ISLAND CONSERVATION-Magic of the firefly |15 October 2007

by Pat Matyot

We leaned against the trunk of a bwa rouz in a patch of forest above Le Niol and breathed in the night breeze, relishing its leafy tang. The nearby stream gurgled through crevices among the granite boulders. The sound it made mingled with the faint strums of reggae emanating from somewhere in the distance.

Something floated across my field of vision. My friend Xavier had seen it too. He looked up, startled. It was a tiny flashing light. It drifted past, pulsating rhythmically, like a miniature UFO from a science fiction film. “A firefly!” he exclaimed. “Just the thing to complete a lovely night like this!”

I knew what he meant. My own fascination with the mousfe, as the firefly is called in Creole, had started when I was still a child. My father brought one home in a matchbox one evening and released it inside the house after switching off all the lights. I remember staring in rapture as the insect hovered about the ceiling, flashing frantically. I marvelled at the idea that an animal could give out light like an electric bulb.

Later, I realised that the firefly is actually a beetle, and not a fly at all – in other words, it is more closely related to ladybirds and rhinoceros beetles than to, say, the housefly. Like with other beetles, the delicate gauzy hind wings – the ones used for flying - are covered and protected by the thickened fore wings or wing covers. The banal appearance of the insect belies its unusual ability: about one centimetre long, it is entirely black except for the thorax (between the head and the abdomen) and the lower surface of the body, which are orange, and a whitish patch under the tip of the abdomen. This patch is the light-producing organ. It is larger in the male than in the female. The light given out by the male is therefore more powerful than that of the female.

After more than a century of painstaking research, starting in 1885 with the French physiologist Raphaël Dubois, scientists have fathomed out quite a few of the secrets of firefly light. They have discovered that the pulsating glow that has stirred the imagination of poets across the ages is actually produced when a substance called luciferin in special cells combines with oxygen breathed in by the firefly. Energy for the chemical reaction is supplied by adenosine triphosphate or ATP (the “energy currency” in all life forms), while the enzyme luciferase facilitates the process. This complicated chemistry is controlled by the nervous system of the insect. Behind the light-producing cells there is a reflecting layer of cells containing a white substance, apparently ammonium urate.

The light appears to our eyes as greenish yellow. It is around 98 per cent “cold light”, with almost no heat produced as a by-product – very different from what is given out by an ordinary electric light bulb, which contains a lot of wasted energy in the form of heat (as much as 90 per cent with cheaper models!).

But what, you may ask, is the purpose of the firefly’s flashes of light? We now know that they are used for sexual communication. Males and females respond to each other’s signals by sending out answering blinks – a sophisticated form of flirting to pave the way for mating.

But a firefly’s tail-light will also glow brightly when the insect is under stress – caught in a spider’s web, for instance. Naturalist Guy Lionnet even tells of how a firefly that has been swallowed by a house gecko can be seen flashing its light for some time through the gecko’s semi-transparent body!

Scientific research has not succeeded in demystifying the mousfe (luciole in French). The sight of one inevitably awakens the poet inside us. At Le Niol, as we watched the firefly disappear behind a low bush, Xavier stretched out his arms and murmured: “A falling star!”

Fortunately I was there to share the moment with him. Over two and a half centuries ago the Japanese haiku master Tan Taigi (1709-1771) wrote:

tobu hotaru
areto yuwan mo
hitori kana

A firefly flitted by:
"Look!" I almost said,
But I was alone.

(The Island Conservation Society promotes the conservation and restoration of island ecosystems).