Why Do Fireflies Light Up? - How Fireflies Glow

To better understand how fireflies glow, we can explore a little background on these insects. The following are some basic characteristics of fireflies:

• They to the order Coleoptera and to the family Lampyridae.
• Despite their common name, fireflies are actually a type of beetle.
• There are about 2,000 species of firefly.
• They are between 5 and 25 mm in length.
• Their body is soft and flattened.
• They are normally brownish-black or black in color and usually have yellow or orange markings.
• In general, both females and males have wings.
• In some species only one sex has a light-producing organ.
• Some species have larvae that are also luminescent.

Now we know a little background about them, why do fireflies light up? The ability of a firefly to glow comes from bioluminescence. Generally speaking, this is a biochemical process. Fireflies appear to have initiated this ability in the larval stage, one of the reasons they are often known as glowworms. It is believed the reason for this is to warn predators of their bitter taste when eaten so they will avoid doing so. In this way, glowing is a defense mechanism.

This defense mechanism of fireflies doesn't always work. There are examples of frogs which will eat so many fireflies that the frog themselves will glow. It is believed that during evolutionary process and adaptations, the adult fireflies also developed this ability to light up.

While glowworms (the larval stage of fireflies) will glow for protection, adults have also adapted their use of bioluminescence. The reasons adult fireflies glow is linked to reproduction. Fireflies can flash their bioluminescent bodies to create signals. This allows males and females to differentiate themselves and choose the correct partner for reproduction.

Discover more about diurnal and nocturnal insects with our comparison of the differences between butterflies and moths.

Fireflies emit a mostly cool light with a very low amount of heat. The type of light that fireflies emit is only in the visible spectrum, with a wavelength ranging from 510 to 670 nanometers. The entire process occurs due to control by their nervous system using special organs rich in photocytes. These are cells abundant in air tubes known as ‘tracheas’ which are common in insects.

These specialized structures are usually located in the lower abdomen of these animals. The chemical process is enzymatic and happens thanks to an enzyme known as luciferase, which acts on a compound called luciferin which typical in this type of animal.

This compound reacts with other chemical compounds to release energy in the form of light. Such compounds include magnesium, adenosine triphosphate (ATP) and oxygen. Using the abdominal trachea, the firefly absorbs oxygen and combines it with luciferin (and the rest of the compounds) to produce and emit light.

We said that each species of firefly has differences in terms of the way it emits light, which is why there are variations. Such differences can be seen in the duration of luminescence, the number of repetitions, the shape of their wings and the color of the light. Fireflies can glow yellow, green or red. If fireflies are seen from afar, we will eventually see a different color than the one they actually emit.

Different animals use bioluminescence in different ways. Discover more with our article on different animals that can change color.

You may wonder if fireflies produce light year round, but this depends on each species. It is important to know there are species within the genus Coleoptera that do not produce light, although the majority of them do. These are usually of diurnal habits. They mainly rely on chemical communication with the use of pheromones for mating.

The fireflies that do produce light are nocturnal. These are the species of firefly that use bioluminescence to see each other. Depending on the species, some are active year-round. Others are only temporary or seasonal. Let's see some examples:

• In Asia, in countries like Malaysia, Thailand, the Philippines and Hong Kong, there are fireflies of the genus Pteroptyx that can be seen practically all year round. In fact, its observation has become a tourist attraction because it produces a beautiful landscape where trees with hundreds of glowing fireflies can be seen. Unfortunately, a decrease in such sights has been reported due to the deforestation of certain areas.
  
  
• Something similar in relation to tourist visits occurs in Tennessee, United States, in the Great Smoky Mountains National Park. Many people come to see the fireflies of the Photinus carolinus species, but this time only at the beginning of June which is when they come out to light up.
  
  
• In Spain, the most common species are the Mediterranean firefly (Nyctophila reichii) and the Iberian firefly (Lampyris ibérica). Both are seasonal and begin to shine between May and June until the end of July, like the rest of the species, in mainly humid habitats.

Fireflies are one of those rarities in the animal world that are worth continuing to see, but their existence is under threat. To help conservation of fireflies, it is essential to stop the deforestation of natural spaces and minimize the use of agrochemicals that have a significant impact on insects.

If this information about why fireflies glow has been curious to you, don't miss this our related article which details what animals can glow in the dark.

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