The Most Spectacular Firefly

And God said, "Let there be lights in the vault of the sky to separate the day from the night, and let them serve as signs to mark sacred times, and days and years, and let them be lights in the vault of the sky to give light on the earth." And it was so. (Gen. 1:14–15, NIV)

Light has a way of marking things. Fireflies, though not grand light sources like the moon or Venus, nevertheless illuminate warm evenings with their delicate glow. When I saw them as child, I knew that green summer had begun and it seemed endless to my small self. The golden light of fireflies meant more daylight to stay up late, watermelon in the backyard, and more frequent visits from my grandmother. These living lights, suspended like low-hanging constellations, were signs that marked my seasons and days and years.

Fireflies still signal summer in my internal calendar, though summer seems much briefer to me now. I see them blinking and hovering near the hydrangeas, and wonder about a God who made an outwardly plain bug with this extravagant ability. The scientific name for this is bioluminescence—the ability of a living thing to produce light. It is something that has captivated us humans for millennia. In our current world riddled with manmade lights that fill even the palms of our hands, these creatures that generate their own light in darkest nights or deepest oceans betray a genius far greater than our own.

In her new book, Silent Sparks, ecologist Sara Lewis describes the astonishing intricacies of firefly physiology and behavior. Biologists have discovered that light from these glowing creatures is made by a specific enzyme known as luciferase (from the Latin word lucifer, which means "bringer of light"). Luciferase and a few other key ingredients allow fireflies and their supine siblings, glow-worms, to have the ability to light up the night. Their lights serve a two-fold purpose: a warning to would-be predators to steer clear, and a luminous mating display.

The fireflies that most of us see hovering just above the ground are overwhelmingly male. The males of each species have a set pattern of flashes that vary in number and duration. Each summer evening, we are witnessing them woo the females, who spend most of their lives on blades of grass or low-hanging shrubs. And while it is amazing to see fireflies display their lanterns on any evening, there is one species out of over 120 in North America that is even more wondrous than the rest: Photinus carolinus.

Photinus carolinus is known as a synchronous firefly. Found in the Great Smoky Mountains National Park, these gather under the trees as night falls and begin flashing their lights in unison. Observers talk about waves of light filling the age-old forest and then darkness obscuring everything for a moment. And then it begins again—a sort of ordering of light in the midst of the darkness. No one can explain exactly why Photinus carolinus does this. Lewis and her colleagues have studied them extensively, and while the flashing is still part of their mating ritual, no one is sure why these particular fireflies decided to make it a group effort.

My husband and I are regular visitors to the park. It is an otherworldly place and feels much older than the surrounding terrain. The mountains have rounded peaks that look like the knuckles of a giant hand resting on the earth, and fog fills the valleys every morning, making an ocean of white surrounding the green peaks. It is a place where we've encountered families of black bears foraging in the forest, and families of locals who tell us where the best hidden waterfalls are located. So when we first heard of the synchronous fireflies a few years ago, we determined that we had to see them. This is how we found ourselves stumbling through the branch-filled darkness waiting for what I still did not believe would happen.

We set up our viewing area well before nightfall. Photinus carolinus occurs in a very small area of the park that was once a community of cabins known as Elkmont. It is obvious from their remains that the homes were well-loved, but now the forest is reclaiming them. New saplings of maple and tulip poplar are springing up in side yards and sidewalks, while Virginia creeper and maidenhair ferns take root in rock wall crevices. The area is bordered by the Little River, which hides brook trout and salamanders as its water slips over spotted stones in sheets and eddies. As I watched the light dim, a great blue heron winged silently by, headed upriver. Even if we didn't encounter the fireflies, it would have been enough.

I never realized how dark the night could be. There are no lights in park, and no cell phone service. Regular flashlights or any sort of light pollution will disrupt the firefly signals (and your own night-adjusted vision), so only red-filtered lights are allowed. We had as our one source of illumination the red light of my husband's headlamp. Without that I could not see my hand in front of my face. However, the beauty of such profound darkness is that even the smallest light becomes miraculous.

When the darkness was complete, I began to see fireflies—only one at first, and then a few others. They seemed larger than any I had encountered before, but there was no synchrony. We waited and watched. It was beautiful, but not synchronous. I wondered if we were too early in the season for Photinus carolinus. We turned back from the river and tried to make our way to road, holding onto each other and trying to dodge tree limbs. As we entered the prickly darkness of the woods, it happened.

One low-lying firefly sparked green on the edge of the forest, then dozens more answered, telegraphing their light like stars in a newborn galaxy on the forest floor. Then the darkness enveloped us again—for only a moment. The fireflies orchestrated their tide of light a few times every minute it seemed. At times it seemed to slow, then grew more frenetic. The fireflies occasionally flew high in the trees, descending like tiny spotlights near our shoulders and heads, or hovered so close we thought one would land on us. Again and again a cool glow washed over the ancient forest, and it was marvelous to behold.

As we kept silently watching, we realized that we were present with over a hundred other souls who had gathered to watch as well. Most were speaking in hushed tones, and many in foreign languages. It seemed that Photinus carolinus, a smallish member of the beetle family, had captivated people all over the world. Perhaps that was the other wonder of the night: that even in a distraction-filled, convenience-obsessed culture, there are still people who will make a pilgrimage into the darkness to see these tiny light-filled creatures. Light has a way of marking things.

Julie Sumner is The Behemoth’s poetry editor.

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