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How do Fireflies Glow?

Mary McMahon
Updated Jun 04, 2024
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Fireflies produce biolumiscence through a chemical reaction, using specialized enzymes produced by the cells in their tails. The resulting light is sometimes called “cold light,” since it generates no infrared or ultraviolet rays. The mechanics of this biological feat are well understood, although the reasons are a bit more murky. The light appears to serve a range of purposes, from attracting prey to signaling potential mates.

Before delving into the details of how fireflies produce light, it may help to know what this insect actually is. Technically, they are beetles, not flies, and there are over 2,000 species in the order Lampyridae that are capable of producing light. The ubiquitous insects can be found in warm and temperate climates all over the world, and they may also be called lightning bugs or lightning worms. In some cultures, their appearance is an exciting event, and people may hold festivals to celebrate their emergence, since it often marks the start of summer.

The main chemical involved in generating their light is luciferase, an enzyme that interacts with oxygen to glow. The special enzyme is produced by the cells in the insect's tail, and they rely on a chemical called ATP to stimulate production of this enzyme. ATP regulates cell processes in all living organisms, and it serves a wide range of functions related to cell function.

Many people have noticed that some fireflies flash on and off. These flashes are actually used as signals to communicate with other bugs. Some species can mimic the signals of other species so that they can attract a source of food. The glowing light also warns predators, as luciferase does not taste very pleasant, so other animals quickly learn to avoid glowing insects, no matter how appealing they might look.

Most fireflies are nocturnal, and they often come out around dusk in a spectacular show of lights. Other species are diurnal, and some beetles in this family cannot produce light because they have adapted for life during the day. In regions with a large firefly population, some people greatly enjoy wandering around in marshes and woods as dusk, when they come out in large masses. Lightning bugs are also common features in novels about the Southern United States, where the insects can be found in large numbers on languid summer nights.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a All Things Nature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments
By StarJo — On Aug 22, 2012

My grandfather used to say that fireflies would fly so high in the sky that they could capture the light from the sun in their bodies. He said that they gathered enough light to last through the entire night.

My sisters and I believed him for a long time. Our biology teacher finally ruined this story for us with the truth. Still, we thought it was really poetic, and we were grateful to him imparting this bit of his imagination to us.

By giddion — On Aug 21, 2012

It is really neat to watch for the first firefly of the evening. My cousins and I used to do this in the summer as kids, and we made a contest out of it.

I remember feeling the anticipation as we all sat on the porch, staring out into the woods across the way. The first one to yell out, “Firefly!” when we saw the first light of the night would win.

Even now, I catch myself staring into the distance at dusk, hoping for the first sign of summer. To me, the true transition from spring to summer is marked by the first firefly.

By JackWhack — On Aug 20, 2012

@LisaLou – Glow worms aren't actually the same thing. They don't fly. They look like actual worms, and they hang out in the grass and in caves.

I saw some in the grass one night while I was out in the swimming pool. At first, I thought that they were lightning bugs that had landed on blades of grass, but upon closer inspection, I could see that they were actual glowing worms!

By fify — On Aug 20, 2012

@turkay1-- That's true but oxygen isn't the only factor that affects how and for how long fireflies glow.

Like the article mentioned, it also has to do with the species and mating. We tend to think of fireflies as one group of beetles. But there are many different types and each type has their own patter of flashing. They use this pattern to identify other fireflies in their group to mate. They want to make sure that they don't mate with the wrong firefly!

I've also heard that the stronger the flash and the more rapid it is, the more attractive the firefly is to potential mates.

By candyquilt — On Aug 20, 2012

@feruze-- Do you know why fireflies glow periodically?

It's because they have an organ that's in charge of light production and it can only produce the light when it has oxygen. So when the oxygen is transported into the organ, the light is produced. When the oxygen runs out, the glowing stops.

That's why fireflies constantly light up and then light off. They're waiting for more oxygen to come through.

Isn't that cool?

By bear78 — On Aug 19, 2012

@anon144095-- Do you mean that they only light up when they're flying up?

No, I've never noticed that. I always thought that they just light up periodically, regardless of whether they're still or moving. I usually see them light up every few seconds or so and they continue to glow for a few seconds at a time too.

I love fireflies. I grew up in Ohio and we used to get lots of them at dusk in the summer. I never knew until now how they produce light, but I think these are some of the most spectacular bugs ever. I've always likened their glowing part to a light bulb! I would love to see other types of fireflies and glowing bugs too.

By LisaLou — On Aug 18, 2012
I have always used the term lightning bugs and fireflies interchangeably. I have never heard them called lightning worms though.

I wonder where this came from, as they look nothing like a worm at all.

By honeybees — On Aug 18, 2012

I have a friend who grew up in Montana, and she was an adult before she had ever seen any fireflies. She wasn't fascinated by them, she was scared to death of them.

Her husband tried to catch a few of them and show them to her up close, but that even made it worse. She is a little bit more used to seeing them now, but I don't think she will ever be comfortable with them.

By julies — On Aug 18, 2012

I also grew up with fireflies and spent hours trying to catch them on a summer evening. Some people might be put off by this, but we would remove the light from their body and wear it as a ring on our finger.

It would continue to glow for awhile and we thought this was pretty cool. They do have an odd smell to them though, and I can see why certain predators would stay away from them.

By golf07 — On Aug 17, 2012

I live in the Midwest where we have a lot of lightning bugs. Every year I am so excited when I see the first sign of them because I know that summer is finally here.

There is something very peaceful about sitting outside on the deck on a hot summer evening and watching the fireflies dancing around the yard. I have always been fascinated by their glow.

When we were kids we would catch them and put them in a jar so we could watch them light up our bedroom at night.

By anon144095 — On Jan 18, 2011

Has anyone ever noticed that they seem to only illuminate during ascent? Wondering if this is true and if there is a reason. thanks.

By anon113602 — On Sep 25, 2010

You mentioned they don't taste good so predators avoid eating them. My three year old grandson would probably take issue with that. He ate a handful of them!

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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