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Fireflies are a group of glowing insects that emit a bright glow.

Many people appreciate their strange ethereal beauty, but there is a lot of misunderstanding and confusion about what this insect actually is. First off, the name itself is a huge misnomer. It's not really a worm at all. Instead, "firefly" is a catch-all term that describes larvae (similar to worms) with glowing bodies. To add to the confusion, several insects, including larval and adult stages, are also known as fireflies.

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The ability to produce light by entirely organic means is known as bioluminescence. Luminescence is usually intended to attract mates, capture prey, or warn predators. If you spot a glowing insect, it's almost certainly a beetle (although some small insects can also glow). This article will discuss many different types of fireflies, including both larvae and adults of certain species.

Lampyris noctiluca common firefly from Europe isolated on white background.
Several insects, including larval and adult stages, are known as fireflies.

©Piotr Velixar/Shutterstock.com

3 Incredible Firefly Facts!

  • In some species, only females are capable of bioluminescence. This usually indicates that it is used for reproductive purposes only.
  • A fungal gnat that lives in damp caves in New Zealand has the remarkable ability to produce glowing slime tubes in its larval form. These slime tubes, about 16 inches long, hang from the cave ceiling and contain tiny silk threads that emerge from the larvae's mouth. While other insects are attracted by the light from the tube, they accidentally get stuck on the silk thread, making a tasty meal for the larvae. Adult fungal gnats, which live only a few days, also glow, but it's not clear what effect this has. It may just be a leftover feature of the larval stage.
  • The organs responsible for producing light vary so widely in size, location and structure that they may have different evolutionary origins.
In some species, only females are capable of bioluminescence.

Scientific name and evolution

As mentioned earlier, "firefly" is a somewhat confusing catch-all term. While there are several species of insects and/or larvae known as fireflies, it's not really a scientific term and doesn't quite fit any taxonomic classification. "Firefly" can refer to many different species, some of which are only loosely related to each other or not related at all. The only thing they have in common between them is their ability to bioluminescent.

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Firefly larvae, Firefly, glowing on a green leaf.
While there are several species of insects and/or larvae known as fireflies, it's not really a scientific term and doesn't quite fit any taxonomic classification.

© Karelian/Shutterstock.com

Types and Evolution

Bioluminescence in animals, including marine animals, has evolved in different ways and for different purposes. Some lighting functions to attract mates, some to help capture prey.

Fireflies generally fall into two main groups: They are either beetles or fungal gnats. The glowing insects most people are familiar with, including fireflies, true fireflies, and lightning bugs, belong to the family of beetles known as Pyrophoridae (although in fireflies, it is mainly the larvae known as fireflies). Another closely related family, Phengodidae, also contains many species called fireflies. Fungal gnats, by contrast, are nothing like beetles. They are more closely related to flies in the order Diptera. From an evolutionary perspective, their bioluminescent adaptations evolved separately from those of beetles.

firefly beetle

  • Clicker Beetles – Beetles of the Elateridae family of beetles are able to make a clicking sound from a spine on their body, which actually launches them into the air. There are approximately 10,000 different species of these beetles.
  • Firefly Beetles – Beetles of the family Phengodidae are commonly known as firefly beetles. Males are much smaller than their brethren, are not believed to eat, and have a shorter lifespan. However, females prey on other insects in the soil.
  • True Fireflies – The family of fireflies includes thousands of different species, including fireflies, lightning bugs, and other fireflies that typically glow at dusk.
  • Fireflies in the Rhagophthalmidae familyThe Rhagophthalmidae beetle family is still debated in terms of its taxonomy. It was previously thought to belong to the family Phengodidae .

firefly fungus gnat

These fireflies have a completely different method of using lighting to catch food. They are able to produce and drop sticky webs from their bodies on cave roofs. The lighting abilities of the fungal gnats are believed to have evolved separately in each of the three groups.

  • Keroplatus – This genus is found in Eurasia. They feed only on fungal spores.
  • Arachnocampa – This genus contains five subspecies and is found in Australia and New Zealand.
  • Orfelia – This genus also feeds on fungal spores and has only one subspecies, found in North America.
As for the different types of fireflies, the only thing they have in common between them is their ability to bioluminescent.

© Timo Newton-Syms/Creative Commons

Appearance: How to Identify

These insects vary widely in size and appearance. Each genre seems to have its own unusual quirks and strange facts. Bioluminescence is a common feature among them. This light can be emitted as a series of flashes or as a continuous glow in colors ranging from green, yellow, orange and blue. Bioluminescence is produced by chemical reactions involving luminescent pigments. The nature of this chemical reaction varies from group to group.

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As mentioned earlier, fireflies generally refer to the larval stage of glowing insects. But there are also entire species that have received the firefly name. The common European firefly (a long, narrow beetle in the family Pyrophoridae) is one of the best-known examples.

Unlike the closely related fireflies, only the females of this species are actually able to glow, at least as adults. She is a larval, which means she retains many larval characteristics as an adult and therefore lacks wings. When the mating season arrives around June or July, she climbs a plant and constantly flashes bright lights to attract one of the winged males. His large photosensitive eyes can see light from up to 50 yards away. The brightness itself is an indication of the number of eggs she is carrying. So a male half her size will try to mate with the brightest female.

Habitat: Where to Find Them

These insects are found in many different environments around the world. Depending on the species, their habitats include forests, grasslands, meadows, and even gardens. In contrast, fireflies, the larvae of fungal gnats, are mostly found in burrows or caves.

Diet: what do they eat?

Most of these insects are actually carnivorous. Even species that use bioluminescence primarily for reproductive purposes tend to eat meat.

what to eat

These insects provide a steady food source for many different birds, mammals, reptiles, amphibians, spiders and other insects. There are almost too many predators to even be named.

what do they eat

Many of these insects tend to be predatory in nature, and their feeding patterns can be quite scary. As previously mentioned, fungal gnats use their bioluminescence to trap their prey in filamentous threads. Some people also live up to their reputation by eating fungi.

In contrast, the larvae of the common European firefly inject toxic digestive fluids into their prey, usually slugs and snails. This fluid gradually paralyzes and liquefies its victim, allowing the larva to lick the carcass effortlessly and easily. Because the prey is usually several times larger than the actual larva, it provides a good meal.

A beetle larva needs to be a voracious eater because once it becomes an adult it lives off its fat reserves and eats next to nothing. Once it reproduces, it has actually reached the end of its life cycle.

Most of these insects are actually carnivorous. Even species that use bioluminescence primarily for reproductive purposes tend to eat meat.

© Jasja Dekker / Creative Commons

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about the author

heather ross

Heather Ross is a middle school English teacher and mother of 2 people, 2 tuxedo cats and a golden doodle. In between taking the kids to soccer practice and grading homework, she loves reading and writing about all things animals!

Firefly FAQs (Frequently Asked Questions)

Are fireflies herbivores, carnivores, or omnivores?

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Fireflies are omnivores, which means they eat both plants and other animals.

To which kingdom do fireflies belong?

Fireflies belong to the animal kingdom.

What phylum do fireflies belong to?

Fireflies belong to the phylum Arthropoda.

Which category do fireflies belong to?

Fireflies belong to the class Insecta.

What family do fireflies belong to?

Fireflies belong to the firefly family.

What order do fireflies belong to?

Fireflies belong to the order Coleoptera.

What type of mulch do Glow Worms have?

Fireflies are covered in shells.

Where do fireflies live?

Fireflies are found all over the world.

What type of habitat do fireflies live in?

Glowworms live in undisturbed woodlands and caves.

What is the main prey of fireflies?

Fireflies prey on snails, slugs and insects.

Who are the natural enemies of fireflies?

Natural enemies of fireflies include spiders, birds, and centipedes.

How many babies does a firefly have?

The average number of larvae in a firefly is 75.

Any interesting facts about fireflies?

Spot glowworms inhabiting lush woodlands and caves!

How many kinds of fireflies are there?

There are 12 species of fireflies.

What are fireflies?

Fireflies can be defined as larvae (and sometimes adult insects) that exhibit bioluminescence. They fall into two main groups: beetles and fungal gnats. Scientists believe that their ability to bioluminescence evolved multiple times over millions of years, given the wide variation in the organs that produce the light. There are so many different facts about warm light that it's hard to generalize them all.

Are Fireflies Dangerous?

Fireflies do not pose any danger to humans. Even the toxin-producing larvae only use them on their prey. They do not affect humans.

How many legs does a firefly have?

Like all insects, fireflies have six legs.

How to identify fireflies?

All fireflies can be identified by bioluminescence. Otherwise, they look almost identical to any other type of insect. Many of them have long, narrow bodies and wings that allow them to fly.

What will the firefly become?

Like any other type of insect, bioluminescent larvae obviously progress to the adult stage, at which point they may lose their ability to glow or keep it glowing for life. Species that use light to catch prey are more likely to lose it as adults, or for it to simply become a vestigial trait. Species that use the light for reproductive purposes or for warning apparently keep it into adulthood.

Where did you find fireflies?

Fireflies are everywhere on earth. Since many of them like to live near gardens, hedges, meadows, and similar habitats, they often live in close proximity to people.

Are fireflies rare?

Fireflies can be found almost everywhere.

What eats fireflies?

Fireflies are eaten by a variety of other animals, including birds, mammals, reptiles, amphibians, spiders and other insects.

Are fireflies poisonous to humans?

No, fireflies are not poisonous to humans, but some species release a poison that immobilizes their prey.

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  1. Encyclopedia Britannica, available here: https://www.britannica.com/animal/glowworm
  2. Wildlife Trust, available here: https://www.wildlifetrusts.org/wildlife-explorer/invertebrates/beetles/glow-worm
  3. New Scientist, available here: https://www.newscientist.com/article/2116354-cave-glow-worms-vomit-long-sticky-urine-threads-to-catch-prey/