Why do fireflies glow?

Fireflies, also known a lightning bugs, have been captivating humans for centuries with their enchanting lights on summer nights.
Insects have a vivid history within folklore and mythology. Butterflies, bees, scarabs and other bugs have become symbolic markers of rebirth, purity, life and death, and the firefly is no exception.
In ancient Amazonian mythology, their light came from the gods and provided hope and guidance while, in Japanese legend, two species of firefly, the Genji-hotaru and the Heike-hotaru, are associated with the ghosts of the Minamoto warriors and the Taira warriors. Still today every year in Japan several viewing festivals start up during the month of June to see the “battle of the fireflies.” There’s also a Japanese legend that lightning bugs are actually the souls of the dead. Variations on the tale say that, not by chance, they’re the spirits of warriors who fell in battle.

Fireflies, in ancient times, were also believed to offer universal remedies, counteracting poison and driving away evil.
In China, long ago, it was believed that fireflies were a product of burning grasses. Ancient Chinese manuscripts hint that a popular summer pastime was to catch fireflies and put them in a transparent box, to use as a lantern, much like children (and adults) often do today.
Fireflies appear in a lot of Native American folklore as well. There’s an Apache legend in which the trickster fox tries to steal fire from the firefly village. To accomplish this, he fools them and manages to set his own tail on fire with a piece of burning bark. As he escapes the village, he gives the bark to hawk, who flies off, scattering embers around the world, which is how fire came to the Apache people. As punishment for his deception, the fireflies told fox that he would never be able to use fire himself.

Today nearly 2,000 species of fireflies live worldwide and inhabit every continent except Antarctica.
And fireflies aren’t actually flies at all, for that matter, they’re not even really bugs, either. In fact, from a biological standpoint, they’re beetles from the family Lampyridae, which in Latin means literally “shining fire”. This “fire” that makes fireflies so fascinating is actually a method of communication, but what’s most fascinating is that this insect can produce light (called bioluminescence) which is relatively rare, and they form a beautiful language with it, as opposed to many animals’ languages made of sounds and scents.
All fireflies are bioluminescent as larvae, which is why the larvae are often called glowworms, but not all of them shine as adults. A lightning bug’s flash can be yellow, green, or even blue, while the fireflies that lose their ability to make light use scent to communicate instead.
The glow is produced in hotocytes, or light cells, in the insect’s abdomen, and the light, the result of the chemical reaction of bioluminescence, occurs when two substances, luciferin and luciferase, react with one another if exposed to oxygen.
A firefly regulates the flow of oxygen into its abdomen, which allows it to turn its taillight on and off.
Interestingly this cold, living light is almost 100% efficient, losing only a fraction of its energy to heat. By comparison, a standard incandescent light bulb is less than 10% efficient, and an LED ranges between 40 and 50% efficient!

Science aside, these beautiful insects come out once dusk begins in the summertime, and can be seen lighting up the night in many areas of the world.
The main purpose of a firefly’s light display is to attract a mate. Only the males fly around while turning their lights on and off, hoping to get the attention of a flightless female waiting in low vegetation.
And 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 glow. The brighter the female’s response, the more interest she has in her suitor.
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” because they mimic the flashes of females of other firefly genera. The unsuspecting courting male flies in (expecting romance) and is promptly eaten.
However, a firefly’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, and their warning can be seen also in the dark.
But fireflies taste horrible to predators like birds and mice. The luciferin that makes them glow tastes noxious to most animals who would snack on them, who have learned over time that a glowing bum equals a nasty dinner.

Fireflies are most abundant in the eastern half of the continent, from Florida to southern Canada, but different species can be found anywhere.
They like meadows and marshes and fields and prefer cool, damp, dim conditions and with very little light pollution, but they 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.
There was a Victorian tradition that if a firefly got into your house, someone was going to die soon.
Of course, the Victorians were pretty big on death superstitions, and practically turned mourning into an art form, so don’t scare too much if you find a firefly in your home some warm summer evening…