Fireflies: Why Do Fireflies Glow?

Lightning Bugs Facts and How to Attract Them

By George and Becky Lohmiller
August 17, 2019
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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 …

Why Do Fireflies Glow?

  • Photocytes, or light cells, in the insect’s abdomen are where the glow is produced.
  • The light, the result of the chemical reaction 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 to turn its taillight on or 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!
  • The main idea 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 lightning bug’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 these 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

Leave a Comment

Your Firefly Article

The last time I was fortunate enough to personally see fireflies was on the 4th of July, 8 years ago. I was in a very marshy area a half mile away from the town firework show...fewer people, less traffic..old dirt road. Then I seen them. I swear, the joy that swelled within me made me downright giddy. My daughter was 4 and she was just as amazed. It was quite the experience, even better than fireworks....sadly, for us, the mosquitoes found every inch on us that we missed with the repellant and we were only able to tolerate 2hrs of happiness. I can't really make my proerty firefly friendly by adding watersources, heck, I had to put plants in my stone birdbaths because the mosquitoes breed so profusely. It's a shame. I loved the article though...maybe someday. Closing on a positive note, I have become a milkweed junkie and strive to release as many Monarch Butterflies as possible yearly. Aphids are no match fo me. I dab q-tips in Alcohol and dab the aphids. Dead in minutes. Keep spreading the joy of fireflies!!

Fireflies

We saw fireflies in February here in Mississippi. While they may taste bad to birds and mice, apparently not to bats as we have seen them eat the fireflies in flight. Stinking ole bats!

Fireflys

I like watching them as in the early evening, they start around ground level. But as it gets darker, they'll "Congregate" up in the trees. Then they look like the LED lights for Christmas trees flashing up in the trees. I never did like the lights to stay on, but I liked when they flashed. And at times, there were so many, it looked like the entire trees were just flashing constantly. They are beautiful and fun to watch, and NO, I don't catch them and put them in jars ANYMORE. haha

fireflies

In NE San Antonio, TX, the last two springs (2016, 2017) have brought us clouds of fireflies! It has been enchanting partly just to sit outside to watch them and partly to sit and remember chasing them as a delighted (and determined!) child. The winters those years were mild and a little wetter than others which may have been helpful. (Note, most of the yards in my neighborhood use little, if any, toxins on the yards - also helpful.)

Fireflies

Still see a few each summer in our back yard that backs up to a rather dense area of woods. Not nearly as many as years ago. We love watching them and wish there were more.

Fireflies

I live in Texas. In some areas the light is in their tail, and in others their head. I love to watch for them on Summer nights. Very peaceful.

thanks

very nice article, thanks a lot

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