What Makes Fireflies Light Up?

(Image credit: Cathy Keifer | Dreamstime)

The faint eerie glow of fireflies is a summer night staple, but the process that makes these insects light up is surprisingly sexy.

There are more than 2,000 species of fireflies, or lightning bugs, and they are actually winged beetles. Typically only seen in the summertime because they thrive in warm and tropical environments, a firefly's glowing mechanism serves several purposes thought its lifetime.

Fireflies glow even when they are just tiny larvae. The flashing of their pale, lime light acts as a warning to predators. Many firefly larvae contain chemicals that are distasteful or toxic to animals and humans, according to a study by Tufts University researchers.

So what makes them glow?

The light is a result of the mixing of oxygen, a pigment called luciferin, the enzyme luciferase, a chemical called adenosine triphosphate (ATP), which provides cells with energy, according to Harvard Medical School researchers. Uric acid crystals, located in the cells that are activated to make the light, act as a reflective layer and shine the light away from the bug's body.

However, the blinking patterns of the firefly's abdomen remain a mystery, as scientists are unsure of whether the patterns are controlled by the insect's nerve cells or oxygen supply.

But scientists do know what the flashes are used for: adult fireflies shine different intermittent signals to grab the attention of possible future mates. Flash patterns vary from short burst to a long continuous flashing sequence, and different firefly species have their own unique successions of light, making it easier for compatible mates to find each other.

Both male and female fireflies turn on their green lights when choosing a mate, and use their blinking lights as a means to communicate during courtship.

What about the myth that holding a firefly will eventually cause it to stop glowing because it has to fly in order to produce the energy it needs to make light?

"It is not true that they have to move to produce light," Steven Haddock, a scientist who studies bioluminescence at the Monterey Bay Aquarium Research Institute, told Life's Little Mysteries.

Besides fireflies, many other organisms, especially marine creatures, use bioluminescence for sexual selection, attracting prey and as a means of camouflage. It has been estimated that about 90 percent of deep-sea animals are bioluminescent, according to the Scripps Institution of Oceanography.

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Remy Melina was a staff writer for Live Science from 2010 to 2012. She holds a bachelor’s degree in Communication from Hofstra University where she graduated with honors.