Creature Feature: Synchronous Fireflies Work Their Magic at Great Smoky

Synchronous fireflies, showing dorsal view (left) and ventral view (right). NPS photo

What some call the planet’s most beautiful mating ritual takes place at Great Smoky Mountains National Park in June when synchronous fireflies do their thing.

The flying insects that most of us call lightning bugs are winged beetles that are more properly termed fireflies. Whether you call this light-emitting insect a lightning bug, a firefly, or a whatever, it is a member of the Lampyridae family in the beetle order Coleoptera.

Scientific terminology aside, people have two paramount questions about fireflies. How do they manage to glow? Why do they do it?

The short answers: The lower abdomen of a firefly has special organs equipped with chemicals that combine to produce “cold light” through a process called bioluminescence. The flashing lights help fireflies identify and evaluate potential mates. As a rule, males flash and fly while females flash and stay put.

Generalizing about fireflies is a tricky business. Each of the approximately 2,000 species of fireflies found in various tropical, subtropical, and temperate countries around the world has some unique characteristics, and many different species may inhabit a fairly small area. There are at least 200 species of fireflies in North America, and there can be a dozen or more species in a relatively small area that has diversified habitats, too. Great Smoky Mountains National Park, for example, has at least 14 species of fireflies.

Most firefly species are carnivorous, with their larvae subsisting on other larvae, snails, slugs, and similar fare for up to two years before transitioning to the short-lived adult phase (adults survive for only about three weeks). Some species subsist on pollen or nectar.

Adults of nearly all firefly species produce light, although most species that are diurnal (day-flying) produce light only in the larval or glowworm stage. Some give off a steady bluish-green glow, others produce a series of bright yellow Morse Code-like blinks, and still others create a tiny, double-blink beacon. The flashes of some species are pale red, and a few species don’t flash at all.

Since each firefly species has its own flash pattern, there are hundreds and hundreds of variants, some of them unique to small areas. Of all the flash patterns, none is more intriguing than that of the synchronous firefly (Photinus carolinus). Many who have seen synchronized bioluminescence say there is something magical about it – that it surely must be one of the most beautiful mating rituals on planet Earth.

Synchronized flashing is pulse-like, appearing as a brief burst of light from myriad sources followed abruptly by darkness. Scientists still haven’t come up with a generally accepted explanation for the synchronized flashing, but most hypotheses lean to the idea that it increases the likelihood that females will notice the flashing and be able to evaluate potential mates.

Despite what their name implies, synchronous fireflies don’t always flash in unison. Sometimes they produce sequential flashing patterns that seem to move across the landscape in a rippling or wave-like manner. Some of the time there is no pattern at all.

Synchronous fireflies perform their magic in certain parts of Southeast Asia, but you need not travel that far. You can see this amazing phenomenon in the Southern Appalachians each spring, and the best place to do it is in Great Smoky Mountains National Park.

Visitors have seen synchronous fireflies at work in various areas of the park in recent years, including the Elkmont, Sugarlands, Cades Cove, Hot Springs, and Greenbrier vicinities as well as the Joyce Kilmer-Slickrock Wilderness Area.

The Elkmont campground/trailhead area, which is conveniently situated a few miles southwest of the Sugarlands visitor center, is an especially popular place for firefly viewing. In fact, if you plan to spend an evening there during the peak flashing season (early- to mid-June), you can expect to have plenty of company.

Because the only access to Elkmont is a spur off Laurel Creek Road, the heavily-traveled route between Sugarlands and Cades Cove, traffic congestion poses potentially serious problems. To help keep these problems to a minimum, the NPS closes the Elkmont spur (except to registered campers) during the peak firefly season and also provides a trolley service that takes visitors from the Sugarlands Visitor Center to Elkmont and back.

This year the trolleys will run June 7-14 from 6:00 p.m. to 9:00 p.m. (or until the Sugarlands parking lot fills up). The last trolley leaves Elkmont at 11:00 p.m.

If you want to make plans for firefly watching at Great Smoky, you can find additional relevant information at this site. Inclement weather is a potential spoiler, so keep a weather eye out. For up-to-date information you can call the park at 865-436-1200.

Postscript: Sadly, the synchronous fireflies in Southeast Asia are not doing so well, and humans are mostly to blame. Woodcutting and related activities have destroyed or severely altered much of their preferred habitat. In many areas, light pollution obscures flashing and makes it difficult for fireflies to locate mates.