What makes a firefly glow

  • There are over 2,000 individual firefly species, all within the taxonomic family of Lampyridae.
  • But the answer to the lightning bug’s light all happens in the same organ in its abdomen: the lantern.
  • While the firefly may have evolved its lantern as a form of protection, today the lightning bugs use their light as a species-specific mating ritual.
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Following is a transcript of the video.

Narrator: There are over 2,000 individual firefly species, all within the taxonomic family of Lampyridae, which is pretty easy to remember. And these lightning bugs with their flickering light shows make summer nights feel all the more magical and romantic. But how did fireflies manage to catch lightning in a bottle? The answer is found in the bug’s butt, or more specifically in its abdomen, in an organ called the lantern. This organ is a set of specialized light cells, all encased in a translucent exoskeleton. And those light cells are where the magic happens: the phenomenon of bioluminescence, when a chemical reaction in a living thing emits light. Fireflies aren’t the only creatures that have this power. Glowworms and certain deep-sea fish species are some of the creatures capable of producing and emitting light. But the firefly is probably the Earth’s most famous bioluminescent species. So what’s happening inside the firefly’s light cells? What’s the secret to its glow?

In the 19th century, French pharmacologist Raphaël Dubois, working with bioluminescent clams, discovered that there are two essential components to these creatures’ light show. He named them luciferin and luciferase, based on the Latin term lucifer, for “light-bringer.” Luciferin is the compound that generates light, and luciferase is the enzyme that acts on it. Today, we know that the firefly’s bioluminescent reaction plays out like this. A firefly diverts oxygen to its light cells through its tracheoles. And those oxygen molecules react to luciferin, catalyzed with the help of luciferase and energy in the form of ATP. The luciferin then becomes agitated and excited, elevating its energy level. And when the excited luciferin drops back to its normal state, it releases that energy in the form of light, creating the “fire” in fireflies. It’s a remarkable phenomenon that’s also remarkably efficient. In a light bulb, 90% of the energy consumed is given off as heat, with only the remaining energy, a mere 10%, given off as visible light. In a firefly, on the other hand, nearly 100% of the energy is given off as light. That luminescence, or “cold light,” as it’s also called, is produced in the light cells and then focused by a layer of reflector cells, which direct that beam outward through that translucent exoskeleton.

But why do fireflies do what they do? As it turns out, bioluminescence has a number of evolutionary benefits, helping certain marine species lure prey to their mouths or serving as a defense against predators.

Sara Lewis: Fireflies are beetles, and so the juvenile fireflies live underground. So, we think that firefly light first evolved as a warning. It’s like a neon sign that shouts out, “Don’t eat me, I’m toxic.”

Narrator: But in adult fireflies, the purpose is a bit more romantic. Those yellow flashes lighting up our warm summer nights are actually part of the fireflies’ complex mating rituals, with male fireflies attracting female fireflies of the same species by flashing a distinctive, recognizable pattern. So those lights twinkling around you, switching on and off seemingly at random – they’re just the opposite: a highly intricate, specialized form of species-specific seduction.

Lewis: In North America, males might flash, like, just one flash. Wait, wait, wait, wait, wait, wait, wait, bleep, another flash, wait, wait, wait, wait, wait, bleep, another flash. Some species, the males actually give paired flashes, so they’ll fly along and then go bleep, bleep, wait, wait, wait, wait, wait, wait, wait. Bleep, bleep, wait, wait, wait, wait, wait. And so on. And so females who are kind of hanging around on grass down below can see these flashes, and they can recognize a male of their own species.

Narrator: But for all the romance and magic they add to our summer evenings, firefly populations around the globe are at serious risk. Those finely tuned mating rituals? Thanks to light pollution, those love letters get a little lost in translation.

Lewis: In areas where there’s a lot of bright lights, it’s been shown that it’s much, much more difficult for the male fireflies to find the females and for the females to see the flashes, the advertisement flashes of the male fireflies.

Narrator: And other threats like habitat loss and pesticide use have also put the population at risk.

Lewis: Sadly, in many parts of the world, there are other firefly species that aren’t doing so well. In fact, they are flickering out. And some of these fireflies are restricted to a very specific habitat. If that habitat goes away, the fireflies disappear. They can’t live anywhere else.

Narrator: It’s a story playing out all over the planet and across the animal kingdom. But as Lewis explains, education is absolutely key to conservation of fireflies and of all at-risk species.

Lewis: If fireflies disappeared, a lot of the world’s wonder would disappear with them. Would you wanna live in a world without fireflies? I would not.

Narrator: By increasing awareness of these risk factors, Lewis hopes to shine a little light on firefly conservation, ensuring that these little bugs will be able to dazzle us for years to come, giving future generations the chance to spend their summer nights trying to catch lightning in a bottle.

EDITOR’S NOTE: This video was originally published in August 2020.

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