The Rainy Day Naturalist: Lightning Bugs

I would like to go for a ride with you, have you take me to stand before a river in the dark where hundreds of lightning bugs clink this code in sequence: right here, nowhere else! Right now, never again!

Amy Hempel

Lightning bugs flash in the warm dark of a summer evening—icons of the season. While we humans may romanticize the scene, it really is all about romance for the lightning bugs. In most species the males fly to flash their evening signals of availability—sort of saying: “Hey, baby . . . I’m a stud . . .Hey, baby . . .” with light instead of words. Perched on foliage below, interested females then give them the green light—which may also flash yellow or amber depending on the species.

Most types of lightning bugs do not have common names, but the one you’re most likely to see after dusk in northeast Indiana is dubbed the Big Dipper (Photinus pyralis). In June and July their yellow, one-second flashes advertise romantic rendezvous. Their leisurely flying speed lures children to chase and catch them. Another Indiana lightning bug, Say’s Firefly, is the state insect. It was named for Thomas Say, a Hoosier entomologist, who first described the species in 1826.

That ability to create a flash of light sets lightning bugs apart from most other insects—and other species. How do they do it? In short, it’s oxidation. However, it’s not burning oxidation like in a camp fire. Rather, this oxidation takes place more gently in a process called bioluminescence, a reaction between the chemical luciferin and the enzyme luciferase, that releases a photon of light but little heat.

Worldwide there are about two thousand different species of lightning bugs—members of the insect family Lampyridae. One hundred seventy species are found in the United States, and Indiana is home to about forty-three. While the lightning bugs we see flash randomly, some varieties in the tropics can synchronize their flashes. Imagine what it would look like to have a tree full of lightning bugs all pulsing to the same beat.

Not all lightning bugs actually light up. Only about three-quarters of the species in Indiana can flash. They are all beneficial, however. In their larval form, they improve the soil by burrowing. They also eat other harmful insects, slugs, and other pests.

How about a little confusion? There are “dark” lightning bugs that don’t flash. Plus, lightning bugs aren’t really bugs at all. Do you call them fireflies? Even though they fly, they are not flies either. The (mostly) luminescent members of the Lampyridae family are all types of soft-bodied beetles. Like other beetles, lightning bugs have two sets of wings. Their outer wings are harder and make a shell to cover the folded, longer wings the insects actually use to fly.

So should we call this luminescent beetle a lightning bug or a firefly? Or maybe you’ve heard them called names like firebobs, candleflies, and firebugs? These names are examples of regional dialects—like whether you call a carbonated soft drink soda or pop. The name lightning bug is more commonly used in the Midwest and South while fireflies tend to live on the coasts. Whatever you call them, they are a delightful addition to Clear Lake’s soft summer nights.

The difference between the almost right word and the right word is really a large matter. 'tis the difference between the lightning bug and the lightning.

Mark Twain