The glow worm

David Chapman / 29 June 2021

Glow worms really are intriguing creatures and it is well worth having a look in your garden at night to see if you have any as garden guests.



The natural world is full of creatures with amazing adaptations showing the wonders of evolution, all we need to do is look and see. By day we might easily overlook a glow-worm but to see one at night is to witness a breath-taking treat.

The glow-worm, Lampyris noctiluca, is slightly confusingly named as it isn’t a worm at all, it is a type of beetle. It has a long, segmented body but its six legs are situated near the head making it an ungainly creature forced to drag itself around using its legs with the occasional push from its tail end.

Lifecycle of the glow-worm

A glow-worm takes two years to grow to its full size of about 25mm long. During that time it feeds on snails - small varieties of snail are preferred - and it undergoes a number of skin moults in order to grow. Once it reaches its final stage of growth, the adult glow-worm can no longer feed and it has just two or three weeks to mate and, in the case of the females, lay eggs.

Male glow-worms develop wings in their adult stage so they have the ability to fly but they can’t glow. It is the female glow-worm which gives the species its name. Being flightless and nocturnal she has evolved a perfect way of attracting the attention of the flying males, she glows.

The female stops glowing as soon as she has mated and her next task is to lay eggs. Within a few days she will die but a few weeks later her eggs will hatch to begin the life-cycle again. Interestingly it takes two years for a young glow-worm to reach adulthood so it isn’t unusual to find a colony of glow-worms which is strong in alternate years.

The glow-worm's diet

The diet of a glow-worm larva consists entirely of snails, so they are useful insects to have in the garden. Once the larva reaches maturity it stops eating.

How glow-worms glow

The astonishing ability to emit a bright green light comes about through a chemical reaction inside her abdomen, a process known as bioluminescence. The light is generated when a chemical compound known as luciferin combines with oxygen. To act as a catalyst in this reaction the glow-worm uses an enzyme known as luciferase but this isn’t an instant reaction so turning the light on or off takes at least a few seconds.

The light is emitted from underneath the final segments of the glow-worm’s abdomen. To make the most of her light she might climb in the vegetation and arch her body to turn her underside to face upwards. By moving her body she lures males to her light and the larger the light source the more successful she is likely to be, so bigger, brighter females are more likely to mate and pass on their genes to the next generation.

When to spot glow-worms

Their peak glowing period is June to early August, they like dry, calm evenings and begin glowing as it goes dark, so about 10pm onwards. If you take a torch to look for glow-worms avoid shining it directly at them because they will slowly turn off their light and this might prevent her from finding a mate.

Dry and relatively warm springs provided ideal conditions for glow worms so there are many more sightings than usual when the conditions are right.

Where to see glow-worms

Glow-worms can be found all over the UK. They live in a variety of habitats including dunes; roadside verges; gardens; hedgerows; railway embankments; woodland rides and heathland. It is thought that they might have a preference for limestone or chalky soils, though they can be found on a wide range of soil types. Their distribution is tied in with their specific needs such as an abundance of the appropriate types of snail for them to eat and the mixed areas of grassland and bare ground which they seem to like.

Glow-worms can be found all over the UK but they are quite localised. Good details about their distribution in all counties can be found on the website: www.glowworms.org.uk

Glow worms in the garden

If you have glow-worms in your garden then it would be great if you could manage part of it as a habitat for them. They are a declining species and need our help. If you do have them the chances are you won’t have to do too much because you must already be doing the right things.

Glow-worms like a mixed patch of longer grasses combined with some bare patches of ground and shorter grasses. These longer grassy areas should ideally connect to larger areas of natural habitat such as a hedgerow leading out into the countryside if that is feasible. Insects need warmth so a sunny, south-facing spot would be good and maybe a pile of logs or rocks in the longer grasses might provide them with somewhere to bask.

It is best to leave the cutting of longer grasses until late summer or autumn when the glow-worms have finished their mating period and then I would recommend cutting area of grass at different times (see next month’s article on meadows). Clearly it is best to avoid using slug pellets, pesticides and weedkillers.

If you don’t have them in your garden you might be interested in looking for them nearby. Rather than heading off randomly at night to look for them I would recommend looking at the nature walks led by your local Wildlife Trust, they might have something on offer, or visit the website www.glowworms.org.uk. Here there is detail, county by county, of places where they have been spotted in the past as well as a wealth of other information about glow-worms.

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