Twinkle, Twinkle Little Bug

From paralysing snails to lighting lamps, David Profumo shines a light on the life of a glow-worm, which isn’t actually a worm at all

It isn’t a worm, it’s an insect—one famous for a chemical romance that brightens up our summer gloaming with a mysterious greenish glow, a beetle that was once the slang word for those of us humble scribes who toil by lamplight. A member of the small family that includes European fireflies (they aren’t flies, either, by the way), the glow-worm is widely distributed across Asia and up to the Arctic. Worldwide, it’s related to many bioluminescent bugs, which include Antipodean cave-dwelling fungus mites and even a subtropical marine species.

Populations of Lampyris noctiluca are hard to monitor, but, in Britain, appear patchy and are thought to be in decline. they favour a chalk or limestone habitat, with a penchant for churchyards, golf courses or abandoned railway cuttings, and are best sought out from mid June, when their goblin lights may be spotted on warm evenings. Folk wisdom reckoned the glow bard’s seasonal display heralded the start of the hay harvest and the naturalist Muffet (whose daughter sat down on that tuffet) specifies it was ‘a sign of the ripenesse of Barley, and the sowing of Millet’.

Its conspicuous adult stage is a mere final fraction of the glow-worm’s life cycle. Autumn eggs (the coatings of which themselves occasionally glow, too) hatch after 35 days and the resulting larva is a frankly unprepossessing creature resembling a woodlouse.