10 Facts About Fireflies You May Not Have Known

June 27, 2022  |  Permalink

fireflies at EESP

Fireflies lighting up a June night at Edgar Evins State Park

In honor of upcoming World Firefly Day (which falls on July 3rd/4th this year), I wanted to spend some paragraphs highlighting these special arthropods. While not everyone is a fan of insects, there is one that seems to win the hearts of young and old alike. Most insects get attention by either directly benefiting us (like pollinators) or by having a negative impact (such as disease-carrying ticks); but fireflies are neither. They enrich our lives simply by existing and flashing their ethereal lights on warm summer nights. For this reason, we call these bioluminescent organisms charismatic insects.

snappy sinc firefly

A Snappy Sync firefly (Photuris frontalis) flashes a path through the woods at Edgar Evins State Park

However, there is much more to these animals than meets the eye. They are fascinating on so many levels that I wanted to break down some of the top facts about fireflies that you may not have been aware of...


1. They are neither a fly nor a bug. We know them as fireflies or lightning bugs, but did you know they are actually beetles? They are in the family Lampyridae, close relatives of soldier beetles. If you catch a firefly and let it crawl up to your finger, watch it lift its elytra, or hard wing coverings, before they unfurl their wings folded up underneath and fly away. These elytra are one thing that all adult beetles have in common.

snappy sync closeup

A closeup of a Photuris' elytra

2.  Not all fireflies light up as adults. To be considered a firefly you have to light up in at least larval stage. There are actually numerous firefly species that lack lanterns, the bioluminescent organs, and find each other by using pheromones with their larger antennae. Many of these species are active during the daylight hours, and some can be seen visiting flowers for nectar or flying through the forest.

winter firefly

The Winter Firefly (Ellychnia) is active during the day and lacks glowing organs (lanterns) on its abdomen

winter firefly underside

3. There are many different species. As a matter of fact, in the state of Tennessee there are at least 30 different firefly species. Some emerge in a single generation at a specific time of year. The earliest emerging firefly is usually the Spring Treetop Flasher (Pyractomena borealis). Some emerge gradually and are active during much of the warm season. Identification of fireflies isn’t always so straightforward, but their size, color, seasonality and especially their flash pattern, are helpful for narrowing down the species. My absolute favorite has to be the Blue Ghost (Phausis reticulata) which typically flies in late spring and early summer. While it was once thought to only reside in the highest elevations of the state, populations are now being discovered statewide. It is unique for holding a steady, bluish glow, rather than flashing. They can stay lit up to a minute as they trace a silent path only a few feet above the forest floor. Peak nights of Blue Ghosts are absolutely breathtaking.

blue ghosts

4. Our Tennessee State Insect. In 1975 the Firefly, along with the Ladybug, was designated our state insect. More specifically, it is the Common Eastern Firefly (Phontinus pyralis), which is active throughout most of the late spring and early summer months. It is highly adaptable and widespread, which makes it our most ubiquitous and familiar firefly. In fact, this is the one most of us grew up catching in our backyards, since they fly just a few feet above the ground, flashing in a “lazy J” pattern.

5. Some are pollinators. Most fireflies eat very little, if anything, during the adult phase of their lives. With the exception of a few predatory species (we’ll get to that later), they mostly sip on dew, plant sap or nectar. Some daytime species spend enough time visiting flowers for nectar and pollen that they can be effective pollinators.

flower elf

This little daytime firefly is known as the Flower Elf (Pyropyga minuta)

6. They undergo complete metamorphosis. Like other beetle species, their life cycle can be divided into 4 distinct stages: egg, larva, pupa and adult. While not all species light up as adults, they all glow during the larval stage, and some even glow as eggs! Like many insects, fireflies spend most of their lives as larvae, hiding in the leaf litter or underground during the daylight hours and prowling for prey at night. You can often see their soft glow on the ground in moist areas after dark. (For this reason they are often referred to as glow worms.) They typically overwinter in the larval stage and complete their metamorphosis the following year. An individual adult firefly lives for only about 3-4 weeks.

pyractomena larva

7. They are toxic. The chemical that facilitates the reaction causing a firefly’s signature bioluminescence is called luciferin. It not only provides the spark to help lovestruck fireflies find each other in the dark, but it is also a distasteful chemical defense. If you catch a firefly you may notice droplets of this thick, white substance seeping out from their bodies. Not too many things eat fireflies as a result. Believe it or not, it could take as few as 20 fireflies to provide a fatal dose of luciferin to an adult human!

8. Firefly larvae are voracious predators. If you were to uncover a firefly larva, you may not have any idea what the little bizarre armored alien was! Baby fireflies look absolutely nothing like the adults, and their appearance will be different depending on what genus they are in. Those in the genus Pyractomena are the most interesting-looking, in my opinion. They often feed on soft-bodied snails, worms and slugs, prowling in moist areas at night. 

pyractomena and snail

A Pyractomena larva chowing down on a juicy snail

photuris larva

A Photuris larva

9. Some are cannibals. While we consider fireflies to be mild-mannered, harmless night lights, there lurks a femme fatale in their midst. Female fireflies in the genus Photuris cannot manufacture their own luciferin, the toxic, bioluminescent chemical found in other species. To obtain it she uses the tactic of mimicry, imitating the flash patterns of a female Photinus firefly to lure in the unsuspecting, lovesick males. Once within her grasp she strikes, consuming him alive until she has obtained the desired amount of Luciferin that she will pass on to her children.

Photuris firefly

A Photuris firefly

10. They are disappearing. Older generations may have noticed that there aren’t as many fireflies flashing as there were when they were children – and it isn’t their imagination. Fireflies, like all insects, are declining worldwide. Habitat loss, pesticides and light pollution are all major contributing factors to their disappearance. Collecting for laboratory research also has a negative impact on firefly populations. Luciferin can now be manufactured synthetically, but some laboratories still offer monetary rewards for capturing hundreds of fireflies for research purposes. Creating habitat for fireflies in your own backyard is as simple as eliminating or reducing pesticide use, leaving leaf litter and wild edges as habitat, and reducing light pollution so they can find each other during the breeding season.

If you would like to learn more about fireflies and other glowing invertebrates, be sure to check out the book “Fireflies, Glow-worms and Lightning Bugs"  by Lynn Frierson Faust.

firefly book

This 4th of July weekend, try to take a break from the loud gunpowder fireworks and enjoy some of natural, silent lights sparkling in our fields and forests.

I would like to leave you with my favorite haiku by Shei Sanchez…..


Moonless night

Flying stars everywhere –

Beetles in love.

firefly long exposure

About the author

holly headshot

Holly Taylor got her start with Tennessee State Parks as a Seasonal Interpretive Ranger in 2006, working six years at Edgar Evins State Park before working as a wildlife presenter for the Natural History Education Company of the Mid-South. She took time off to stay at home with her son before returning to TN State Parks as the assistant to State Naturalist Randy Hedgepath in 2018. She graduated from TTU in 2009 with a B.S. in Conservation Biology and also serves as the chapter coordinator for the Cumberland Mountain Chapter of the Tennessee Naturalist Program. She has a life-long passion for the natural world and loves nothing more than sharing that passion with others.