There are two species of glow worms in the UK. The ‘common’ Glow worm (Lamphyris noctiluca) and the rare Lesser glow worm (Phosphaenus hemipterus), that is only know from a few sites in Hampshire and Sussex.
Glow worms are actually beetles rather than worms. From June to August, the wingless females climb-up grass stems at dusk and begin to glow with a pale-green light (bioluminescence) to attract the flying males. The males look much more like a ‘real’ beetle than the females- which don’t have wing cases. The males, larvae and even the eggs can ‘twinkle’ occasionally.
The glow worm spends most of its life as a juvenile. The larvae have pale spots along the sides of their segmented body, and can spend up to 3 years feeding on snails, before turning into an adult. The adults don’t eat and live for only a few weeks, searching for a mate and die shortly after laying their eggs.
The adults and larvae are generally nocturnal, but may be discovered resting under stones or logs during the day. Females tend to start glowing around 10pm until midnight (possibly slightly later in the far north of Scotland where the days are longer and nights shorter in mid-summer).