For two weeks each year at the beginning of summer, fireflies light up a portion of Great Smoky Mountains National Park. They glow in unison or in waves as males communicate with females in an elaborate mating dance that no one fully understands. There are at least 19 firefly species in the park, but Photinus carolinus is one of the only fireflies in America known to light in unison. Tourists arrive by the thousands to watch.
The weird, alien phenomenon of bioluminescence has always captivated us, especially before we understood what caused it. Aristotle wrote about glowing marine organisms. Huckleberry Finn and Tom Sawyer attempted to use a glowing fungus to light their way as they dug a tunnel. At about the same time, Jules Verne described the glowing “milky sea” effect in 20,000 Leagues Under the Sea.
Today scientists know quite a bit more about bioluminescence and the many forms it takes. For one thing, those fireflies we all know so well are actually one of the more uncommon forms of biological light. As much as 80 percent of all bioluminescent organisms live in the ocean. Those on land are typically insects, such as fireflies (also known as lightning bugs), or fungi, like the Brazilian “coconut flower” mushroom recently covered in Nature Conservancy magazine. (Read more stories from our December/January issue here.)
Panellus Stipticus displaying bioluminescence. Photo by Ylem / Wikimedia in the Public Domain
On land bioluminescence fascinates us and often works as an integral part of the organism’s reproduction. In the dark, fireflies recognize each other based on the pattern and type of light each emits. (Check out the “blue ghost” fireflies that emit a tinted light.) Fungi are believed to use their glow to attract nocturnal animals, which will then carry spores elsewhere. But, in the deep ocean, bioluminescence becomes even more critical for its organisms; there it’s the main source of light in a dark world.
“Understanding it is critical to understanding life in the ocean,” says biologist and self-described “bioluminescence junkie” Edith Widder in her popular TedTalk on the subject. Widder and her partners are responsible for some of the underwater technology that has helped scientists document and better understand the role of biological light in the ocean.
She explains that bioluminescence in the deep ocean can be used to attract mates and food, or can serve as a defense mechanism. Some organisms send light along the length of their bodies or even release clouds of light just as a squid releases ink. And that “milky sea” effect of Verne’s? Scientists aren’t positive what causes a portion of the ocean to sometimes light up so brightly it can be seen from satellites. But a common theory suggests that effect comes from enormous groupings of bacteria floating near the surface of the Indian Ocean…