Fireflies produce a chemical reaction inside their bodies that allows them to light up. This type of light production is called bioluminescence.
The method by which fireflies produce light is perhaps the best known example of bioluminescence. When oxygen combines with calcium, adenosine triphosphate ATP and the chemical luciferin in the presence of luciferase, a bioluminescent enzyme, light is produced. Unlike a light bulb, which produces a lot of heat in addition to light, a firefly's light is "cold light" without a lot of energy being lost as heat. This is necessary because if a firefly's light-producing organ got as hot as a light bulb, the firefly would not survive the experience.
A firefly controls the beginning and end of the chemical reaction, and thus the start and stop of its light emission, by adding oxygen to the other chemicals needed to produce light. This happens in the insect's light organ. When oxygen is available, the light organ lights up, and when it is not available, the light goes out. Insects do not have lungs, but instead transport oxygen from outside the body to the interior cells within through a complex series of successively smaller tubes known as tracheoles.
For a long time it was a mystery as to how some firefly species manage such a high flash rate, considering the relatively slow speed of the muscles that control oxygen transport. Researchers fairly recently learned that nitric oxide gas the same gas that is produced by taking the drug Viagra plays a critical role in firefly flash control. In this situation, oxygen that enters the light organ is bound to the surface of the cell's energy-producing organelles, called the mitrochondria, and is thereby not available for transport further within the light organ.
Female fireflies hang out on a tree branch or in the grass while the males fly around showing off their best flashes. When a female recognizes the flash from a male of the same species, she will answer with her best flash. Another reason that fireflies glow is to avoid predators. Fireflies are filled with a nasty-tasting chemical called lucibufagens, and after a predator gets a mouthful, it quickly learns to associate the firefly's glow with this bad taste! So not only does the flashing help attract a mate, it also warns predators to stay away.
One species of firefly that can't make its own lucibufagens acquires it by eating others that can. To lure victims, these fireflies mimic the flashing pattern of another species. Another reason that fireflies glow is to avoid predators. Fireflies are filled with a nasty-tasting chemical called lucibufagens, and after a predator gets a mouthful, it quickly learns to associate the firefly's glow with this bad taste!
So not only does the flashing help attract a mate, it also warns predators to stay away. One species of firefly that can't make its own lucibufagens acquires it by eating others that can. To lure victims, these fireflies mimic the flashing pattern of another species. When the unsuspecting male approaches to find a mate, he instead becomes a tasty treat to the tricky firefly. This video from Brigham Young University offers a quick glimpse of these remarkable insects that make their own light.
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