I can see them hovering in my Brooklyn yard: tiny balls of yellow light that flicker on and off in the dusk like lighters at a rock concert.
Fireflies are quite a common sight, although for how long we don't know. There have been widespread reports that firefly numbers are dwindling. The reports are all anecdotal, but they were enough of a concern for entomologists and biologists to hold a symposium in Thailand in 2008 entitled, "Diversity and Conservation of Fireflies." If fireflies are under threat, it's a terrible state of affairs.
Fireflies belong to a very exclusive group of land creatures that exhibit a phenomenon known as bioluminescence.
In simple terms, bioluminescence is technique certain organisms have developed to create energy, in the form of light, through a chemical reaction. This reaction often involves a chemical called luciferin.
Fireflies are unique because most bioluminescent creatures – 80% – live in the sea. On land only certain insects and fungi are bioluminescent.
It was in the ocean that I first found out about this phenomenon.
I grew up in England where we don't get fireflies. We get things called glow-worms, which are not worms at all but flightless insects. They're hard to spot because they're usually hidden away in long grass or hedgerows. Consequently most Brits will probably tell you that their only recollection of a glow-worm growing up was via the pages of a cute children's story.
It was a few years ago and I was on Lombok, a tiny island next to Bali, when I first experienced the weird spectacle of nature flickering to light in the darkness. I went for a midnight swim and started to feel a strange prickling sensation and when I dipped my head underwater and ran my hand in front of me it was as if the Milky Way had been miniaturized and liquified at the same time.
The trail of sparks left by your moving hand in bioluminescent waters is caused by single-cell organisms called dinoflagellates. They're a mysterious organism scientists don't fully understand. They're a form of plankton and while they feed on prey and move around like animals, they can also convert the sun's rays into food using chlorophyll in the same way plants do.
If you want to see the coolest bioluminescent creatures, though, you've got to go into deep water.
Unless you're James Cameron or that couple who got wed on the deck of the wreck of the Titanic, you probably can't afford a ride in a deep-sea submersible to the ocean bottom.
Don't despair, though. If you're lucky enough to be in the American Museum of Natural History anytime soon you can check out their wonderful exhibition, “Creatures of Light: Nature's Bioluminescence,” which runs until January 6, 2013.
Here, fireflies rub shoulders with the creatures of the deep. In total, 80% of deep-sea organisms are bioluminescent, and certain of them have developed fascinating and elaborate ways of illuminating the permanent night.
Anglerfish, which are frankly hideous looking things, get their name from the modified spine that sticks out of the forehead like a fishing rod. The rod is topped with a lure that pulses with bacterial light.
Like most deep-sea creatures, anglerfish emit blue light because it's easier to detect at these depths. An exception is the stoplight loosejaw dragonfish, which gives off red light from indents just below its eyes. The loosejaw gets its name from the fact that its jaw can dislocate from its mouth when it's hunting prey. Consequently it looks quite a lot like the alien in "Predator" (which I watched as a child when I'd grown out of the cute glow-worm stories).
The natural history museum exhibit contains many more highlights, including a small replica of a cave in New Zealand where thousands of fly larvae have turned the ceiling into a festival of stars.
Walking around the exhibit I was reminded of the limitless capacity nature has to amaze. If you're in New York and you have a spare afternoon, go see it. Failing that, take a look in your backyard.