Why Fireflies Light Up at Night

Even if you’re the sworn enemy of all things bug, you have to have a soft spot for fireflies. They’re harmless, pretty, and they remind you of summer. What’s not to like? When you think about it, though, aren’t fireflies a little… weird? If you’ve read any of our other bug-based blogs, you know that nothing in the bug world happens without a reason. But what reason could fireflies possibly have for lighting up at night? It doesn’t seem like a great way to stay alive, certainly. Come to think of it: how do they light up at night? If you’ve ever watched fireflies twinkling in the distance on a calm summer’s night and thought, “hey, wait, why are they doing that?”, this blog’s for you.

How It Works

The process by which fireflies create light is called “bioluminescence”. Fireflies control bioluminescence through a fairly complex chemical reaction inside their bodies. First, they process food and break it down into the chemicals required to start the process, which include calcium and the energy transporter Adenosine triphosphate (ATP). These chemicals react with a compound fireflies naturally synthesize in the cells of their abdomens, called luciferin, to create an enzyme called luciferase. Luciferase combines with oxygen and ATP to generate light. When oxygen enters the firefly’s light-producing organ, it combines with the other chemicals in the organ rapidly, creating excess energy that’s disposed of in the form of light. Fireflies are capable of regulating when they allow oxygen to enter their light organs by “opening up” or closing the organ at will. When the organ is open, oxygen enters and the firefly glows. When they close the organ, oxygen can’t combine with luciferase, and the lights go out. Different species of firefly may even glow in different colors, including the traditional yellow, light blue, or even faint red.

Why They Do It

Fireflies light up for a wide variety of reasons. Different species have different flash patterns, which they produce by opening and closing their light organs in specific sequences. Fireflies have been observed using these flash patterns to communicate with one another. They use call-and-response flash patterns to indicate which type of firefly they are, whether they’re friend or foe, and more. Fireflies even use their glows in mating. Female fireflies choose mates based on how much they like the way a suitor glows. Higher flash rate and intensity are considered very attractive. Impressed females flash back at performing males to indicate interest. Males should beware, however. Sometimes a flashing female could be interested in something other than mating. Some females can imitate the flashes of other firefly species. When the would-be casanova gets close, the firefly femme fatale earns an easy meal!

When They Do It

Fireflies spend winter burrowed underground as larvae. Like many other bugs, fireflies are cold-blooded. They need to be in hot and humid places to warm up and survive. The heat and humidity of their environment largely determines how long it takes for fireflies to complete their life cycle from egg to adult. The faster eggs hatch and larvae grow, the more adults will be around to light up your summer. During particularly warm or wet springs, fireflies mature quickly. You might even see them as early as April or May. You may also see more fireflies after a mild winter, because more larvae managed to survive. If the weather gets too dry, however, firefly eggs and larvae may die before maturing. Adults will take longer to emerge, and they’ll appear less frequently. When fireflies finally reach adulthood, they’re pretty much all about mating. Firefly population usually peaks around mid-to-late summer. If you want to see the light show, your best bet is late July to early August.

Where You Can See It

All fireflies are cold-blooded and need hot, humid environments. Some are even aquatic or semi-aquatic, and lay eggs on the surface of standing water. Like most bugs, fireflies prefer to live near a source of water. Most fireflies are nocturnal and spend days sheltering in shade where they won’t heat up too much, so they also like to live in areas with tall vegetation like grass and stalks. Ponds, swamps, and marshes check off each of a fireflies “ideal home” requirements quite conveniently. The best way to spot fireflies is to wait until after dark and then head out to the nearest brackish pond or marsh. Look out over the water, especially near cattails and other high vegetation. If you’re having trouble seeing them, try looking lower; most fireflies skirt the surface of standing water by only a few inches. Watch for fast blinking patterns to figure out which flies are in a mating mood! Fireflies are beautiful, mysterious creatures… but they probably don’t change your opinion on the whole bug kingdom very much at all. Sure, fireflies are cool, but the rest? Ehhh… So if you’ve got a bug problem that’s not exactly filling you with wonder at the beauty and mystery of the natural world, let us know. Plunkett’s has the knowledge and experience required to put an end to any kind of pest problem, so you can get back to enjoying your summer. Happy firefly hunting!

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