One of Britain’s most adored yet mysterious insects, Glow-worms face many modern-day threats and challenges affecting their future existence. Glow-worms, despite their name, are beetles belonging to the family Lampyridae, commonly known as fireflies. This beetle is characterised by its bioluminescent light used for attracting mates. There are over 2,200 lampyrid species globally yet only two are found in the UK. Lampyris noctiluca, also known as common Glow-worm, is the species most often seen in the UK, and are also found across Europe and Asia.
Glow-worms are widespread across the UK with localised populations in Scotland, favouring chalky or limestone areas with open grass or hedges. Despite its common occurrence, the Common Glow-worm faces threats from habitat loss, agricultural intensification and chemicals, and light pollution. Recent assessments of European Glow-worm species led by the IUCN Firefly Specialist Group, found the Common Glow-worm is experiencing declines in parts of its range, particularly in the UK. The 2024 assessment has classified L. noctiluca as Near Threatened according to the IUCN Red List criteria.
The male Glow-worm looks like an ordinary beetle with hard wing cases; however, the adult females are wingless, larger than the male and can produce a bright greenish-yellow glow from the underside of her body. This glow is caused by a chemical reaction within the beetle, and it is used to attract a mate. It’s not unusual to find several male Glow-worms trying to mate with the same female. The females glow for several hours at a time as soon as it gets dark but switch off their glow once they have mated. The larvae look very much like the wingless females and glow faintly. Glow-worms do all their eating during their larval stage, feeding on small snails. Adults are active between May and September. Larvae can be seen between April and October.
Image: © Pchelovek1205, (CC BY – SA 4.0)
Action Needed
Artificial lighting and protection of the nocturnal environment:
- Awareness raising on the importance of nocturnal environment. This can include lodging light pollution related Motions, asking Parliamentary Questions and leading debates in the Parliament.
- Support Buglife’s ‘Don’t Neglect the Night’
- Address light pollution in environmental policy and legislation, introducing a single driver for light pollution including setting binding environmental targets to reduce existing levels.
- Implement national monitoring of light pollution levels.
- Update planning guidance in line with advanced lighting technology to include proper consideration for the impact of light pollution on ecology, human health, and society.
- Support local authorities in managing light pollution through guidance, funding, and regulation.
Habitat connectivity:
- Safeguard open and unimproved grasslands.
- Embed habitat restoration in land-use planning.
Chemical free habitats:
- Glow-worm larvae depend on abundant invertebrates, especially snails and slugs, as their primary food source. Push for chemical-free habitats to allow these prey species as well as Glow-worms thrive.
Threats
Habitat loss and fragmentation: Loss and fragmentation of grasslands driven by agricultural intensification and woodland succession following the abandonment of pastureland are the primary contributing factors threatening common Glow-worm populations. Habitat fragmentation is particularly stressful for non-flying adult females who are confined to their hatching sites, leading to localised extinctions. Changes in land use such as road construction, ditch filling, and timber stockpiling, as well as drought, are also threatening Glow-worm populations.
Use of pesticides: Pesticides are harmful to a range of different life stages of the Glow-worm. Exposure to chemicals from agriculture and garden applications directly kill the insect larvae as well as prey species, contributing to reductions in larval survival. The chemicals in soil further contribute to habitat degradation.
Light pollution: Very low levels of light pollution interfere with males’ ability to locate glowing females, while females rely on sunset as a cue to glow, this can be obscured by light pollution hindering reproduction. Even temporary exposure to artificial light impairs male navigation, reducing search speed and orientation towards females. Light pollution has increased by at least 49% over 25 years and continues to be overlooked in efforts to restore national biodiversity.
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