As anyone who has seen a firefly knows, some living organisms are capable of producing and emitting light from within their own bodies. This is known as bioluminescence. Unlike many other common sources of light, bioluminescence creates light but does not generate very much heat. This means bioluminescent organisms can generate light without significantly affecting their own body temperature, or the temperature of their environment.
Bioluminescent organisms exist both on land and in the sea. Perhaps the best known glowing land organism is the firefly. The adult firefly can be seen at night, flashing during flight, but the larva of the firefly also glows. In fact, the larva of many flies and beetles are bioluminescent, and are often called glow worms.
On land, bioluminescence can also be found in some insect and worm varieties. Some varieties of centipede, known collectively as fire centipedes, are also bioluminescent. Some species of fungi and bacteria exhibit bioluminescence, as well.
Most examples of bioluminescence are found in the sea. Jellyfish, squid, and some crustaceans, including shrimp and krill, are bioluminescent, as are some fish, including anglerfish, the gulper eel, and the flashlight fish. Most of these organisms live at darker ocean depths that receive very little sunlight.
Dinoflagellates are single-celled organisms found in water that will glow when the water around them is disturbed, or when they are disturbed by predators. Vessels at sea often leave a trail of glowing dinoflagellates in their wake, making it possible to detect their presence at night.
Advantages of Bioluminescence
Evolution tends to preserve those biological traits that provide survival benefits to an organism. In what ways does bioluminescence help an organism to survive? There are several theories.
• Attraction - some fish use bioluminescence to attract prey, while the firefly uses it to attract a mate.
• Defense or Warning - some marine life can release a cloud of bioluminescent material to confuse an attacker and hide their escape, much as some squid release ink. On land, the glow of some larvae may be a warning to potential predators not to attack, as these larvae contain chemicals which are harmful to their attacker.
• Camouflage - in the ocean, some creatures glow in such a way that they look like the sunlight that filters down from the surface.
• Illumination - some creatures may use bioluminescence simply to help them see, especially in the depths of the ocean.
Because it has evolved in so many different environments and serves several different uses, it is likely that bioluminescence evolved independently in many different species. While human beings get by without bioluminescence, evolution suggests that bioluminescence is a very advantageous trait for an organism to posses.
Haddock, S.H.D.; McDougall, C.M.; Case, J.F. "The Bioluminescence Web Page", http://lifesci.ucsb.edu/~biolum/
Marc Branham, "Bioluminescence", http://hymfiles.biosci.ohio-state.edu/projects/FFiles/biolum.html
Wikipedia, "Bioluminescence", http://en.wikipedia.org/wiki/Bioluminescence