Revisit this popular story from July 2022, in which Aaron Voogt shines a light on Michigan’s lightning bugs.
It’s a Michigan summer evening, and you’re taking in the twilight hour in your backyard. Crickets chirp in the distance, birds settle into their roosts, and the sun’s glow gives way to darkness. That’s when you see them: a few blinks here and there; the first suitors of the night flashing their tentative greetings. More appear, and soon the grass and trees are dotted with a quiet firework show.
These are, of course, Michigan’s fireflies. Also called lightning bugs, they’re a familiar sight across North America, with a large density of species on the middle and eastern side of the continent.
I remember childhood summer nights spent in awe of their light shows. To this day, I’ll scoop them from the air and watch as they crawl around my hand. Even though they come without fail every summer, the first firefly of the year always seems to take me by surprise. This summer, I set out to learn more.
What is a firefly?
While there are many species of fireflies (all belonging to the insect family Lampyridae), the one most Michiganders see is Photinus pyralis, or the common eastern firefly. It’s a small beetle, with a yellow stripe running between its black wings. Its head is red with a black dot in the center, and two antennae twitch nervously in front. Most notably, the last two segments of a male’s abdomen and one segment in a female’s are pale yellow. This is the firefly’s lantern; its light-emitting organ.
But how does this organ work? How can a tiny creature glow? It’s completely alien, especially compared to the seemingly drab beetles that Michiganders typically see. To find an answer, we have to look at what’s going on inside.
Let there be light.
Bioluminescence (the term for light emission from a living organism) has evolved independently at least 40 times. There’s glowing fish (think of the deep-sea kind), glowing fungus, glowing jellyfish, and glowing squid. During the American Civil War’s Battle of Shiloh, wounded soldiers spoke of soft light that emitted from and seemed to heal their wounds. They dubbed it “Angel’s Glow,” and years later we suspect bioluminescent bacteria! And of course there are fireflies, the familiar, yet equally amazing glowing Michiganders.
The bioluminescence process is mostly the same in all of these cases. A molecule called “luciferine” and the enzyme “luciferase” react with oxygen and the energy molecule adenosine 5′-triphosphate (or ATP for short – remember that from biology class?) in specialized light cells. The energy given off from the chemical reaction is released almost completely as biological light. This efficiency is more important than you think.
A standard lightbulb emits most of its energy as heat, with only a fraction (about 10%) as light. Touch the bulb in your bedside lamp to see what I mean. If the firefly had the same level of heat emission, it would fry itself to a crisp. But the biological process is so efficient, almost no heat is emitted.
Putting on a show.
Chemistry aside, what’s the point of all this? Why glow in the first place? The answer is, again, chemistry – but not the scientific kind. We’re talking about love.
Once a common eastern firefly reaches adulthood, it will never eat again. Its entire life from this point on is dedicated to finding a mate. When the sun is setting and the weather’s warm, the stage is set for romance.
A male firefly will fly close to the ground, in what looks to me to be a slow bumbling flight. As they cruise along, they’ll flash their lanterns. After each flash, they’ll wait a few seconds before flashing again. They’re watching for a response from any female fireflies.
Perched on grass below, interested females will flash a response from their lanterns. The two will flash back and forth, until the male finds her and they can, er… heat things up.
As a parting gift to his mate, the male firefly shares nutrients for the female via his sperm. This added boost of energy helps her produce eggs, which is ultimately the whole goal of the operation.
Fun fact: Flash patterns help researchers (and backyard researchers, ahem) identify species of fireflies.
Glowing up strong.
Most of a firefly’s life is spent as a subterranean larva. Feeding on earthworms and slugs, it grows bigger and bigger as a “glow worm.” That’s right, the larvae share their parents’ luminescence. The babies’ soft glowing light is a warning to predators: “Don’t eat me!” they say. And if the warning is ignored, the predator gets a mouthful of a foul-tasting chemical that a curious bird might come to associate with the glowing worms.
As an adult, Photinus pyralis still deals with predators. One of the most fascinating is, in fact, another firefly. Fireflies in the genus Photuris (irritatingly similar in spelling to Photinus) are known as the “femme fatales” of fireflies.
The females of this group mimic the flashing responses of Photinus females. But when the unsuspecting male comes down to mate, he meets his end. That’s right, these fatales don’t subscribe to the no-eating-after-adulthood rule, and their survival depends on this seductive nighttime snack.
How can you tell the difference between sweet Photinus and salty Photuris? Photuris fireflies are longer (about an inch long), have long, slender legs, and glow more green than the yellow Photinus species.
Catching lightning in a bottle (or jar).
If you’ve ever marveled at the displays these insects put on, maybe you’ve also tried to observe them in a jar. There are many tutorials online, but here’s what I do:
Start where they are. Fireflies are mostly found on open land, like fields or lawns. Lots of artificial light can affect them, so it helps to get out of the city or away from the brighter areas of your yard. They also like moist areas, where females lay their eggs in the ground. Try looking near rivers, ponds, or swamps. Truth be told, fireflies aren’t hard to spot.
Carefully capture them. Some people use a net to catch fireflies. I’ve also heard of others attracting them with a flashlight. I’m sure these are both fine methods (be careful with nets, though, which can injure the delicate insects), but jars are incredibly simple for this task.
Start by looking for the flashing of a firefly, and walk in its direction. Once you’re closer, watch for it to flash again, and try to see where it’s flying. When you’re within reach, stick your hand in front of its flight path, and simply scoop it up. Often, they’ll land right in your hand instinctively. You can catch female fireflies by looking for lights on the ground below, and gently scooping them up. They won’t bite.
Once you’ve captured one, put it into a mason jar with holes poked in its lid (make sure you already have this with you, or else you’ll have to shuffle with cupped hands back to the house). Once you have a few in the jar, carry them to a dark place to watch them glow. Each firefly only flashes every few seconds, so be patient. Shaking them or tapping on the jar will only delay their lights, and it’s rude. Sit back and enjoy the chance to observe them so closely.
I like to let my fireflies go the same night I catch them. That way, they can get back to their mating. I promise that it’s just as enthralling to watch them fly off into the night, flashing a little goodbye.
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