11 Things You Didn't Know About Fireflies

A "galaxy" of fireflies glowing in the woods.
Nori Yuasa / Getty Images

Fireflies, also known as lightning bugs, are the enchanting insects whose bioluminescent abdomens glow at night. A nostalgic symbol of summer in rural North America, these bugs are actually found all over the world — South America, Europe, Africa, and Asia — wherever there's a river, swamp, pond, marsh, or any other sort of standing water. And while they are widely admired for their unique, lantern-like ability, most people aren't aware of the complex processes that allow them to twinkle. Learn how they glow, why the species is declining, and more.

1. Fireflies Are Not Actually Flies

A single firefly up close, wings outstretched, flashing its light.
Ali Majdfar / Getty Images

Contrary to what their name suggests, lightning bugs don't belong to the same family as flies. Rather, they're nocturnal members of the family Lampyridae, within the order Coleoptera, which also contains ladybugs, emerald ash borers, and boll weevils. Simply put, fireflies are soft-bodied, winged beetles. The family name, Lampyridae — which also happens to be the insect's scientific name — even comes from the Greek word "lampein," meaning "to shine."

2. Their Bioluminescence Is Caused by a Chemical Reaction

Luciferin is an enzyme inside the firefly's abdomen and tail area that, when combined with oxygen, calcium, and adenosine triphosphate, creates light. All this happens in the insect's "glow organ," located in the last two or three abdominal segments, and can be controlled by the firefly. It can start or stop the glowing at any time by "breathing" oxygen, which is done through its muscles as it doesn't have lungs. The light can range from yellow to green, light red, and orange.

3. They're Incredibly Efficient

The light produced by fireflies is the most efficient light on earth. According to the National Wildlife Federation, almost 100 percent of the energy from this chemical reaction is emitted as light, whereas an incandescent lightbulb emits only 10 percent of its energy as light while the other 90 percent is lost as heat. Because they couldn't survive if their bodies got as hot as a lightbulb, they produce only about 1/80,000th of the heat emitted by a household candle.

4. Fireflies in the Western U.S. Don't Light Up

Fireflies live in temperate and tropical habitats all over the world, on every continent but Antarctica. More than 2,000 species have been discovered globally and about 170 have been documented in the U.S. and Canada alone, The Xerxes Society says. In the U.S., they are mostly concentrated in the wet environments of the East Coast; however, the West Coast has fireflies, too — except not all light up. According to the California Center for Natural History, Western fireflies glow only during the larval stage.

5. They Use Their Light Patterns To Attract Mates

Each firefly species has its own pattern of light flashing, and males use this pattern to attract females of the same species. The male firefly will know whether a potential mate is interested by how long it takes her to flash back a reply. However, some "femme fatales" will actually trick males with false flash patterns, attacking and eating them when they come closer to mate. The light patterns, according to a study published in a 2008 issue of the Annual Review of Entomology, also help warn predators of the fireflies' bad flavor.

6. Some Species Synchronize Their Flashing

Every summer, Great Smoky Mountains National Park welcomes throngs of tourists seeking a specific species of lightning bug that flashes in unison. They're called synchronous fireflies — aka Photinus carolinus — and they synchronize their flashing with those around them, lighting up the forest with their choreographed blinking. The phenomenon only lasts during the two-week mating period. The National Park Service says scientists haven't pegged down why these fireflies synchronize their light patterns, but it's thought to have something to do with the temperature and soil moisture of the Great Smoky Mountains.

7. Fireflies Have Short Lifespans

From egg to adulthood, fireflies can live up to a year, but they're only capable of flying and laying eggs for about two months of that period. During the larval stage, they hide out in underground burrows (through winter and early spring), emerging as adults to hastily lay eggs (about 500 per female, on average) and then die after five to 30 days.

8. They Taste Bad to Predators

Firefly blood contains lucibufagins, a defensive steroid that tastes bitter to predators like bats, birds, spiders, anoles, and frogs. Predators associate that bad taste with the firefly’s light and, in turn, learn to avoid them. One 2018 study that introduced bats to bioluminescent fireflies for the first time noted that after initially tasting the insects, the bats would shake their heads, salivate, spit, and refrain from eating them again.

9. Some Are Aquatic

While many larvae live in trees and in underground burrows, some species lay their eggs in water. These aquatic larvae crawl and emit green light at the bottom of the water, typically living on aquatic snails before inching their way to terra firma for their next phase in life. They even develop gills. Aquatica lateralis, as they're called, are found in Russia, Japan, and Korea.

10. They Eat Slugs, Snails, and Sometimes Nothing at All

Firefly larvae usually live on slugs, snails, and worms, injecting their prey with a chemical that immobilizes and liquifies them, the National Wildlife Federation says. But when they get older, they switch to pollen and nectar, sometimes resorting to cannibalism or even eating nothing at all, having consumed enough nutrients as larvae to last them throughout their brief adult lives.

11. Their Numbers Are Declining

Fireflies have not been assessed by the International Union for Conservation of Nature and Natural Resources, but research suggests the flickering insect is on the decline. Pesticide use and habitat destruction are to blame for today's dwindling lightning bug population, but above all, light pollution may be the biggest culprit. Outdoor lights can confuse them during mating season, leading to less reproduction.

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 tall 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 their light shows earlier in the evening.