Scientists warn light pollution endangers glow-worm populations

By Chris Dyer via SWNS

Dazzling lights risk endangering glow-worms because light pollution blinds them from being able to find mates, scientists warn.

Increasingly bright cities could block male glow-worms spotting females - greatly reducing their numbers, researchers discovered.

The insects even cover their eyes with a head shield due to the bright lights - acting like a pair of sunglasses and cutting the amount of light they see, experts said.

While artificial light has helped increase human productivity, some nocturnal animals have been badly affected by the illuminations.

From increasing the amount of time predators are active to disrupting migrations, light pollution affects many animals in many different ways.

Female common glow-worms - known as Lampyris noctiluca - emit a green glow from their abdomen to attract flying males, but they are unable to fly themselves to new areas to escape light pollution.

Scientists examined how hard it is for male common glow-worms to find mates in an ever-brighter environment.

They discovered white light makes it harder for male glow-worms to find glowing females with potentially disastrous consequences for global glow-worm populations.

Professor Jeremy Niven, an expert in zoology at University of Sussex that carried out the study, said: "Keeping their eyes beneath their head shield shows male glow-worms trying to avoid exposure to the white light, which suggests that they strongly dislike it."

After collecting glowworms at night from the South Downs in East Sussex, researchers transported them back to the lab, before transferring the male insects to a Y-shaped ‘maze’ without exposing them to artificial light.

The team put male glow-worms at the bottom of the Y and a green LED, which mimicked a female’s glow, at the top of one of the arms, which the male had to walk toward.

They then recorded if and how long it took the males to find the fake female.

Researchers switched on a white light above the maze, ranging from 25 Lux - 25 times brighter than moonlight - to 145 Lux, which is the equivalent to the light beneath a streetlamp.

While all of the glow-worms found the LED in the dark, only 70 percent found the LED at the dimmest levels of white light, and just 21 percent of the insects found their potential mate in the brightest light, the researchers said.

Not only did the white light affect the glow-worm’s ability to find a female, but it also caused them to take longer to reach the LED, scientists said.

In the dark, the worms took roughly 48 seconds to reach the female-mimicking LED, but it took the same glow-worms around 60 seconds to reach the LED in the lowest white light levels, the study found.

Illuminating the maze also caused the male glow-worms to spend more time in the bottom part of the maze without moving toward a female, according to researchers.

In the dark, the insects only spent about 32 seconds in the bottom of the Y, while they spent around 81 seconds in the bottom of the maze in the brightest conditions, it was said.

Estelle Moubarak, a research fellow at the University of Sussex, suggested male glow-worms were unable to move toward the females when dazzled by white light.

This was because they cover their compound eyes - common on many insects - with a head shield, which acts like a pair of sunglasses, reducing the amount of bright light they see.

In fact, when the white light illuminated the area with the fake female LED, the glow-worms shaded their eyes for roughly 25 percent of the trial compared to only around 0.5 percent of the time when the maze was in the dark, the researchers said.

The study authors added: "So, while our bright night-time world has helped give rise to our modern society, it has had a drastic impact on male glow-worms and their ability to find mates.

"If this trend holds true, meadows and heaths across Europe and Asia that have lit up with the twinkling of the female glow-worms for millions of years will fall dark."

These findings were published in the Journal of Experimental Biology.