Glow Worms

Posted by Michael Williams - MCIEEM BSc (Hons) on 11/06/2014

As a teenager I used to hear older naturalists comment frequently that there used to be a lot more glow-worms back in their day. Nowadays I find myself saying the same thing.

Alongside the footpaths, back lanes and disused railway lines of north Devon I would often pass the green glow of the females in the grassland and low scrub.

There are two species of glow worm in Britain. The lesser glow worm is very rare and confined to a handful of sites in England and Wales, however it is a small species with a very feeble glow, and may therefore be overlooked. Glow worms are beetles (not worms!) and are related to the fireflies.  The female is flightless and the hard wing-cases are very small, and it doesn’t at first-glance appear to resemble a typical beetle. The male looks more like a typical beetle, with wing-cases covering the entire abdomen. Only the female emits the strong green glow, which they use to attract males. The male can emit a very faint glow, but this is not very obvious. Glow worms spend most of their life as a larvae, which resemble the adult female glow worms, and feed on other invertebrates such as snails. I have occasionally seen them walking along the edges of footpaths on early summer evenings. The adults cannot feed, and only live for around two weeks between June and August. The best time to look for them is on moonless nights.

According to the UK Glow Worm Survey, most glow worm colonies have probably been close to their present locations for a long time, possibly hundreds or thousands of years. Attempts to relocate them or introduce them to new areas are usually unsuccessful. One of the main reasons for their decline is thought to be artificial lighting, as the males are attracted to these and therefore in well-lit areas their chances of finding females to mate with are reduced. Change in land use are also probably a significant factor, however more work needs to be done to fully establish the threats to glow worms.

If you find a site with glow worms, the glow worm survey would appreciate your records. The recording form can be found at:

Ecosulis has considerable experience in undertaking invertebrate surveys across the UK and can offer practical advice on invertebrate conservation and mitigation for endangered species.

Image courtesey of Dave Evans: