Guest blog written by Robin Scagell, UK Glow Worm Survey, June 2022

Everyone has heard of glow worms but most have never seen one. They are actually quite widespread and many people would be surprised to find that they could probably see them quite close to their homes, if they knew where to look. Glow worms favour poor soils, so they are common in chalky areas, but there are calcareous parts of Wiltshire where they seem to be absent. Is this a genuine lack or just because of under-reporting? We’d like to know.

They are also found in glades in ancient woodland so I was surprised to notice a few years ago that there had never been any reports of them from Savernake Forest. Accordingly a search party set out and found them along some of the rides. Quite possibly there are many more. As the distribution map shows, there are large parts of Salisbury Plain, even away from the obvious MoD areas, where we’d expect to see them, yet there are few reports.

Map of sightings

Image caption: Where glow worms have been seen in Wilts, mostly in the past five years, from iRecord. Base map from Topomap.

What to look for

Glow worms are beetles, and it’s the wingless female that glows from the underside of her abdomen. The glow is a chemical reaction rather like that in the glow sticks that you get at night-time festivals. It’s surprisingly bright and under good conditions you can see it from 50 metres away. She glows to attract the males, which can fly. When one turns up she turns off her glow and disappears down into the undergrowth where she will lay her eggs. So the glowing females you see are all unmated ones, and you may need to be there at just the right time to see one. 

Photo of a glow worm

Image caption: An adult female glow worm in typical pose, clinging to a grass stem in chalk grassland. Credit: Robin Scagell.

The glowing season runs from early June through to the end of July, and sometimes later. They start to appear when it is dark enough that you can no longer see colour in the landscape by ambient light, usually after 10:30 pm. They glow for up to two hours each night. 

You can find out much more at the glow worm website, www.glowworms.org.uk.

Should you see glow worms, please do send in a report via the special iRecord glow-worm reporting form on the website, or use the iRecord app, but if you do that please tell us the number seen and the time.

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