Close your eyes for a moment and think about your favorite childhood memories. If you grew up in the eastern portion of the country, chances are good that one of those memories involves staying up past your bedtime and chasing fireflies around the yard. Sometimes you'd stuff as many as you could in a mayonnaise jar and keep it with you that night in your bedroom. Those "natural lanterns" were the source of endless fascination for our little minds and, occasionally, consternation from our parents when the captive critters staged a jailbreak.
More than 2,000 species of firefly live throughout the world. In the United States, most fireflies live in the central and eastern states, with some 40 different kinds occurring in North Carolina. In the South, people call them "lightning bugs," although most scientific literature uses the term "fireflies." Like all living creatures, each firefly species has a preferred habitat and exhibits unique characteristics. Some live most of their lives in the treetops, while others live in swamps. Some fly high in the sky, while others hover just above the ground. One thing all fireflies have in common is that they are neither flies nor bugs (in biological classification the term "bug" refers to a particular type of insect and is not used generically). Fireflies belong to the Lampyridae family, which is a type of beetle.
As a child, I did not clutter my mind with questions about scientific classification and I did not ponder how or why a firefly produces light. The fact that these little flying insects lit up was all the information I needed. But as I began to study and photograph nature as an adult, I wanted answers for those questions. The answers, I learned, were every bit as fascinating as that mayonnaise-jar lantern sitting by my bedside.
In the 1950s, researchers at Johns Hopkins University paid a penny apiece for every live firefly they could get their hands on, providing many Baltimore kids their first taste of entrepreneurship. Researchers at the university used these specimens to discover that the light-producing mechanism involves the chemical luciferin, which, when oxidized, causes the release of energy in the form of light. The firefly's abdomen contains luciferin, as well as the chemicals luciferase, magnesium, and adenosine triphosphate (ATP). In simple terms, when the firefly sends oxygen (the insect's "signal") to the abdomen, the oxygen combines with these chemicals and transforms the luciferin into an unstable, high-energy state. The instability causes it to revert to its normal state and as it does, it gives off energy in the form of light. This chemical reaction-producing light by a biological process-is called "bioluminescence." The light produced by bioluminescence is one of the most energy-efficient processes known, with nearly 100 percent of its energy given off as light. By contrast, a typical incandescent light bulb gives off about 10 percent of its energy as light, with the other 90 percent wasted as heat.
The early studies at Johns Hopkins and subsequent research by other scientists explains the "how" of the chemical reaction that produces light, but to answer the question of "why," researchers had to get out in the field and observe the insects in their natural environment. What they discovered is not that surprising, considering that in the plant and animal kingdom, some of the most colorful and bizarre phenomena all have one thing in common: attracting mates. Normally, only the males fly around and flash, while females sit on the ground or in brush or trees and respond to the flashes given off by the males. Each firefly species has a different flash pattern (called the "flash code"), which allows members of the same species to locate one another. After the male flashes, the female signals her receptiveness with her own flash code.
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Research performed within the past couple of decades has shown that a firefly's flash code is much more complex than originally thought. For example, certain carnivorous female fireflies use "flash code mimicry" to lure unsuspecting males of different species so they can eat them. Males are understandably cautious when responding to a female flash code and instead of flying directly to the female, they land a few feet away and cautiously crawl to her. Some males also use trickery themselves by producing flash codes to mimic the prey of females from their own species. The males effectively fool the females into thinking they're about to receive a tasty meal, when in fact the approaching male is one of her own species intent on mating.
Understanding the full complexity of flash codes is not a task for the average firefly enthusiast to undertake, but understanding that all those flashes have a meaning-and are not simply random blinks of light-makes witnessing the spectacle even more enjoyable. However, no amount of foreknowledge or explanation can prepare you for one of nature's utterly fascinating spectacles: the synchronous flashing of hundreds of fireflies in Great Smoky Mountains National Park.
That's right, the fireflies at one little spot in the park all flash in perfect synchrony, as if directed by a master conductor. Imagine standing in a field at the edge of a hilly wood. You're staring at one small section where everything is totally dark, and then in an instant a hundred fireflies flash at once. Now imagine following a "wave" of these flashes down the hillside, much like the arm waves you see at football stadiums. One witness described it as a "waterfall of fireflies."
The Smokies' spectacle occurs just over the state border on the Tennessee side of the park (incidentally, Tennessee's state insect is the firefly) and researchers have studied it since the early 1990s. In the 1990s, some reports claimed that the only other documented occurrence of synchrony in firefly flashing occurred at a sight in Southeast Asia, which made the Smokies' discovery the first one in North America. Even today some accounts still state that these are the only ones in the world. However, there are several other locations where synchronous behavior has been observed, including other locations in the Smokies, in North Carolina, and in Georgia. Some of these discoveries were made even before the well-known Smokies discovery. In a 1990 article in Wildlife In North Carolina, David Lee writes of observing this behavior in his backyard. He reported the activity to an entomologist, who related that the fireflies in Lee's backyard and a species in Florida were the only ones in North America known to exhibit synchronous flashing.
Firefly research has contributed to more than just a better understanding of the flashes. Since luciferin reacts only in the presence of ATP, and since ATP is present in all living cells, the process of bioluminescence has many practical uses. It is commonly used to test for bacterial contamination in food and water and it is being used in cancer research. Bioluminescence may even be used one day to test for life on other planets. If luciferin is mixed with the soil from another planet, any light emission would indicate the presence of ATP, and therefore, living cells.
In North Carolina, you can observe many different types of flashes given off by the various species. Probably the most commonly observed species in the state is Photinus pyralis, (interestingly, few fireflies have universally accepted common names) which flies over lawns and fields and flashes in an obvious "J" pattern. Some species flash in brief bursts, while others produce a continuous flash for several seconds. The best places to see several different species at the same time is where different types of habitat occur close together. Overgrown fields, manicured lawns, brushy streambanks, hilly woods, forest edges, swamps—all provide habitat for different species. If you live in a new subdivision, you might see only Photinus pyralis, but take a drive in the country and you'll find many others.
In North Carolina, fireflies usually start flashing around the first week of June, and depending on the species, the flashing can continue until the onset of cool weather in the fall. However, prime firefly viewing occurs from mid- to late June.
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"Why, I remember when this place was just lit up with fireflies." I hear this often from older people. There appears to be no question that firefly populations have declined, but I am not aware of any definitive studies that have confirmed this. It seems likely that development and pesticide spraying has had a negative effect on fireflies, just as it has on virtually all of our native flora and fauna. With development comes increased light pollution, which may affect the firefly's ability to use flash codes for finding mates. Another possible cause for decline is collecting from the wild. One company in Missouri has purchased tens (maybe hundreds) of millions of field-collected fireflies over the past couple of decades and, after processing the bioluminescent chemicals, sold them for research and commercial applications.
But perhaps there is another factor, one that has nothing to do with reduced numbers, but one that affects the numbers seen. In today's fast-paced world of computers, iPods, cell phones, and houses crammed onto quarter-acre lots, people just don't seem to connect with the outdoors as they used to. Back before all these distractions, and before air-conditioning became as common as the kitchen sink, people spent more time outside. Even in many urban areas, the fireflies are still there. Maybe not in the numbers they used to be, but they're out there.
This summer, why don't you relive those childhood memories? Go outside and chase some fireflies. And don't forget the mayonnaise jar.
Fireflies in the Garden by Robert Frost
Here come real stars to fill the upper skies,
And here on earth come emulating flies
That, though they never equal stars in size
(And they were never really stars at heart),
Achieve at times a very star-like start.
Only, of course, they can't sustain the part.
Childhood Fun with Lightning Bugs
Remember when we punched that jar lid full of holes so our lighting bugs could breathe? Well, it turns out that we weren't doing the critters any favor and we may even have contributed to their premature death by drying them out. That jar has plenty of air, so when your child goes out to catch fireflies, make sure there are no holes in the lid. And to help keep the lightning bugs moist, you can place an apple slice or moistened paper towel in the jar. Also, throw in some leaves or grass to give the fireflies something to crawl on.
While your children are having the time of their lives, you can use this opportunity to teach them a lesson in environmental responsibility. Teach them to handle the fireflies carefully and that they must let them go in the morning to resume their lives.
The Light Show in the Smokies
The synchronous firefly show in the Smokies has become extremely popular within the past few years. The Smoky Mountain Field School has an annual class titled "The Light Show in the Smokies." Dr. Jonathan Copeland, who first documented the synchronous behavior, leads the class. Participants spend the daylight hours in the classroom learning all about fireflies and synchronicity, and they spend the evening witnessing the "show."
Contact the Smokies Field School at http://www.outreach.utk.edu/Smoky/default.html.
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The Capitol of Fireflies
Boone, North Carolina is known as the "Firefly Capitol of America." However, the moniker is largely symbolic, as fireflies are no more common in Boone than in other areas of the state. The town once held an annual "Firefly Festival," but it was discontinued in 2003.