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.

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