Fireflies: Why they glow and everything you need to know about them

Fireflies are illuminated by a chemical reaction. We give you all the explanation in this article, plus additional information about them, images and GIFs.

What are fireflies?

Whether you call them fireflies(Lampyridae) or light bugs, these insects are neither flies nor true insects. Instead, they are beetles of the order Coleoptera, like ladybugs and rhinoceros beetles.

Where do fireflies live?

Fireflies are found all over the world, on every continent except Antarctica, and are incredibly diverse, with some 2,000 species of fireflies. There may be many species sharing a single habitat. In fact, probably when you have seen them at home you have looked at several species.

Fireflies lighting up.
Fireflies lighting up.
Why do fireflies glow?

In order to light up, fireflies produce a chemical reaction inside their bodies. This type of light production is called bioluminescence and is shared by many other organisms, mainly marine organisms.

Fireflies have light organs containing specialized cells under the abdomen.

In the cells, a chemical called luciferin is found and they produce an enzyme known as luciferase. To make light, luciferin combines with oxygen to form an inactive molecule called oxylciferin. Luciferase accelerates the reaction, which occurs in two steps:

  1. Luciferin combines with adenosine triphosphate (ATP), which is found in all cells, to form luciferyl adenylate and pyrophosphate (PPi) on the surface of the enzyme luciferase. Luciferyl adenylate remains bound to the enzyme: luciferin + ATP ————-> luciferyl adenylate + PPi
  2. Luciferyl adenylate combines with oxygen to form oxyluciferin and adenosine monophosphate (AMP). Light is emitted and oxylciferin and AMP are released from the enzyme surface: luciferyl adenylate + O2 ————-> oxylciferin + AMP + light

The light emitted by fireflies has a wavelength between 510 and 670 nanometers and can illuminate from pale yellow to reddish green.

In the cells that produce the light there are also uric acid crystals which help to reflect the light away from the abdomen.

Oxygen is delivered to the cells through a tube in the abdomen called the abdominal trachea.

Unlike a light bulb, which produces a lot of heat in addition to light, the light from a firefly is “cold light” without much energy being lost in the form of heat. This is necessary because if the light-producing organ of a firefly were to overheat, the firefly would not survive.

Fireflies can control the start and end of the chemical reaction, i.e. the start and stop of their light emission, when they add oxygen to the other chemicals needed to produce light.

When do fireflies glow?

Fireflies light up for a variety of reasons.

Defense mechanism:

The firefly’s striking style warns predators of the insect’s bitter taste. Although apparently some frogs don’t mind as they can eat so many fireflies until they themselves begin to glow.


Male fireflies also glow to indicate their desire for mates, and willing females attract males with their own flashes.

Each species of firefly has its own flicker pattern, but some females can mimic the patterns of other species. Males land next to them, only to be eaten alive.

Not all fireflies flash. While all fireflies light up in their larval forms, there are many species of fireflies that do not use light as an adult mating signal. Instead, these “dark” fireflies use odors in the air, such as pheromones, to communicate.

Larval stage:

Fireflies spend most of their lives in the larval stage. While not all adults emit light, all fireflies have glowing larvae. The armored, grub-like larvae are vicious predators, crawling and consuming slugs, snails and earthworms. They can spend up to two years in this larval stage before metamorphosing into adults. Adults can live only a couple of weeks, and most do not eat during this time, only mate, lay eggs and die.

What do fireflies eat?

It is likely that firefly larvae feed on different prey than adult fireflies. The larvae are believed to be carnivorous and live on smaller insects, snails and slugs. Adult fireflies can also live on other insects, as well as pollen and plants, but some species may not eat anything; their lifespan is a few weeks.


The largest fireflies are enormous. Female Lamprigera fireflies can grow to the size of your palm. They are much larger than their male counterparts and lack wings. Two large light organs in its abdomen produce its characteristic glow.

Firefly populations are threatened by light pollution. Exterior lights prevent fireflies from seeing each other’s flashes. Therefore, they have difficulty finding partners. Other potential threats include habitat loss, pesticide use and climate change. Turn off the lights at night during firefly season to protect these peculiar creatures.

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Acerca de Alejandra Galaz

Divulgadora de la Ciencia y productora de videos. Me apasiona conocer y compartir los últimos avances en la ciencia y tecnología en especial temas de medicina. Soy médico cirujano de profesión, pero mi verdadera vocación es curar y crear contenido educativo.

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