Peering through the dark from the front porch, the flashing lights catch my eye. Floating just a few feet above the ground, their glowing sequence could send the imagination flying into thoughts of fairies and other supernatural beings. But the lights were neither supernatural nor human-made.
Nothing reminds me of my childhood more than seeing lightning bugs. I would chase them with an empty jar, popping them in whenever I managed to catch one, and peering at them for what seemed like minutes but was more likely hours before releasing them unharmed. Even with television, and before video games, we had the bioluminescent entertainment of insects to occupy our time—and we still do, if we just let them.
It was only much later in life that I realized that they weren’t bugs at all. Their official common name is fireflies, but they aren’t flies either. They are actually beetles, within the family Lampyridae, which denotes species that shine like a lamp.
There are about 2000 species of fireflies world wide, but only 15 reside in Kentucky. They range in size from 2/10 of an inch to full inch long, and most but not all generate light.
Fireflies spend most of the summer searching for a mate, which is the primary reason that they light up. Each flash is a firefly saying, “I’m here!” in an attempt to attract the opposite sex. Both sexes flash their lights, but females typically remain in one place, flashing only when they notice an impressive male. Each species has its own unique flashing pattern. Once mated, the females lay their eggs and die. The next generation emerges the following spring and the cycle begins again.
Fireflies sometimes use their flashes for more than mates. Some species use it to repel predators or attract prey. Fireflies taste bitter, so predators learn that if it lights up, it tastes bad. Some females will mimic the flashes of females from other species to attract males of these species, which they then consume. Males cannot always assume that females are providing honest signals about mating—they might be waiting to eat them.
Fireflies use bioluminescence, a term that describes how living things create light. Fireflies have light organs that contain luciferase, a chemical that when combined with other substances, produces a light that is perhaps the most efficient on Earth. Scientists estimate that almost 100 percent of the energy in the chemical reaction is emitted as light; in comparison, an incandescent bulb only emits 10 percent of its energy as light, and even the best LED bulbs are 80% efficient. Perhaps someday firefly tech will allow us to improve our lighting efficiency even further. Other research has discovered new uses for luciferase, including detecting blood clots, evaluating cancer medications and food safety testing.
Some fireflies, most famously in Southeast Asia, will synchronize their flashes. In the U.S., this phenomenon is commonly seen in the Great Smoky Mountains, but I have seen it myself in west Tennessee. It is unclear exactly why some species synchronize, but it may be a way of males joining forces to attract females or a competition among males to be the first flash.
I’ve observed fewer and fewer fireflies over the years, and others have noticed the same thing. Fireflies are affected by light pollution, pesticides and habitat loss. Humans use a lot more chemicals than they used to, and some of these have likely led to declines. Other studies suggest that fireflies are very site-specific, so when a forest is developed into a parking lot, they don’t move to other areas; they just die off.
We all need fireflies to light up our summer nights, and fireflies have already given us numerous benefits through their bioluminescent chemicals. But as they flash less and less in our backyards, they are also warning us that our actions have consequences. If we don’t protect the environment, we will continue to lose species. Yet many of these species play important roles within the ecosystem that provides us with clean air and water, among other things. If we destroy the pieces of the machine, at some point the machine will break. Like other indicator species, firefly flashes are sending us a message that goes far beyond their search for mates or food.
Even if we cannot enjoy the fireworks this July 4th the way we have in the past, nature has provided some for us. Find a dark corner of your yard, or a woodlot, or visit one of the many regional public lands, and enjoy the spectacular, free show. There are many ways to celebrate our independence, and although firefly displays may not be as noisy or bright as fireworks, I’ll watch them each and every time I can.