Fireflies: Why Do Fireflies Glow?

Lightning Bugs Facts and How to Attract Them

By George and Becky Lohmiller
June 4, 2020
fireflies-lightning-bugs

Fireflies light up a forest night. Why do fireflies glow?

University of Florida

Fireflies—also known a lightning bugs—have been captivating humans for centuries with their beautiful lights on summer nights. What makes fireflies glow the way they do?

The nearly 2,000 species of fireflies worldwide inhabit every continent except Antarctica. The firefly isn’t actually a fly at all, but rather a beetle from the family Lampyridae, which in Latin means “shining fire.” This “fire” that makes fireflies so fascinating is really a method of communication for the insects.

What’s most fascinating is that this living organism can produce light (called bioluminescence) which is relatively rare. And they form a beautiful language with light (as opposed to many animals’ languages of sound and scent). What signals are they sending? Let’s explore …

How Do Fireflies Glow?

Photocytes, or light cells, in the insect’s abdomen are where the glow is produced.

This light, the result of the chemical reaction of bioluminescence, occurs when two substances, luciferin and luciferase, react with one another when exposed to oxygen. The firefly regulates the flow of oxygen into its abdomen, which allows it to turn its taillight on and off.

This cold, living light is almost 100 percent efficient, losing only a fraction of its energy to heat. By comparison, a standard incandescent light bulb is less than 10 percent efficient, and an LED ranges between 40 and 50 percent efficient!

Why Do Fireflies Glow?

The main purpose of a firefly’s light show is to attract a mate. The males fly around while turning their lights on and off, hoping to get the attention of a flightless female waiting in low vegetation. They try to flash very quickly, because this is what attracts females.

If a female is impressed by a male’s flickering, she will flash back a response to the twilight glow. The brighter the female’s response, the more interest she has in the male. 

Each species of firefly has its own unique flash that is characteristic of its sex and species. Carnivorous females of the genus Photuris are known to entomologists as “femmes fatales.” These fireflies mimic the flashes of females of other firefly genera; the unsuspecting courting male flies in (expecting romance) and is promptly eaten.

A firefly’s light can also serve as a warning to predators. In the same way that bees scream “Danger!” with their black and yellow stripes, fireflies show their toughness with their light. Fireflies even have an advantage over bees, because their warning can be seen in the dark!

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Photo Credit: Wesleyan University. Fireflies are often found in meadows or next to creeks, as they like damp areas.

How to Find Fireflies

Fireflies are most abundant in the eastern half of the continent, from Florida to southern Canada, but different species can be found anywhere in North America.

  • They like meadows and marshes and fields and prefer cool, damp, dim conditions.
  • They rely on that habitat remaining undisturbed for the year or more it takes them to complete their life cycles which is why their habitat can easily disrupted by logging and development. Unfortunately, many wingless species can’t disperse any further than they can walk, so they can’t easily re-establish. Habitat destruction is one of the greatest threats to fireflies.
  • Try to find an area with very little light pollution: a meadow, the edge of a forest, or even your backyard if you don’t live in an urban area. Also, keep the outdoor lighting at your home dim.
  • Go out to look for fireflies soon after sunset. If you stand still and watch carefully, you just might see a few!
  • Fireflies don’t come out until the warmth of spring, so wait until the spring and summer months of May, June, and July to search for them.

One downside to firefly watching is that mosquitoes also like the same conditions. Unfortunately, some common methods of deterring mosquitoes (like using a pesticide) also kill fireflies and are another reason for their decline.

How to Attract Fireflies

The best way to attract these blinking bugs is to turn your yard or garden into the ideal firefly environment:

  • Fireflies appreciate shrubs and low trees for daytime shelter, so consider planting some to keep them around.
  • Fireflies like to hang out in grassy meadows, so if you want them to visit your property, let some parts of your lawn grow out or plant tall ornamental grasses. They enjoy perching on the tips of long blades of grass while searching for a mate. 
  • Place bird baths in grassy areas or near shrubs; fireflies will appreciate the water source. 
  • Don’t use mosquito-repelling chemicals in your garden, as these will also repel fireflies.

More Fun Firefly Facts

  • Fireflies taste horrible to predators like birds and mice. They release a bitter defensive chemical when eaten, which helps to keep predators away.
  • All fireflies are bioluminescent as larvae (which is why the larvae are often called glowworms), but not all of them shine as adults. The fireflies that lose their ability to make light use scent to find mates instead.
  • Even though a firefly’s light is triggered by oxygen, fireflies do not have lungs. Instead, they inhale oxygen through tubes called “tracheoles.”
  • A lightning bug’s flash can be yellow, green, or even blue!
  • Fireflies are only about ½ inch long, and they have very big eyes so that they can see the flashes of other fireflies.
  • Fireflies (as well as their larvae, glowworms) help to control garden pests like snails, slugs, cutworms, and aphids, so be sure to keep them around if you have them in your garden.

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Photo Credit: Clemson University. It is important to protect beneficial firefly populations, so be sure to release them from jars.

Though many people love to catch fireflies in jars and keep them around, fireflies can be much more beneficial in your yard than in your house. Even if you keep them in a jar for a few hours, be sure to release them again. And for the effect of putting lightning bugs in a jar without bothering any of them, try our Mason Jar Lid with Star Lights.

Let your love light shine with these dazzling garden friends, and let us know in the comment section if you’ve found lightning bugs in your garden!

Source: 

This page was first published in 2010 and has been updated.

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Reader Comments

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Lightnin’ bugs

We have a small creek that runs through the back of our property here in the Deep South of Georgia. The lightning bugs are usually plentiful back there during the summer months. It’s a wonderful sight to see. Unfortunately the mosquitoes also love the wet ground. They are horrendous!

One interesting thing I've

One interesting thing I've found about fireflies is they always crawl up when you catch them. So you can put them in a jar and turn it upsidedown and they will crawl up to the bottom of it. You can put them in an open style cricket bucket and they won't get out until you lift the center portion. Neat creatures.

Catching Fireflies

When we were kids, we spent summers with our paternal grandparents on their farm in southeastern VA. One year all the cousins were there together and we decided to see who could catch the most fireflies. We each caught a passel and hid the jars until bedtime at which point we released them... IN the house! My grandmother slept on the sofa at that time to be near my great-granny's room which was downstairs. Granny was quite ill and needed frequent attention day and night which she wanted only from Grandma. In the middle of the night, Granny woke and called out and Grandma woke too, to see hundreds of spots before her eyes. She thought she was having a stroke or had some severe eye problem, so she yelled and woke up my mom and aunts who came running. It took my mother about two seconds to realize what we had done, so they woke us all up, and at 1 AM we were collecting fireflies from the walls, drapes, etc. This meant we had to turn the lights on because they stop blinking when it gets really late. Needless to say we didn't get them all that night, but most got caught in a couple of days and returned to the out-of-doors. And we NEVER held a firefly catching contest again.

Fire Flies

We named our land Fire Fly Woods the the nightly show we watch from mid June Thur early July. I have never seen as many as we have in our meadow and woods. It is a nightly show that brings family and friends to watch. So happy to see your article.

Fireflies

We’ve an impressive array of fireflies near the Mississippi and Rock Rivers. I’m concerned, though, because after leaving the porch light on last night (it is on frequently at night), I have numerous small slugs all of a sudden. Ewww. Hope the fireflies get them!!!

Fireflies

My daughter-in-law is from British Columbia and had never seen a firefly until she came to New Brunswick for a summertime visit. She was awestruck when she saw the field lit up with all the fireflies. She couldn't believe that there was so much light just flying around like that. I want to get a video of them for my grandchildren to see because they live in BC and have never seen them either. I'm sure they will be as amazed as their mother was.

FIREFLIES

The first and last time my family ever saw fireflies was 14 years ago while on vacation, of all places in Central Park NYC. It made our visit all the more magical. Just moved to Cumberland, RI less than a year ago and haven’t lived through all the seasons yet. Last night we saw fireflies again in our very own backyard!!!

Fireflies

We’ve been seeing fireflies the last few nights here in Minnesota. It brings back pleasant childhood memories. We moved two miles last fall from “town” to “the country” amazing how much different it is. Less mosquitos here too since so many birds. The fireflies and birds like the hay field our backyard looks onto. We have a couple ponds, some bird baths and lots of shrubs and trees (many which need trimming for esthetic reasons but apparently are supporting nature.)

Fireflies

Enjoyed and found your article on fireflies interesting. As a child we caught them and put them in a jar and used them for a flashlight over night then let them go. As an adult I moved to NorthEastTexas and they come out in May. It's still a delight to watch them. I don't have to do anything to attract them. I live in the country and they are everywhere!

fireflies

We live in a suburban neighborhood in Michigan across the street from a large nature preserve. Our grandson's have loved catching fireflies in our yard. Such a beautiful sight!

Fireflies

Yes we have a lot of fireflies in our garden. I love sitting outside on a warm summers night and seeing their flickering lights. It is such a tranquil feeling however I’ve never seen one with a blue light or a green light only the yellow. I live in eastern PA they are truly one of Gods wonderful creations.

Fireflies

We get them every year, & look forward to seeing them, we get quite a few, they’ll even come & land on your extended hand-pretty cool

Lightening

Yes, last year was my first summer in my little home. There were many lightening bugs. What a wondrous show. I live next to an open field and there are many birds who habitat here.
Thank you for your very informative article.

Learning about lightening bugs

I catch and release them but I try not to put them in a jar. I just keep them in my hand and then help them fly up afterwards. I love lightening bugs and I don't want them to die out. My mom is teaching me about fireflies today and this page was very helpful because I didn't know some of this. Thank you.

Emony (age 7)

Lightning Bugs

I grew up in Illinois, and enjoyed these little guys. It was a sad day when we moved out here to Oregon, because we don't have them out here.

Lightening Bugs

I grew up in a suburb of NY and we had them! Moving to Florida was a mistake!! Don't see them or rainbows here! Living here 14 years has taken out all the fun of 'summer'!

Fireflies

About two nights ago-I saw some oh-so-beautiful fireflies! There must have been dozens of them-all flickering on and off! It was SO beautiful! I haven't seen anything like this since I was a kid! I really hope that it happens to me again-it was absolutely beautiful!

Lightning Bugs

We used to see some in the summer in FL and SC in the 60s and 70s. I now live in N FL, and have not seen one here for the last 15 years. Before that, I would see maybe 3 in a summer. In the late 70s in Orlando, I also did not see any. The last I saw more than a few a season was in the early 70s.

Lightin Bugz

I grew up catchin' Lightin' Bugs an old pickle jar with holes in the lid and have a show all night. I have 3 kiddos of my own and I would clip glow sticks on the back of their shirts so I see where they were out in the field at night. They loved it they said we lightin' bugz too!! They had the lil fancy screened in box for their bugs they would fight on who kept them in their room. Next day turned them loose.

Fireflies vs chiggers

So basically you have to create a chigger-infested environment to have fireflies? :'(

It's already damp, humid, and warm in the summers here in Arkansas. Tall grass is just asking for a chigger invasion.

Fireflies

We live in the N Georgia Mountains and enjoy the fireflies in the summer evenings. They come in waves as some are very bright and some dim but we have the moisture and environment they require. Awesome to view.

FireFlies and Stars

Why is it that there fewer starts and fire flies around now? I mean when i was little if you looked up into the night skies there was thousands of stars in the sky and there was thousands of fireflies everywhere. Now if you look up into the night skies there are so few stars shining and thousands of lighting bugs around.

FIREFLIES AND STARS

Maybe light pollution? Go down dark country roads and the stars are still amazing!

Lightening Bugs

I live in south central Pennsylvania. The lightening bugs returned to my backyard just a few evenings ago. It always makes me a bit sad when they disappear at the end of the Summer, so I always look forward to their return. Love to sit out on my patio in the evening and watch them flashing. We always get quite a few in our backyard.

fireflies

Live in Central Ontario. There used to be many. Haven't seen any for many years.

Fireflies

I've lived in a small town in Tennessee all my life. I couldn't imagine going just 1 summer and not being able to see their beautiful light show. When I was young, like many of the other readers, use to get the mason jar out and have Mom to punch holes in the lid. I'd come back and proudly show her my glowing jar. I'd fall asleep watching them turn their lights on and off for me! Mysteriously they always escaped before the next morning...Thanks Mom!!!

LOVE 'EM

I'm from Tucson, AZ, and I thought fireflies were just a myth until I visited Louisville, KY in August, 1975. I was sitting outside and saw all these little lights flashing around me. I called my boyfriend out, and asked him if he could see the lights. He laughed and caught them in his hands. I couldn't believe them, they were just beautiful.

LOVE 'EM

Thank you for your post, it helps remind those of us who see them all the time to appreciate them more. I don't know why it never occurred to me that there are people who've never seen them.

LOVE 'EM

I'm from Tucson, AZ, and I thought fireflies were just a myth until I visited Louisville, KY in August, 1975. I was sitting outside and saw all these little lights flashing around me. I called my boyfriend out, and asked him if he could see the lights. He laughed and caught them in his hands. I couldn't believe them, they were just beautiful.

Cancer Research

I collected fire flies one summer in Illinois, for a penny a piece and sent them to Missouri for cancer research. I raised $90.00 for my ladies church group.

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