Few insects vie in popular fame with the glow-worm, that curious little animal which, to celebrate the little joys of life, kindles a beacon at its tail-end. Who does not know it, at least by name? Who has not seen it roam amid the grass, like a spark fallen from the moon at its full?
- from The Insect World of J. Henri Fabre, an anthology of Jean-Henri Fabre's works translated from French by Alexander Teixeira de Mattos.
Glow-worms, also called fireflies or lightening bugs (I prefer to call them fireflies), don't live where I do, so I've never seen one. My only encounters have been in fictional accounts, but I can understand how they capture people's imagination – I'd be captivated if glowing beetles 'like a spark fallen from the moon at its full' were flying around my backyard. I suspect I'd watch them for hours, and back when I was a kid, I would have loved to catch them. According to the Smithsonian Institution's Animal; the Definitive Visual Guide to the World's Wildlife, 2000 species of fireflies exist world-wide, ranging in size from 0.5 to 3 cm. And it's no surprise that they're typically nocturnal; what would be the point of glowing if no one could see?
Their light serves different purposes through a firefly's life. As larvae, they flash to warn predators of the larvae's toxicity. As adults, each species emits their own unique set of flashes to attract mates. Males typically can fly around to find their mate, while the flightless females stay in one place and flash. A female firefly's flashing can be the downfall of a male, since some females mimic other firefly species' flashes to earn themselves a quick meal.
A firefly's light falls into the 510 – 670 nm range, corresponding to yellow, green or pale-red and contains no infrared or ultraviolet wavelengths. They produce their light purely through a chemical reaction that triggers a light-emitting pigment to flash within specialized cells in the firefly's abdomen.
Firefly populations are decreasing. Loss of habitat makes life harder for fireflies, and light pollution may be interfering with their signals. In fact, light pollution causes all sorts of havoc for critters. For fireflies finding a mate becomes more difficult, because how can they home in on a series of flashes from a potential mate while lights are flashing all around them? For other animals excess light confuses their sense of navigation, like puffins in Iceland disorientated by city lights. Children rescue the puffins and release them – which strikes me as a bit odd since puffin is considered a delicacy there. Light pollution is such an issue (probably more because it make the stars hard to see than what it does to critters) that there is an 'International Dark-Sky Association' and places designated 'dark-sky preserves'. I wonder what all the excess artificial light is doing to us?
Lots more info about fireflies can be found here.