Posted: Wednesday 15 August 2012
by Richard Jones

The marvel of glow-worms, and their New World equivalents the fire-flies, has entered popular mythology. Is it any wonder?

Glow worm in the palm of a hand

On Saturday evening I stood in the blackness of the field just north of our Dordogne gite and looked up at the sky. I was looking for Perseids, the August meteors left by the trailing remains of the Swift-Tuttle comet, which last passed by Earth's orbit in 1992. But there were some high whispy clouds, visibility wasn't very good, and I saw no shooting stars. I did, however, find a glow-in-the-dark fairy.

The marvel of glow-worms, and their New World equivalents the fire-flies, has entered popular mythology. Is it any wonder? The otherworldly glow cupped in my hand fascinates me still, just as it did when I first saw them, as a young teenager, deep in the woods of the Sussex Weald.

Part of my excitement is the geek chemical knowledge that glow-worm light is the exact opposite of photosynthesis. Where the light photon was trapped by chlorophyll (the green pigment in plants), releasing one electron and empowering the cascade of reactions eventually leading to the creation of living organisms' "universal" energy storage molecule adenosine triphosphate (ATP), in the glow-worm the reverse reaction occurs and ATP gives up its electron to cascade energy the other way through a series of elegant intermediary compounds, eventually liberating a light photon into the dark night sky. This light is 'cold', a pure chemical light, with none of the wasteful heat energy given up in electric or candle light.

The insect's eerie glow was visible in the grass from several metres away. She was on her own, though I searched about quite carefully after my earlier meteor-free disappointment. The female glow-worm verily lives up to her name, and despite being, technically, a beetle, her lack of membraneous flight wings and hard wing-cases makes her much more worm-like than her conventionally beetle-styled mate. Male glow-worms can, and do, fly and home in on the particular wavelength of the female's light -- a very useful mate-finding strategy.

I'm not entirely sure, this being the much more highly biodiverse European mainland, but I think this is the same species as we find in the UK, Lampyris noctiluca. I need to try and find some males now. I shall be continuing my Perseid watch through the week, as atmospheric conditions allow. But as well as gazing towards the heavens for shooting-star streaks of fire, I will also be looking Earthwards, for tiny glowing grass stars.

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Talkback: Glow-worms
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Adam Pasco 19/08/2012 at 21:55

Now that's one creature I've never had the pleasure of discovering. How exciting. I've stood for many an hour in the past looking upwards in the hope of seeing a shooting star around this time – I think the peak was meant to have been last weekend.

Richard Jones 19/08/2012 at 22:15

Just back now from the Dordogne. I didn't see any more glow-worms. And, eventually the next night, just a single meteor, even thought the heavens were clear and the Milky Way looked solid enough to reach out and touch.

Shrinking Violet 19/08/2012 at 22:35

I've never seen a glow-worm, either.  But my mother, who spent much of her youth in what was then rural Kent, spoke often of collecting them with my great aunt, and putting them on the rims of their hats to light the way home!  I suspect a degree or so of exaggeration here - but it's a fine story, nonetheless.

Joe_the_Gardener 20/08/2012 at 06:11

It seems that glow-worms are in serious decline, probably due to habitat loss and pesticides, but maybe for other reasons. They prefer rough grass, and road verges were always a good place to see them. When some friends bought a house in France 20 years ago, our night walks would find thousands of them. Now it's down to just a few. Is it because the roadsides and ditches are now mercilessly mowed or are there other reasons? 

We need many more people to survey them in Britain to try to establish some baseline data, so if you've nothing better to do on warm nights in July, resolve to get out and look for them next year, and report your results to your local Wildlife Trust.

Bookertoo 20/08/2012 at 20:21

Used to see them in my long ago youth, but it is right that it has been many years since I saw one last.  What a shame, they were a delight to us as children. 

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