Along the tidal rivers of Southeast Asia, thousands of male fireflies gather in trees at dusk and flash their bioluminescent lights in an attempt to attract the female of the species. At first, their blinking is uncoordinated, but as darkness deepens they begin to flash in unison. Soon, entire trees full of fireflies pulse like flickering fires.
The females, from far off, see the pulsating lights. They come. They mate in the cold incandescence of a winking tree.
As the glowworm love song says, when you gotta glow, you gotta glow. Everywhere, from the riverbanks of Southeast Asia to the inky depths of the oceans, nature glows with self-lit lights.
Certain toadstools can be seen from far off by their own shining. The lips of the megamouth shark are lined with hundreds of tiny lights that twinkle like a fairground's string of bulbs, enticing plankton into the gaping maw. Some starfish, if threatened, shed a glowing arm to distract the attacker, then flee in darkness to grow another.
Not so long ago, scientists believed self-luminescence was rare in nature. Now we know that living lights are common, especially in the sea. In very deep water, perhaps as many as 90 percent of creatures are luminescent.
The female marine fireworm releases her eggs in a luminous secretion for the male to find and fertilize. The angler fish of the dark abyss dangles a lighted wormlike appendage in front of its mouth and waits for an unwary prey to take the bait. Certain species of surface-swimming squids emit light from their undersides that mimics sky-glow, the better to hide from predators below.
Sex, predation, defense: The uses of light by living organisms are wonderfully diverse. Behind them all is a bit a basic chemistry. Proteins combine with oxygen to jack up the energy of molecules; when the molecules return to their original lower energy, they emit photons of light. The process is facilitated by an enzyme called luciferase. Luciferase makes the glowworm glow.
Recently, biologists have begun harnessing the firefly's blinking tail light to make things glow that never glowed before. More tomorrow.