Writing about the glow-worm, Lampyris noctiluca, in his ‘Book of Insects’, the 19th Century French naturalist Fabre suggested that few insects enjoy more fame than the Glow-worm who celebrates the joy of life by lighting a lantern at its tail end. But it is only the female glow-worm which lights ‘a lantern’ - and this is to attract a mate!
The adults exhibit sexual dimorphism with both sexes being distinctly different in both appearance and behaviour. The adult female looks very similar to the larval form but produces a bioluminescent glow by a chemical process that occurs in specialised organs present in the abdomen; although this light may steadily shine for several hours each night until a partner is found, its attraction is enhanced by the rhythmic waving of the abdomen. The male glow-worm is actually smaller than the female and has the appearance of a more typical beetle by having a pair of wings protected by an outer pair of hardened forewings. It flies a metre or so above the ground seeking the females which signal from grass stems and other high parts of the vegetation.
After mating, the female completes her short adult life by producing up to 100 eggs before dying. The eggs hatch after a few weeks, and the emerging larvae spend the next few years (during which period they moult several times) foraging in leaf litter and feeding on slugs and snails which they inject with digestive enzymes before consuming the liquified contents. The larvae differ in appearance from adult females by having a bright spot on each side of its segments.
Glow-worms may be observed at night between May and September on meadows and grasslands.
