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A Ghostly Green Light

by | Jul 26, 2021 | Nature, Wildlife | 0 comments

I wake in the early hours to a faint green light on my ceiling, no bigger than the tip of a matchstick. Curious, I climb out of bed, inch my way across the bedroom and fumble for the light switch. In an instant the magic is extinguished. Now all I see is a cellar spider with something in her web, which I gingerly remove while balancing barefoot on a wooden chest.

It’s a male glow-worm. With the exception of its glowing end, the glow-worm (which is really a beetle, not a worm) seems dead. Its dark brown body is dull, like its covered in dust, and as there’s no movement, I presume it must have been killed by the spider’s bite. But the glowing end gives me hope, so I place it in a jar on the off chance that it might revive by the morning.

Morning comes but the light in the jar on my desk is extinguished. I feel very saddened by this. Since 2001, the UK glow-worm population has fallen by three-quarters. Scientists believe the main reason is our changing climate, but I can’t help but wonder if pesticides and our obsession with ‘tidiness’ might be having a significant impact on their population, too. Adult glow-worms don’t eat, but their larvae predate snails and slugs, so slug pellets won’t be doing them any favours, and repeatedly cutting vegetation right back, especially with indiscriminate power tools such as strimmers, removes vital cover for glow-worms and their prey. That’s not to say that all cutting is bad – after all, female glow-worms might struggle to be seen if they can’t makes their way out of excessively dense vegetation, but as the UK Glow worm survey website points out, cuts at peak glow-worm time (June-August) should either be sensitively done or left until later in the year. Light pollution must also be having a detrimental effect on glow-worms. I like the dark, and during the long days of summer I find it unnecessary to have many lights on at all. But an increasing number of people light their homes and gardens up all night – eliminating not only darkness, but also any local male glow-worm’s chances of finding a female, as they will be attracted to the brighter, artificial lights, and overlook the ghostly-green lights of potential mates.

It’s said that glow-worms prefer areas rich in limestone, but they can be found in a wide variety of habitats, such as hedgerows, railways, cliffs, heathland, graveyards and gardens. I saw my first years ago on the grassland above Durdle Door in Dorset, but since then I’ve also seen them on a heathland at Brownsea Island, nestled in an ancient hedgerow on a midnight walk on the outskirts of Bridport (accompanied by classical music, which was being played in a nearby garden) and now here, every summer, in our East-Devon garden and the surrounding fields. We once even found one glowing in October next to our cellar door.

I’m no expert, but what I’ve gathered from the past seven years of living here is that glow-worms, like so many animals, require a mosaic of habitats to survive. We rarely cut our grass in the summer (or at all) but we do regularly walk through it, creating areas where the grass is naturally shorter, and we have a handful of vegetable patches, too. We never use strimmers (they are far too destructive) but we will occasionally cut areas back with hand tools. We have lots of brambles, thistles and nettles, all of which seem to provide good habitat for snails, and we never use pesticides. Also, as we live on an old dairy farm, there is an abundance of flint and stony areas (our front garden was once a milking parlour), which provide female glow-worms and their larvae ample places to hide during the day. It’s often next to such places that I find them on summer nights.

Before I found the glow-worm on my ceiling, I was unaware that male glow-worms were capable of bioluminescence. But I discovered a study by Martin Dale titled: ‘Some notes and observations on the bioluminescence exhibited by the larva of the Glow Worm (Lampyris noctiluca) in captivity’ in which Martin noticed that male glow worm pupae were more likely to glow than female pupae when disturbed, and that the adult males produced short flashes of bioluminescence at dusk, while flying and when threatened. He also noticed that the males became more animated around dusk, about fifteen minutes before the captive females began glowing.

Reading the study (which can be found here) made me feel more hopeful about the glow-worm I had rescued. Throughout the day, whenever I lifted the jar to inspect him, the disturbance caused him to glow, so I presumed he was inactive because it was the day, and come dusk he would liven up. But when dusk came there was no change. He was still producing a glow when I moved the jar but looked thoroughly paralysed.

Tipping him out into my hand it suddenly dawned on me that he looked duller than the photographs of glow-worms I’d seen on the internet, as if he was covered with something translucent. Using a dunnocks’s claw I had on my desk (that’s a story for another day) I gently began to scratch at his tail end and, to my delight, I saw it move. I scratched again and managed to lift the thinnest layer of spider’s silk up and off his glowing tail, which wiggled around wildly. I reached for some nail scissors, and between them and the dunnock’s claw I slowly and very carefully removed all the spider’s silk from the glow-worm. I was left with a lively little insect crawling all over my hand, so I raced outside and sat with him in the dusk. With his large black eyes and twitching antennae he was surprisingly cute, and he spent about a quarter of an hour exploring my hand. I could have allowed him to crawl onto a nearby hollyhock and gone back inside, but I wanted to make sure he could fly, so I waited. From the trees behind me I heard the first few begging calls of the local juvenile tawny owls, and as the sky slipped to a deeper, darker blue, moths started to flutter past me, followed by common pipistrelle bats, which I hoped my glow-worm would manage to avoid.

Eventually he lifted his elytra, the wing cases that protect his transparent hindwings, and off he flew. I was elated. I was so concerned that I might have damaged him when I removed the silk that seeing him fly off confidently was a huge relief. I walked back inside with a huge grin on my face.

About half an hour later, I absentmindedly switched on the bathroom light to brush my teeth, leaving the bathroom door ajar. The light shone straight to our front door, which has a window in it. I glanced out of the bathroom (which has no windows) and there, racing up the front door window, was a male glow-worm. Realising my mistake, I switched the light off and finished cleaning my teeth in the dark. A little later, I went on a glow-worm hunt around our garden and to my delight, I found a female glow-worm with a lively little male on her back.