10 Fascinating Facts About Fireflies

Light is used to draw prey and sex partners and to warn off predators

Fireflies

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Fireflies, or lightning bugs, are from the family Coleoptera: Lampyridae and they might be our most beloved insect, inspiring poets and scientists alike. Fireflies are neither flies nor bugs; they are beetles, and there are 2,000 species on our planet.

Here are other interesting facts about fireflies:

Flight

Like all other beetles, lightning bugs have hardened forewings called elytra, which meet in a straight line down the back when at rest. In-flight, fireflies hold the elytra out for balance, relying on their membranous hindwings for movement. These traits place fireflies squarely in the order Coleoptera.

Efficient Light Producers

An incandescent light bulb gives off 90% of its energy as heat and only 10% as light, which you'd know if you've touched one that's been on for a while. If fireflies produced that much heat when they lit up, they would incinerate themselves. Fireflies produce light through an efficient chemical reaction called chemiluminescence that allows them to glow without wasting heat energy. For fireflies, 100% of the energy goes into making light; accomplishing that flashing increases the firefly metabolic rates an astonishingly low 37% above resting values.

Fireflies are bioluminescent, meaning they are living creatures that produce light, a trait shared with a handful of other terrestrial insects, including click beetles and railroad worms. The light is used to attract prey and members of the opposite sex and to warn off predators. Lightning bugs taste bad to birds and other potential predators, so the warning signal is memorable for those that have sampled before.

'Talk' Using Light Signals

Fireflies don't put on those spectacular summer displays just to entertain us. You're eavesdropping on the firefly singles bar. Male fireflies cruising for mates flash a species-specific pattern to announce their availability to receptive females. An interested female will reply, helping the male locate her where she's perched, often on low vegetation.

Bioluminescent for Life

We don't often see fireflies before they reach adulthood, so you might not know that fireflies glow in all life stages. Bioluminescence begins with the egg and is present throughout the entire life cycle. All firefly eggs, larvae, and pupae known to science can produce light. Some firefly eggs emit a faint glow when disturbed.

The flashing part of fireflies is called a lantern, and the firefly controls the flashing with neural stimulation and nitric oxide. The males often synchronize their flashes with one another during courtship, a capacity called entraining (responding to an external rhythm) once thought only possible in humans but now recognized in several animals. Colors of firefly lights range widely among different species, from yellow-green to orange to turquoise to a bright poppy red.

Lives Spent Mostly As Larva

The firefly begins life as a bioluminescent, spherical egg. At the end of the summer, adult females lay about 100 eggs in soil or near the soil surface. The worm-like larva hatches out in three to four weeks and throughout the fall hunts prey using a hypodermic-like injection strategy similar to that of bees.

Larvae spend the winter below ground in several types of earthen chambers. Some species spend more than two winters before pupating in late spring, emerging as adults after 10 days to several weeks. Adult fireflies live only another two months, spending the summer mating and performing for us before laying eggs and dying.

Not All Adults Flash

Fireflies are known for their blinking light signals, but not all fireflies flash. Some adult fireflies, mostly those in western North America, don't use light signals to communicate. Many people believe that fireflies don't exist west of the Rockies since flashing populations are rarely seen there, but they do.

Larvae Feed on Snails

Firefly larvae are carnivorous predators, and their favorite food is escargot. Most firefly species inhabit moist, terrestrial environments, where they feed on snails or worms in the soil. A few Asian species use gills to breathe underwater, where they eat aquatic snails and other mollusks. Some species are arboreal, and their larvae hunt tree snails.

Some Are Cannibals

What adult fireflies eat is largely unknown. Most don't seem to feed at all, while others are believed to eat mites or pollen. We do know that Photuris fireflies eat other fireflies. Photuris females enjoy munching on males of other genera.

These Photuris femmes fatales use a trick called aggressive mimicry to find meals. When a male firefly of another genus flashes its light signal, the female Photuris firefly replies with the male's flash pattern, suggesting she is a receptive mate of his species. She continues luring him in until he's within her reach. Then her meal begins.

Adult female Photuris fireflies are also kleptoparasitic and can be seen feeding on silk-wrapped Photinus species fireflies (occasionally even one of their own kind) hanging in a spider's web. Epic battles can occur between the spider and the firefly. Sometimes the firefly can hold off the spider long enough to consume the silk-wrapped prey, sometimes the spider cuts the web and her losses, and sometimes the spider catches the firefly and the prey and has them both wrapped in silk.

Enzyme Used in Medicine

Scientists have developed remarkable uses for firefly luciferase, the enzyme that produces bioluminescence in fireflies. It has been used as a marker to detect blood clots, to tag tuberculosis virus cells, and to monitor hydrogen peroxide levels in living organisms. Hydrogen peroxide is believed to play a role in the progression of some diseases, including cancer and diabetes. Scientists now can use a synthetic form of luciferase for most research, so the commercial harvest of fireflies has decreased.

Firefly populations are shrinking, and the search for luciferase is just one of the reasons. Development and climate change have reduced firefly habitats, and light pollution depresses the ability for fireflies to find mates and reproduce.

Flash Signals Synchronized

Imagine thousands of fireflies lighting up at the same time, over and over, from dusk to dark. Simultaneous bioluminescence, as it is called by scientists, occurs in just two places in the world: Southeast Asia and Great Smoky Mountains National Park. North America's lone synchronous species, Photinus carolinus, puts on its light show annually in late spring.

The most spectacular show is said to be the mass synchronous display of several Pteroptyx species in Southeast Asia. Masses of males congregate in groups, called leks, and in unison emit rhythmic courtship flashes. One hot spot for ecotourism is the Selangor River in Malaysia. Lek courting happens occasionally in American fireflies, but not for long periods.

In the American Southeast, male members of the blue ghost firefly (Phausis reticulate) glow steadily as they fly slowly over the forest floor searching for females, from about 40 minutes after sunset until midnight. Both sexes emit a long-lasting, nearly continuous glow in the forested regions of Appalachia. Annual tours to see the blue ghosts can be taken at state forests in South and North Carolina between April and July.

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