Why Do Fireflies Glow And Other Illuminating Facts

Check out these "illuminating" facts about these fascinating insects.

Many backyards are already aglow with magical fireflies—or lightning bugs as many people call them. On warm evenings, there’s nothing better than sitting and watching them light up the night. Here are a few fascinating facts about fireflies you may not know.

10 Fascinating Facts About Fireflies

  1. It turns out that it’s not just the adult firefly that lights up. Among some species, the eggs glow, and the eggs of certain species will flash if you tap them gently. Most larva – often called glowworms – are also capable of producing light.
  2. They’re energy efficient. No man-made light source can claim to be entirely energy efficient, but a firefly’s glowing tail uses 100% of the energy it produces to emit light. By comparison, the average incandescent lightbulb releases 90% of its energy as heat and 10% as light, while fluorescent bulbs release 30% as heat and 70% as light.
  3. The flashing is more than just a pretty light show. Among the species of fireflies that produce a glow, each one has its own unique flash pattern, and they use the flashes to attract mates. Females wait in tall foliage, flashing to attract males. The males flash in response as they move closer to the females. The glow is also a handy way to repel predators. Since fireflies produce bitter chemicals as a response to predators, most insect-eating animals know that if it lights up, it tastes bad.
  4. It’s easy to identify fireflies by their flash patterns. Photinus pyralis is one of the more common types found in the United States, and this species always makes a J-shaped flash by lighting up as they fly in an arc. Photinus brimley flies in a straight line and produces one flash every three to eight seconds. Photinus consimilis makes a double flash every five seconds, and Photinus collustrans flashes three times in two to three seconds.
  5. Some fireflies are tricksters. While adults of most species eat pollen or smaller insects, some females of the Photuris genus prey on male lightning bugs of other species. They’ll lure the males in by mimicking their flash patterns. And, since female Photuris fireflies gravitate towards the flash patterns of different species, male Photuris fireflies mimic those species to attract the females.
  6. Not all fireflies make yellow or green light. Pyractomena lightning bugs, for instance, create orange light. In the southern United States, you may chance across Phausis reticulata, or the Blue Ghost lightning bug. Blue Ghosts don’t flash at all, instead, they produce a soft but steady blue glow. Others, particularly those that live in the western United States, don’t light up at all.
  7. Some fireflies can actually synchronize their flashes. In the United States, there is only one synchronous species – Photinus carolinus—and there are only a few spots to watch as they put on one of nature’s greatest light shows. You can catch a glimpse in the Allegheny National Forest in Pennsylvania or the Congaree National Park in South Carolina. The best place to watch, however, is the Great Smoky Mountains National Park in Tennessee. People flock to this park every May and June to watch as thousands of lightning bugs produce perfectly timed flashes.
  8. Lightning bugs glow because their tails contain just the right chemicals and enzymes (calcium, adenosine triphosphate, luciferin, and luciferase) to create a bioluminescent chemical reaction. These insects control the flashing by adding oxygen to start the chemical reaction within the light-producing organ in their tails.
  9. They help save lives. Researchers have discovered that the luciferase produced by fireflies is useful for anything from detecting blood clots to tracking the efficacy of cancer medications. In fact, scientists have learned how to make synthetic luciferase, which means that the medical industry no longer needs to harvest this bioluminescent chemical from them.
  10. They have surprisingly short life spans – only one season. They spend most of their adult lives searching for a mate. Once mated, the females lay their eggs and die shortly thereafter. New crops hatch the following spring and the cycle starts over!

Read: Are fireflies disappearing?

Watch this footage of the Tennessee Fireflies lighting up the sky in the Great Smoky Mountains:

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Amber Kanuckel

Amber Kanuckel is a freelance writer from rural Ohio who loves all things outdoors. She specializes in home, garden, environmental, and green living topics.

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This is the first year I have seen fireflies in my back yard and they flash orange! It’s nice to see them again! I’ve been here since 2003!

Maria Elisabete Wyatt

I spy a lighning bug 2021 interlachen fl. April 14th

Barbara Mastrilli

I have enjoyed 31 summers of lighting bugs all thru an over 200 yr old oak in my front yard & pasture. Watching my kids & now grand kids catch & release them.


I have noticed that the fire flies have declined a bunch this year. It might because of all the rain and cool tempatures this spring. I really miss them.

John Pyles

I live in luray va. I have been watching the lighting bugs for the last few weeks, and I noticed that they come up from the ground, and go straight up in the trees and stay there all night, not very many flying around, but the trees are pretty, looks like Xmas lites, does anyone know why ,they mostly stay in the tree

Maria Elisabete Wyatt

Mating and laying eggs


I have seen synchronous firefly displays in northern Ohio.


I have seen fireflies (or as we Kansan’s call them lightning bugs) every evening for the last few weeks. Coincidentally it has been very humid here, a wet spring to say the least. So I was wondering, do fireflies become active as the rain moves through the area? Or is it just a coincidence? Either way I’ve been chasing them around for over 50 years and now I watch my grand kids as they experience the great lightning bug chase in the dark.

Steve Whitehouse

You look tasty x

Mike Madden

All us normal people call them lightning bugs. Only geeks call them fireflies.


I enjoyed reading this article and I was excited to see the video of all the lightning bugs, as we called them. I still sometimes see lightning bugs but there doesn’t seem to be as many as there once was. So sad.

Susan Higgins

Hi Gary, we’re so glad you enjoyed it! Yes, we called them lightning bugs, too. We also ran another story in early spring about what causes them to “appear” and it’s all about the weather — this might answer the question about why you haven’t seen as many. Take a look: Are Fireflies Disappearing?

Eric Albach

There really are flashing fireflies in the west but you have to know where to look. It has often been said that there are none west of Kansas or none west of the Rocky Mountains but I have seen 8 different locations within 30 minutes drive from my home in Utah. They are just being rediscovered here but older people I know who grew up on farms here used to catch them when they were children. One of those was catching them 80 years ago. I only learned about fireflies in Utah about 4 years ago when there was a local newscast about it. I have lived here since the 1960’s and was always told that there are no fireflies. Now I go out many nights during the summer to help discover new locations. The Utah Museum of Natural History website started a map that shows more than 100 reported locations all over the state. Do a Google search for Utah Firefly map. They are even in southern Utah in the desert near Moab and Lake Powell but always near water as expected. There are many reports in all of the other western states too but I haven’t seen them there myself yet. Another good map of fireflies in the U.S. is found by googling Museum of Science Firefly Watch.

Warren Bergmann

My wife and I, here in SE Wisconsin, notice that every time a firefly glows it is rising — never flying level or descending. Can anyone tell us why?

Tom Delaney

Well start breeding fireflies to light up Tenney Mountain for night Skiing


My dad used to tell us to count how many flashes in a period (I have forgotten now) to tell how many days/hours until a rain, or until a thunderstorm. Is there some legend about this? I don’t remember the formula now…………..


Thank you for this article , really enjoyed it. My husband and I found it very interesting. One question though . Why do the fireflies not light up in the Western United States ?


I enjoyed reading about the fireflies and did not know there were different colors of them I can still smell that odor they put off as I played with them as a kid. We would put in a jar and cut holes in the lid.We would have to let them go at bedtime too.


As i was reading your comment i suddenly could remember that stink. LOL. thanks. i had forgotten about that.)

suzy mapes

When I was growing up here in Ne. we always had lots of lighting bugs and had a blast catching them and letting them go … But kids now look at you crazy Just don’t see them very often


Sometimes I sit on the porch and watch the backyard light up with tiny blips of green. As kids we used to catch them in an open jar and watch them blink.


YOU CANT SPRAY STANDING WATER….Most species of fireflies thrive as larvae in rotting wood and forest litter at the margins of ponds and streams. And as they grow, they more or less stay where they were born. Some species are more aquatic than others, and a few are found in more arid areas—but most are found in fields, forests and marshes. Their environment of choice is warm, humid and near standing water of some kind—ponds, streams and rivers, or even shallow depressions that retain water longer than the surrounding ground.


Most species of fireflies thrive as larvae in rotting wood and forest litter at the margins of ponds and streams. And as they grow, they more or less stay where they were born. Some species are more aquatic than others, and a few are found in more arid areas—but most are found in fields, forests and marshes. Their environment of choice is warm, humid and near standing water of some kind—ponds, streams and rivers, or even shallow depressions that retain water longer than the surrounding ground.

Maggie S.

Dear Amber,
Thank you for your insightful article on fireflies. I can’t wait share it with my new 2nd grade class when school begins in August. Do you know that my former 2nd grade class (Room 23) at Cumberland Elementary School in West Lafayette, IN has been lobbying Indiana legislators since February to make the Firefly Indiana’s Official State Insect in 2016? State Representative Sheila Klinker has promised to draft a bill during the next legislative session to hopefully establish the Firefly Indiana’s State Insect in 2016. We are hoping that State Senator Ron Alting will do the same in the Senate. Our class has a Facebook page asking viewers to Support Kayla & Cumberland-Firefly for State Insect 2016, so please ask your readers to check it out! THANKS!!!


I have always thought fireflies were so neat. Even now as a senior I like them. It’s just so relaxing to sit and watch them light up my back yard here in NE Georgia. This year has been very different. I have never seen so many in one place at one time. Each night for the last couple of weeks I have sat on my back deck watching what I call the “light show”. I have even brought my husband and even my son when he has visited, outside to watch the light show. You have to catch it at just the right time because it doesn’t last long and then they are gone for the night. It’s an amazing sight.

Elaine Winegardner

When my boys were small and we lived out in the woods, they would catch these and smear the florescent goo of these bugs on their faces and glow for hours trying to scare their little sister. Cheap form of entertainment for country kids!

Carol Soos

I didn’t realize their life span was so short. As a kid I to would capture them, enjoy their lighting show and sadly let them go when mom said time for bed. I too have noticed they’re not as many so it seems. The light in the area would make a big difference. Luckily we live in an area where it is mostly dark at night. No street lights, just some old fashion lampposts spread far apart as you go down the street. Thanks for your great article. It’s always fun to learn more about things around us that share our planet.

Sylvia Jean

That was great! The last time I saw fireflies is when I went camping at the Age of 13 — I was mesmerized by their beauty!


Thanks for the great article Amber and Farmers Almanac.

krohn traversie

Are there Lightening bugs in Washington State, Yakima County / 98930

Melanie C.

Our community sprays for mosquitoes, unfortunately. One night when I walked thru my back yard, there were the lights of the fireflies all over the ground, I investigated and found that they were all laying on their backs dying. They had just sprayed earlier that evening. We have not been able to convince our city that education about eliminating standing water, is the best way to stop West Nile Fever, not toxic pesticides.

sharon finney

I miss seeing lighting bugs since I now live in Colorado….I am from Indiana….we had so many enjoyable and memorable evenings during the summer, as kids….One year, when I went back home, my kids and I brought some back to Colorado and they actually lived thru the summer…we released them along the Green Belt where we lived, and we would watched them during the warm summer evenings…it was so amazing to see them here in Colorado, for a short time.

Jamie Lynch

I live in the Southern part of Indiana and this past week I seen something I had not seen before. While driving in the country I spotted several tall trees filled with lightning bugs. They made the trees look like Christmas trees. It was almost magical. I am only sorry it would not show up in any pictures.

LA Donna

I loved those summer nights me and my brother would be ready to go out side and chase the lighting bug.. Some kids would make a ring out of them and it would shine for ever. But my brother and i would see how many we could catch in a jar and who ever had the most we win, but we let them go again.
Their are some states that they don’t come to that”s sad because to me that’s what makes summer.


We have tons of lighting bugs here in Laporte, IN. It is so beautiful to watch them over the field at night! It amazes me how many there are.


My favorite!!


I live 2 hours from Gatlinburg, the Synchronous Firefly show is a Huge attraction in the summer. People who live in areas where there are no fireflies flock down here to see them every year. There is a very small one week window where you can see the light show. It’s magical. I’m blessed to. Live in such a beautiful place.

Rita DeWitt

Summers wouldn’t be right without the lightning bugs filling the sky at night. What a miracle! I remember catching them as a child marveling at their light!

Mindy Holverson

Grandpa used to say:
“The lightning bug is brilliant, though he hasn’t any mind….he travels through existence with his headlight on behind” 🙂

Rick Fedoruk

Very good piece on fireflies. Its never really summer to me unless I take a stroll in the forrest behind my house at night, enjoying the glow of the fireflies.


We moved to central Florida in 1989 from western New York and haven’t seen a firefly in 26 years. Except when we visit family in southern Ohio.

Surf Doggy

Wonderfully enlightening article! TY☺


Back in the ’50s my grandmother and I used to lie in a dark, side yard and just talk as we pointed out and counted the fireflies. This brings back some wonderful memories.

Ana Castellon

This is really so cool!!! I also read somewhere many years ago that fire flies are important to the environment somehow and also to mate it must be completely dark their numbers have sharply decreased over the years because of artificial lighting all over the place these environments are no longer natural to these wonderful creatures whom I love!!!

Deborah Tukua, editor Journey to Natural Living

Interesting and beautiful to watch. We enjoy watching the vast number of fireflies in the evenings as they rise from the grassy meadow and twinkle.


when I was a kid in late 40s early 50s there used to be a lot of them
along middle texas coast in spring an summer..now you only see a few..
what happened to them ?

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