, 2013

A TRUISM IN TRAVEL is that on your first trip to a destination you learn what you should have done or gone to see. Sometimes you get back to do or see it, and sometimes you don’t. It is even more difficult, for scientific research as well as travel, to be there to witness rare, occasional or brief seasonal events in the life of a plant, animal or region. For example, I was in New Zealand the wrong season, and missed their famous glowworm (firefly) caves. Too much is happening and the world is too big to see or do everything; and some things are out of our vision, anyway; being too big or too small, too distant, or in the ultraviolet, infrared or some other electromagnetic frequency beyond our immediate sensory perception.

Viewing firefly (aka glowworm; lightning bug, firefly beetle, hotaru) photonic light displays at their rhythmically flashing best means being in the right place at the right time. Many of the world’s 2,000 known fireflies species lack the night fire, and are rather anonymous. Some glow as eggs and larvae (presumably to ward off predators), and as adults (advertising for mates). But most of the year, even the best flashers remain hidden (often as eggs, larvae or pupae) in the soil. More rarely, some esteemed Asian species have underwater larval life stages living in rivers, streams, wetlands and rice paddies and providing biocontrol of freshwater snails. The genji-botaru and heike-botaru fireflies (hotaru), celebrated since the 8th century in Japanese poetry (e.g. Man’yoshu) as early-summer “little lights darting about in the night,” are also icons of water purity.

Enchanting traveler’s tales involve the synchronous rhythmic flashing of many thousands, perhaps millions, of fireflies as far as the eye can see across the landscape. “Over the past four hundred years many anecdotal accounts of synchronous flashing of myriads of fireflies in trees in Southeast Asia have been scattered through travel books,” wrote pioneering firefly scientist, John Buck, who got started wondering about fireflies as a kid and advanced his studies working with his wife, Elisabeth, during summer vacations from his main work at the National Institutes of Health. “Pride of place in antiquity passes from Kaempfer’s (1727 Dutch physician’s book: The History of Japan (With a Description of the Kingdom of Siam)) description of synchronized flashing at the classic locality, the banks of the Chao Phraya (Meinam) River in Thailand, to Hakluyt’s (1589 book: A Selection of the Principal Voyages, Traffiques and Discoveries of the English Nation) account of what was probably the same phenomenon, as seen by Sir Francis Drake’s 1577 expedition: ‘a certaine little Island to the Southwards of Celebes…Among these trees, night by night, through the whole land, did shew themselves an infinite swarme of fiery worms flying in the ayre…make such a shew of light, as if every twigge or tree had been a burning candle.’”

Synchronized firefly flashing was late being recognized in the Americas. “Early in this century sightings of synchrony among flying fireflies in American meadows began to appear,” wrote John Buck in 1988. “No reasonable explanation of the behavior was offered: in fact a strong aura of incredulity or even mysticism pervaded the subject.” Indeed, when John Buck started studying fireflies in earnest in the 1930s: “The fast film, laboratory oscilloscope and image-intensifier that would eventually confirm and dissect synchrony were, like the jet airplane…still in the future…Today the phenomena has been photographed, charted, and videotaped…”

“The modern study of synchrony in fireflies dates from 1968, when John and Elisabeth Buck used cine photography and photometry to demonstrate that a certain number of Southeast Asian firefly species flash in rhythmic synchrony,” wrote Jonathan Copeland and Andrew Moiseff, who “used videography, photometry, computer-shaped LED flash, and flash entrainment experiments” in their own studies of flash rhythms in the synchronous firefly, Photinus carolinus, a popular tourist attraction in Tennessee’s Great Smoky Mountains National Park.

When the Entomological Society of America (ESA) met for its annual meeting in Knoxville, TN, in November (2012), the synchronous fireflies famous for what locals call “The Light Show” were slumbering about 50 miles away in the former logging town of Elkmont, which was swallowed up (residents sent packing) into Great Smoky Mountains National Park. “Huge numbers of male fireflies flash synchronously, dazzling the human spectators and drawing female P. carolinus for the purpose of mating,” wrote Lynn Faust of the Great Smoky Mountains Conservation Association, a former Elkmont resident, who along with local volunteers have collected 20 years of firefly data; aided by Paul Weston (Charles Sturt University, New South Wales, Australia) and other scientists.

“The display lasts only several days to slightly over a week, which means that the ability to predict its occurrence is of critical importance to the National Park Service, which organizes shuttle buses to ferry visitors from parking areas to the ecologically sensitive areas where the fireflies put on their display,” Faust and Weston told the ESA annual meeting. For the 10-day peak Light Show display, there have been up to 26,000 tourists. “Predicting the timing of this natural phenomenon is of equal importance to the researchers and naturalists who study its annual occurrence.”

In his Newbery Medal winning book (1989), Joyful Noise: Poems for Two Voices, poet and children’s book author, Paul Fleischman, calls fireflies: “…glowing insect calligraphers practicing penmanship…Six-legged scribblers of vanishing messages, fleeting graffiti…Fine artists in flight adding dabs of light, Signing the June nights as if they were paintings…” A description hard to top, even with the many fine firefly night light paintings from light shows around the world displayed on photographs on the Internet and in YouTube videos.

“The synchronous firefly Photinus carolinus (Green) of the moist cove hardwood forests of the Great Smoky Mountains National Park attracts much public attention during its spectacular month-long mating display known as The Light Show,” writes Lynn Faust in the Florida Entomologist. Besides the human tourist hordes, predatory biocontrol species also seem attracted to The Light Show: “Orb-weaving spiders (Araneidae) prey on P. carolinus. Late at night, after all courtship flashing had ceased, often the only lights visible were the rhythmic distress flashes or the steady glow of fireflies caught in webs. In addition, harvestmen (Phalangiidae) often were seen carrying glowing pupae, adult fireflies, or only the still glowing firefly lantern…local Photuris fireflies readily eat captive P. carolinus and regularly fly and signal within the dense display areas of male P. carolinus… Phorid flies (Apocephalus antennatus Malloch) parasitize Photinus fireflies by ovipositing eggs within the firefly’s body…” So, with the risk of being eaten by predators and becoming part of the greater ecological food chain during the short performance season, the life of an adult firefly Light Show performer must be as tough as it is brief.

Over the past two decades, lifelong firefly-enthusiast Faust and the Great Smoky Mountains Conservation Association volunteers collected data on “four landmark phenological events,” namely: 1) male emergence (date on which first flashing male fireflies are observed); 2) “good” display (date synchronized flashing by males is seen over wide areas; not just isolated patches); 3) female emergence (date of first female flashing in response to males; doublet flashes in leaf litter or low vegetation); and 4) peak display (final night of maximum male flashing displays; determined in retrospect, usually after a sudden fading out of The Light Show).

“A degree-day model based on a base temperature of 50 F (10 C) and a seasonal starting date of March 1 has resulted in remarkably accurate predictions of four landmark phenological events for Photinus carolinus,” Faust and Weston told the ESA. “This predictive ability has proven very helpful for timing research visits to field sites, and will be a valuable tool for the National Park Service when scheduling visits of thousands of visitors to the Smokies Mountain National Park to witness the Light Show.” The better the prediction of when “The Light Show” will occur, the more likely researchers, tourists and travelers will come away satisfied; versus feeling like they missed out.

“The Light Show is the name given by locals in the Smoky Mountains to the annual synchronous display of male P. Carolinus,” Faust and Weston told the ESA. “The males produce a string of about 6 flashes over 3-4 seconds, then remain dark for 6-15 seconds. Remarkably, these fireflies synchronize their flashes and dark intervals with those of their neighbors, which leads to visually striking displays stretching as far as the eye can see into the wooded hillsides and glens of the Smoky Mountains. The display can last for 2 hours or more on peak nights.”

The mathematics or calculations behind degree days (aka day-degrees, growing degree days, heat sums, thermal units, threshold temperatures) can be a bit tedious, but degree days are basically just a way of calculating the impact of temperature on a life process (or physiology). Degree days are used in botany, horticulture and agriculture to predict a range of phenomena, including flowering times, as higher temperatures mean plant enzymes are more active. Insects are also temperature-dependent creatures. Thus, degree-day models work to predict firefly adult emergence and light show times. Similarly, degree-day models can help time pest control actions by predicting the egg hatch of the codling moth, the proverbial worm inside the apple.

Raymond Bonhomme nicely sums up the agriculture origins of the degree-day concept: “The ‘degree-day’ unit stems mainly from the relationship between development rate and temperature. It was Re´aumur (1735) who first laid the basis of this notion: ‘The same grains are harvested in very different climates; it would be interesting to compare the sums of heat degrees over the months during which wheat does most of its growing and reaches complete maturity in hot countries, like Spain or Africa … in temperate countries, like France … and in the colder countries of the North,’ (original text in Old French: Durand, 1969). Even if the exact vocabulary was not correct (what is a sum of heat degrees?), the concept of a relationship between the development rate of crops (here the sowing to maturity period) and temperature was born. Hundreds of works have set about using, proving, or even disproving this idea…”

Degree days are only a warm-up exercise for mathematicians and computer scientists studying the synchronous rhythms and periodicities of fireflies. Indeed, synchronous flashing in fireflies may have similarities to other physiological events, like the human heartbeat (cellular coordination) or the schooling and swarming behaviors of fish and birds. No doubt some envision coordinating the actions of armies of drones or robots, though the Ant Colony Optimization (ACO) or Particle Swarm Optimization (PSO) algorithms might be better for that. Rather than being the dark warlike side of the light show, this work could also do great good in helping fight diseases involving coordination at the cellular or other levels, aiding theatrical productions or designing swarms of robotic devices for hazardous situations like fighting toxic disasters.

“Rhythmic communal synchronization occurs in body movements and sound production of a few insects and other arthropods,” wrote John Buck in 1988. “It is also typical of many human activities—e.g., dancing, the spontaneous rhythmic applause clapping by Russian opera, ballet and circus audiences and, notably, music. Even conducted orchestral music involves a large element of mutual cueing between performers.”

Hearing about the Firefly Algorithm, the mental lights flashed that it was perhaps created by Rufus T. Firefly, President of the bankrupt country of Freedonia, played by Groucho Marx in the 1933 USA movie, Duck Soup. But the Firefly Algorithm (FA) and the Improved Firefly Algorithm (IFA) are being studied by computer scientists and mathematicians trying to solve difficult optimization problems like “the famous economic emissions load dispatch optimization problem,” which is “one of the key problems in power system operation and planning in which a direct solution cannot be found.”

The Firefly Algorithm, developed in 2007 by Cambridge University’s Xin-She Yang, is simply a set of rules or problem-solving steps, in this case inspired by nature and programmed for computers based in part on the details of flashing firefly lights, an insect social or swarm activity. “Although the real purpose and the details of this complex biochemical process of producing this flashing light is still a debating issue in the scientific community, many researchers believe that it helps fireflies for finding mates, protecting themselves from their predators and attracting their potential prey, said Theofanis Apostolopoulos and Aristidis Vlachos of the University of Piraeus (Greece) in the International Journal of Combinatorics. “In the firefly algorithm, the objective function of a given optimization problem is associated with this flashing light or light intensity which helps the swarm of fireflies to move to brighter and more attractive locations in order to obtain efficient optimal solutions.”

Besides energy conservation algorithms for heating, ventilation and cooling (HVAC) systems, understanding firefly light production is a path to more energy-efficient household and industrial lighting. “The firefly produces its narrow-spectrum 560 nanometer light just like a chemical laser, but with even greater control,” writes Extreme Tech columnist, John Hewitt. “Understanding firefly scales as tiny prisms that change the way light impinges on an interface and creates new sharp-edged channels through which light can diffuse lets us make LEDs more efficient.” Indeed, mimicking firefly light transmission can boost light production from GaN (Gallium Nitride) LEDs by 55%.

As the Ohio State Parks web site notes in their succinct discussion of firefly bioluminescence chemicals, luciferin and luciferase: “Scientists are still not sure exactly how fireflies control their lights, but they have found many important uses for the chemicals luciferin and luciferase. Since living cells have ATP and oxygen, researchers can add luciferin and luciferase to detect harmful bacteria in food, milk or water. The two chemicals are also used for special electronic detectors used in spacecraft to look for earth-life forms in outer space! Luciferin and luciferase are also being used in research on human diseases such as cancer, multiple sclerosis, cystic fibrosis, and heart disease. Firefly technology has also been used to produce safer, cold light for flashlights, flares and holiday lights.”

This is only the tip of the iceberg in innovation from studying fireflies. Just something to think about next time you are out watching fireflies, whether in your backyard, the Great Smoky Mountains or anywhere else on the planet.