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The spellbinding, though misnamed, lightning bug
is much more than just a pretty light show.
When it comes to childhood high-summer fun, catching lightning bugs may occupy the nostalgic pinnacle—even above chasing the ice cream truck and running through the sprinkler. Fireflies turn an ordinary backyard into a fairyland. On the stillest, most satisfying evenings, when the grass is mown and the bicycles have been put away or when the tent has been pitched and the marshmallows are melding the s’mores, even adults can be caught in their spell.
Lightning bugs hold such a place of enchantment in our hearts that we don’t think of them as having a normal insect role in lawn and garden ecology. But “they’re highly beneficial, especially if you have slug or snail problems,” says Daniel Frank, an entomologist with the West Virginia University Extension Service. That is, these creatures of magic are also predators. “The larval stage feeds on various invertebrates in and on the soil—that includes snails and slugs—and they can attack other pest insects, too.”
Like a lot of us, though, lightning bugs lavish their most spectacular behaviors on courtship. What for us is a charming phase of the warmer months is, for lightning bugs, mating season.
Making Light
Before we talk about insect flirtation, it’s useful to understand that what we call lightning bugs or fireflies are actually neither bugs nor flies. A truer term for them might be “lantern beetles.” Their young, sometimes called glowworms, should really be called “glow larvae.”
All fireflies belong to the family of beetles known as Lampyridae, from the Greek word for “shining.” Lampyrids encompass 110 genera and thousands of species worldwide. In West Virginia, we have at least six genera and 13 species—that’s what’s represented so far in the state Department of Agriculture’s quarter-million-specimen insect collection in Charleston, according to Taxonomic Entomologist and collection Curator Laura Miller. “There could be more,” she says.
Fireflies are masters of biochemistry. Like many other creatures that glow, they make their light by combining a compound called a luciferin with the enzyme luciferase—both named from Latin “lux,” for “light.” “When luciferin and luciferase come together in the presence of oxygen, they make a flash,” Frank says. It’s one kind of bioluminescence. “Some call it a ‘cold light’ because it really doesn’t release heat like an incandescent bulb does,” he says. “It’s pretty much 100 percent efficient.”
If you’ve never seen a glowworm, they’re not too hard to find once you know the firefly life cycle. Like all beetles, fireflies go through a complete metamorphosis, with a cycle of four stages: egg, larva, pupa, adult.
Females lay their eggs in places where the soil is moist, and eggs take a few weeks to hatch. “They generally live for about a year, in most species. They spend the immature, larval stage overwintering in the soil,” Frank says. These are the glowworms. In fall and spring, they can sometimes be found glowing at the soil under leaf litter, where they hunt small prey.
After the winter, “they pupate in the soil and then emerge as adults, usually in late spring or early summer,” Frank says. “If we have a really warm spring, you’d see emergence earlier. Then they’ll typically be out and about until around July—or, if we have moist, humid weather all summer, that could expand how late we see them, maybe even into the fall.”
By “out and about,” he means advertising for love.
Love Languages
The typical lightning bug courtship goes like this: Males fly around, flashing ardently. Interested females, perched on vegetation, respond with single flashes. Males approach females, and consummation ensues.
Even the broadest lines of that interaction—males in the air, females stationary—are lost on us humans. Yet there’s so much more nuance to it than that—for example, color. That’s how taxonomist Miller organizes lightning bugs for people who aren’t insect scientists. “I have listed them by their light-producing colors,” she writes in an email detailing her West Virginia collection’s Lampyrids. Their luminescences fall into three main color categories.
Most of the firefly lanterns we see give off the familiar light yellow-to-green glow. That’s usually Photinus pyralis, the Common Eastern Firefly that’s pretty ubiquitous across the eastern U.S. It could also be its close relatives, four or more other species of Photinus that live here in the state. They’re the iconic half-inch-or-so-long lightning bug.
Look closer: Do you notice an amber tint? That’s not necessarily a mutant. It could be one of West Virginia’s Pyractomena species. Also about a half-inch long but darker-winged, they’re found in wetter areas and their larvae feed on aquatic snails. Or is your flasher more of a dark green? That could be the cannibalistic Photuris—more on that below. They range larger, from half an inch to almost an inch in length.
Timing, in Romance, is Everything
But lantern color isn’t the only way to distinguish one type of lightning bug from another. “Species can also be separated or identified in the field by the number, duration, and frequency of their flashes,” Miller says. The differences can be minute, but some flash patterns are easy to pick out.
The common Photinus pyralis is fairly easily identified by its distinctive J-shaped flash pattern. The male Photinus consanguineus has been documented with a double flash. If you see rapid flashes—four or more in the space of a second—you’re probably looking at Pyractomena angulata or Pyractomena dispersa. By having a unique flash pattern, each species can find its proper mate in the low light of dusk.
Seeking intimacy in the dark can be dangerous, though. The female Photuris, the cannibal mentioned above, mimics the flash response a hovering male Photinus is looking for. When he lands, she injects him with her digestive venom and eats him. Photuris isn’t looking for love. She’s after defensive compounds in Photinus’s blood that make it unpalatable to spiders and other predators. Photuris acquires the protection for herself and also passes it on to her eggs. The Photuris female is, in the words of Tufts University biologist Sara Lewis, “a firefly vampire brought to you by natural selection.”
Documenting and Protecting
Firefly behaviors beyond outrageous conduct haven’t been thoroughly documented. While they can vary a lot—the insects flash more slowly at higher temperatures, for example, and they may be affected by wind speed or pollution or factors we’re not even aware of—harmless insects don’t attract the level of scientific resources the pests we need to control do.
But some firefly behaviors are perfect subjects for citizen-scientist observations, along the lines of Audubon Society bird counts. Firefly Watch, an online project of the Boston Museum of Science, has logged data from thousands of observers across North America since 2008. In West Virginia, participants have noted single, double, triple, quadruple, and flickering flash patterns as early as April 25 and as late as October 9, under very specifically documented conditions of habitat and weather.
Some ecologists believe there’s been a decline in the numbers of lightning bugs in recent decades. If that’s true—it’s hard to be sure because documentation is so incomplete—entomologists see several possible causes. “Habitat loss will cause problems,” Frank says. “If you’re covering land with concrete or converting land to industrial agriculture, that takes away habitat they would use—they like wooded areas and fencerows. And if you’re disturbing the soil, you don’t have that habitat the larvae need to survive.” Pesticides and artificial light may contribute, too. “Light pollution has become a problem for a number of insects,” Frank says. Simple steps like reducing the amount of light we use outside our houses in the evening and avoiding harsh lawn and garden chemicals may help.
Do we really need fireflies? Biologist Lewis asked and answered this question in “The Loves and Lies of Fireflies,” her popular TED talk: “Every time a species is lost, it’s like extinguishing a room full of candles one by one,” she said. “You might not notice when the first few flames flicker out—but in the end, you’re left sitting in darkness.”
This story was originally published in the July 2017 issue of Wonderful West Virginia magazine. To subscribe, visit wonderfulwv.com.
written by Pam Kasey
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