Glow-worm

Lampyris noctiluca

Despite their name, the glow-worm is actually a beetle, not a worm! The males look like typical beetles with wings and hard wing cases known as elytra. They are light brown in colour, have large photosensitive eyes, and measure c.15mm in length. The females look very similar to the larvae (known as larviform females), have no wings, and measure c. 20mm in length. The larvae have prominent pale yellowy-orange triangular markings at the side of each segment which are not present on the females. The female has a completely black back with a thin paler line down its centre, whilst the larvae tend to be more greyish-brown.

The female sits in high up on a grass stem at night emitting a steady (not flashing) yellowish-green light from the end of her abdomen. The male, larvae and eggs can also emit light, although much more weakly than the female. The light is used to attract a flying male.

The larvae are most often seen living under rocks on chalk or limestone grasslands and feeding on slugs and snails. They use sickle-shaped jaws to inject a toxin which both paralyses and liquefies their prey. Gardens, hedgerows, railway embankments, woodland rides, heathland and cliffs are all possible habitats for glow-worms. The adults do not eat anything, and only live for 14-21 days, until the female has mated and laid eggs. The larvae live a little longer and are seen between April and October.

Where and when to see them

Adults are only around for a short period in June and July, and the larvae between April and October.
Look for them in open, grassy areas.
Move away from artificial light such as street lamps, car headlights, and houses to see the greenish light of a glow-worm more clearly.

View a glow-worm 10km distribution map of Wales.

Legal status

None

Similar Species

Lesser glow-worm (Phosphaenus hemipterus)

The species is rare and currently confined to southern England. Both sexes are flightless. Females measure around 10mm, and the males around 7mm. The glow is feeble and rarely lights up unless disturbed, so the female probably draws in males using pheromones. The larvae mainly consume earthworms, whereas the adults are unable to feed with only vestigial mouthparts.

Did you know?

The light of a glow-worm is bioluminescent, i.e the result of a chemical reaction: a molecule called luciferin is combined with oxygen to create oxyluciferin, a light-emitting compound.