Street lights making it harder for glow-worms to mate – experts

The glare of white artificial lights is preventing male beetles from finding females, scientists say.

Street lights are making it harder for male glow-worms to find and mate with females, according to scientists.

Research by UK zoologists has shown that the glare of white artificial lights is dimming the glow of potential mates.

The researchers said their findings, published in the Journal Of Experimental Biology, highlight potentially devastating consequences for glow-worm populations in the UK and around the world.

Jeremy Niven, professor of zoology at the University of Sussex’s School of Life Sciences, said: “Recent studies have documented large-scale declines in insects, which has serious consequences for agriculture and the ecosystems that depend upon insects.

“Light pollution has emerged as a key threat to insect populations alongside climate heating and land-use change.”

Some studies have claimed that glow-worms are disappearing from our landscape

Prof Jeremy Niven

Glow-worms are small, narrow beetles that can be found living under rocks on chalk or limestone grassland.

Habitats include gardens, hedgerows, railway embankments, woodland rides, heathland and cliffs.

The males look like typical beetles but the females look similar to the larvae and emit a bright green light at night.

They climb up plant stems and glow in order to attract males, who have large eyes sensitive to this type of light.

Many experts believe that the species is declining.

Prof Niven said: “Glow-worms could be considered a ‘canary in the coal mine’ because they are nocturnal insects that depend on a bioluminescent signal – females use a bright green glow to attract males for mating.

“Some studies have claimed that glow-worms are disappearing from our landscape.”

For the study, the researchers placed male glow-worms in a Y-shaped maze in their laboratory free from artificial light.

The team made a fake female and used a green LED light to illuminate it and recorded how long the male took to find it.

The researchers then gradually made the maze brighter by inserting LEDs to mimic street lights.

Brightness of this light ranged from 25 Lux – about 25 times brighter than moonlight – to 145 Lux, equivalent to the light beneath a street lamp.

Results showed all of the glow-worms found the LED in the dark.

However, when white light was at its dimmest, only 70% found the glowing fake female, while just 21% of the glow-worms studied found the dummy mate in the brightest light.

Prof Niven said: “We found out that the white light slowed the males’ approach and prevented many of them reaching the female.”

And for those who managed to reach the dummy mate, the journey was at least 12 seconds longer or more.

The researchers believe male glow-worms were unable move towards the females because they were dazzled by the white light.

Prof Niven said: “When males are exposed to bright white light they pulled their head back behind a sort of shield they have on their head and stop moving.

“We don’t know exactly what the shield does but we think it acts like sunglasses to reduce the glare of bright light.”

The researchers believe their work could help in better understanding how to protect glow-worm populations in meadows and heaths without the need to go completely dark.