There’s a species of summer magic I chase every year. It’s small, fierce and insistently beautiful and your best chance of seeing it is on hot nights in June and July. Tonight I’m searching for it in a disused chalk quarry on the outskirts of Cambridge, an eerie, lunar landscape of towering white cliffs and patches of bare ground resembling snowfields strewn with bones.
This is a nature reserve – one of only three UK sites where moon carrots grow – and it is brimming with life. Green longhorn moths the colour of stained gold velvet decorate pale scabious flowers; rabbits graze in drifts of trefoil, kidney vetch and thyme. The evening air is full of huge beetles with handlebar antennae, hooked feet and wildly erratic flight: cockchafers. I feel small, insistent tugs as they get entangled in my hair and impatiently comb them free with my fingers. I’ve not come here for them. I’m waiting for something else and it’s nearly time.
With a little thrill of anticipation I see that the light is fading fast. By 10.30pm, the last snowy glow has faded from the cliffs, replaced by thin starlight and a soft, mothy blackness. And then the magic begins. Twenty feet away, a point of intense light winks into existence. Over there, another. And another: tiny motes of cold fire mapping a sparse star field over the ground. I walk up to one, kneel and peer carefully at the other-worldly brilliance. It comes from the tail end of a small, elongated, wingless beetle, clutching hold of a stem of grass and waving its abdomen in the air. It and the lights around me are glow-worms, Lampyris noctiluca, things both sublime and ridiculous: half intimations of remote stellar distance and half waggling beetle bums.
Only female glow-worms shine like this. They can’t eat, drink or fly but spend their days burrowed deep in stems and under debris, emerging after twilight, when the light drops to around 0.1 lux, to clamber up plant stems and glow to attract the smaller, winged males. Once mated, the females extinguish their light, lay between 50 and 150 small, spherical, faintly luminous eggs and die. Their adult lives are short and made of light – but in their two years as larvae, they are creatures of macabre darkness, using their jaws to inject snails with paralysing, dissolving neurotoxins before sucking them up like soup.
As I kneel by the glow-worm, transfixed by its light, this encounter in the summer night feels more like the workings of magic than chemistry, though I know that the light is the result of a reaction when the enzyme luciferase acts upon a compound called luciferin in the presence of oxygen, adenosine triphosphate and magnesium. The precise mechanism of their cold luminescence long puzzled natural philosophers. In the 17th century, Robert Boyle found that the glow was extinguished if they were kept in a vacuum – although, noticing that when kept in crystal glasses between experiments they continued to glow, he mused that their light was akin to “certain truths” that shine freely “in spight of prisons”. In the early 19th century John Murray conducted laborious experiments on Shropshire glow-worms, placing their luminous parts in water heated to various temperatures, or in acid, naphtha, oil or spirits. One specimen glowed for several nights when suspended in olive oil. “Viewed at a distance of about ten feet, it twinkled like a fixed star,” he recounted, while “the eye steadily and tranquilly observed the beautiful phenomenon”.
It is hard to write about glow-worms without recourse to metaphors of stars and lamps. Their beguiling effect on the observing eye and their singular light populate myriad works of literature; these are the creatures of an “ineffectual fire” in Hamlet and the “living lamps” in Marvell’s “The Mower to the Glow-worms”, courteous beasts that guide wanderers home to safety.
Glow-worms prefer chalky, limestone habitats and you can find them on old railway lines and embankments, in cemeteries, hedgerows and gardens. But no one knows how many there are in Britain. They often go unnoticed because their light is easily obscured by headlights and torches. Certainly they are threatened by habitat degradation and urban development – males are attracted to streetlights and brightly lit windows – and this colony survives partly because the sodium glow of the surrounding town is blocked by quarry walls. Because the females do not fly, colonies are often venerable in age and easily rendered extinct: it is hard for them to move. But where they are known, local colonies are often passionately guarded and night-time glow-worm tours have become a summer tradition in many parts of the country, local experts guiding visitors around the natural light show, often with drinks and snacks laid on.
We live in a world of distracting, glowing screens but even so, these shining, tiny beacons retain an allure that draws people out in droves to stand and wonder. It is hard in these days of ecological ruination to find ways to reconnect people to a natural world more commonly encountered on television and video than in living reality. The greatest magic of these creatures is that their light cannot be captured meaningfully on film. Glow-worms are part of our hidden countryside. Like Marvell’s living lamps, they are still able to guide us distracted wanderers, giving us a keen sense of place and showing us a way to think of the nature around us as home.
Helen Macdonald is the author of “H Is for Hawk” (Vintage)