12 Things You Didn't Know About Fireflies

From their biology to their behavior, fireflies can be enlightening bugs.

Fireflies in the summer in Thailand
Fireflies are at their most dazzling on a summer evening.

Thanatip S. / Shutterstock

There are many wonders to behold in the animal world, but few offer such enchantment as a summer evening punctuated with the twinkle of fireflies. It's a singular experience, like handfuls of Lilliputian stars tossed from the sky, falling to flit and hover among the grass and brambles. But even behind their charming facade, fireflies are fascinating little insects. Consider the following facts:

1. They Are Beetles, Not Flies

Fireflies are nocturnal members of Lampyridae, a family of insects within the beetle order Coleoptera, or winged beetles. Yes, they are officially beetles. We’re OK with the misnomer, though, since “firebeetles” just doesn’t have the same ring to it. And bonus fact: The family name, Lampyridae, comes from the Greek "lampein," meaning to shine ... just like a lamp.

2. They Are Alchemists, Poetically Speaking at Least

While they don’t actually turn base metals into gold, they do create light as if by magic. When a chemical called luciferin (note the same Latin root as Lucifer) inside their abdomen/tail combines with oxygen, calcium, and adenosine triphosphate, a chemical reaction occurs that creates their spectacular light. (And then Mother Nature said, "Let there be bioluminescence!")

3. Fireflies Exist in the Western U.S., but Most Lack the 'Fire'

Fireflies occur in temperate and tropical habitats all over the world, on every continent but Antarctica. More than 2,000 species are known to science, with about 170 documented in the United States and Canada. These tend to be concentrated in the wetter environments to the east, with much of western North America seemingly devoid of fireflies. The West does have fireflies, however, just not as many that produce light as adults. Many Western fireflies don't light up, or just keep a very low profile, although scientists are still discovering new species.

4. They Are Light Geniuses

firefly lighting up
Firefly light is incredibly efficient. Terry Priest / Flickr / CC BY-SA 2.0

The light produced by the firefly is the most efficient light ever made. Almost 100% of the energy in the chemical reaction is emitted as light; in comparison, an incandescent light bulb only emits 10% of its energy as light, the other 90% is lost as heat.

5. They Are Flashy Flirts

Each species has a specific pattern of light flashing, and males use this pattern to let the ladies of the same species know they would be a fine match for one another. When a female notices a suitable suitor, she replies with her own species-specific flash. Females may also use flash information to decide which male to mate with. And then, fireworks!

6. Some Species Synchronize Their Flashing

As if fairy-like woodlands weren’t made wonderful enough by the glittering glow of fireflies, some species actually synchronize their flashes in a beautiful light show. Hello, firefly disco! Scientists can’t say for sure why fireflies sync up, but it may be the result of competitive males trying to be the first to flash. Or maybe it's because flashing the species pattern in unison will ensure females of the same species notice the gang of randy males. Photinus carolinus are the only species in America that flash simultaneously; one great place to see them is at the Great Smoky Mountains National Park, which has firefly tours. Watch synchronous fireflies in the video above.

7. They Come in a Rainbow of Colors

Well maybe not the whole spectrum, but they do come in yellow, light red, green, and orange.

8. They Taste Disgusting

Not that we were planning on snacking on fireflies anytime soon, but for predators who might like a light meal, beware the lightning bug. Firefly blood contains lucibufagins, which sounds like something out of a Harry Potter book, but is actually a defensive steroid that tastes really gross. Predators associate the bad taste with a firefly’s light and learn not to eat bugs that glow.

9. They Light up the Underworld

Or underground, at least. While it's true that many insect larvae live underground, firefly babies have them beat in the "neat tricks" department, since some species emit a subterranean glow. Among certain species, even the eggs glow.

10. Some Are Aquatic

And then there are the freaky fireflies whose larvae live in the water; they have gills and sup on aquatic snails, before inching their way to terra firma for their next phase in life.

11. They Have Strange Diets

firefly on a flower
Most fireflies live on pollen and nectar. Courtney A Denning/Shutterstock

It's nice to imagine cute baby fireflies nibbling on flowers, but the underground-dwelling larvae are carnivorous. They primarily eat slugs, snails, and worms. Once they grow up, some move on to cannibalism and eat other fireflies, even using their bioluminescence to lure their prey. Most adult fireflies likely subsist on pollen and nectar, though, or may not eat anything during their relatively brief life stage.

12. Their Numbers Are Declining

If you’re seeing fewer fireflies each summer, you’re not alone. Anecdotal evidence suggests firefly populations may be on the decline in many places, most likely due to a combination of light pollution, pesticide use, and habitat destruction.

Save the Fireflies

  • Turn off outdoor lights at night to reduce light pollution.
  • Avoid pesticides, especially broad-spectrum insecticides.
  • Mow your lawn less often, or leave sections of taller grass, so fireflies have safe places to rest on the ground. Woody debris and water features can also help.
  • Plant native trees like pine, whose canopy creates dimmer conditions that might allow fireflies to begin flashing earlier on summer evenings.