Of all the eagerly anticipated phenomena that mark the spiraling dance of the seasons, few are as sweet, or received with such delight, as the appearance of lightning bugs in June.
Perhaps you call them fireflies. I grew up calling them lightning bugs. In fact, they are neither flies nor bugs. They are winged beetles, in the order Coleoptera. And for many of us who grew up the Midwest, these seemingly magical insects provided an early-childhood introduction to the joyful exploration of the natural world. Many of us have fond memories of dashing across the lawn, big glass jar in hand, chasing flickering points of light and squealing with anticipation of the capture. And we always knew that we could catch these harmless little insects in our bare hands, examine them closely—in rapt fascination of their eerie rhythmic glow—keep them for a time in our clear glass jars (breathing holes punched in the metal lids), and release them once more into their habitat before we were tucked into bed.
Adaptation in nature is nothing less than amazing. Why would a little insect evolve in such a way as to regularly emit such a bright, distinctive glow? The short answer is that they use the light to communicate. And most of that communication is about finding a suitable mate.
There are thousands of species of lightning bugs (or fireflies—I’ll use the terms interchangeably) spread across temperate and tropical areas of the globe, classified within five subfamilies. While there are more than 200 species in North America, curiously enough there are few species that occur west of Kansas. (If you really want to impress your friends visiting here from out west, take them to a firefly show.)
Firefly behavior, color, and habitat preferences vary by species, but in general their bioluminescence is caused by enzyme-induced chemical reactions within specialized cells called photocytes. Reflector cells may intensify and direct the light emitted by the photocytes. Light cast by a firefly is extraordinarily efficient; it is what we call a “cold light” because, unlike most sources of illumination, there is no energy lost as heat.
While some fireflies may emit light to defend their territory or deter predators, what we typically see is a courtship display. Each species presents a distinctive blinking pattern that is unique to that species (although there are a few species that mimic one another as a means of interspecies trickery). Males flash their rhythmic signals in flight while females perch in low vegetation; a female may reflect the male’s flash pattern or she may, at a precise time interval, blink back to the male, signaling her whereabouts; the flashing and blinking typically continue until mating is complete.
The female lays her eggs under the surface of the soil. After about three weeks, the eggs hatch, revealing larvae that are fascinating in appearance: segmented and armored, looking perhaps like a trilobite or some kind of spiny pillbug. The larvae persist in that form for a year or two before spending about three weeks as pupae, emerging as adults who then live for only 3 or 4 weeks—just long enough to reproduce.
It is pleasing to find a field or woodland edge filled with the silent twilight courtship display of fireflies. Even as adults we can be mesmerized by the flashing, dancing patterns of green or yellow points of light, swimming in the mild evening air. And yet, some neighborhoods—even some natural areas—seem to host fewer lightning bugs today than in years past. I haven’t found any published studies that compare population trends over time, but there are anecdotal reports of diminishing numbers.
Most of a firefly’s life is spent in larval form, on or below the surface of the soil where they are susceptible to environmental dangers such as drought, flood, contaminants, and predation. Some of the threats to lightning bugs are decidedly human in origin. Lawn chemicals are especially troublesome: some can kill firefly larvae outright, and they might also kill the organisms that the larvae need to eat. Artificial lighting can reduce the ability of adult males and females to find each other, so we are encouraged to shut off our lights whenever they are not needed.
Those of us who grew up in suburban neighborhoods here in the Midwest may associate lightning bugs with lawns and the residential landscape, but of course those little beetles were here long before modern humans changed the environment, so what natural habitats would have been their haunts? Reportedly, they prefer moist environments that support low-stature vegetation. I would suppose that sedge meadows, mesic savannas, and the margins of wet prairies would have been their preferred habitats.
The ideal time to witness the firefly display is right around dusk, a little after sunset, at the onset of darkness. Firefly activity diminishes considerably about an hour or two after sunset.
Take my advice. Find a moist prairie, sedge meadow edge, or untreated old field. (If you live in a neighborhood that still has abundant lightning bugs, you can do this at home, although ambient light from the neighbors can interfere with the experience.) Perch yourself comfortably at sundown, and take in the show. Allow a soft focus to guide your steady gaze across the gloaming space in front of you. Turn off your thoughts for a few moments, quieting the internal dialog; with silent mind and open eyes, witness the play at hand… and smile like a child enchanted.