Human light pollution risks extinguishing glow-worms: Study

The study was published in Journal, 'Journal of Experimental Biology.'

The bright lights of big cities are modern marvels, designed to help us work, stay safe, and enjoy the world around us long after the sun has gone down. While artificial light has increased human productivity, some nocturnal animals and even humans have paid a price for this illumination. Light pollution affects many animals, from increasing predator activity to disrupting migrations; but how do animals that use their own luminescence to lure food or attract mates fare against this new, brighter background? Female common glow-worms (Lampyris noctiluca) emit a green glow from their abdomen in order to attract flying males, but they are unable to fly away from light pollution.

As a result, Estelle Moubarak, Sofia Fernandes, Alan Stewart, and Jeremy Niven of the University of Sussex in the United Kingdom wondered how difficult it is for male common glowworms to find mates in an increasingly bright environment.

Moubarak collected glow-worms from the UK's South Downs at night before transporting them to the lab and beginning the difficult task of transferring the male insects to a Y-shaped'maze' without exposing them to artificial light. The male glow-worms were placed at the bottom of the Y, and a green LED, which mimicked a female's glow, was placed at the top of one of the arms, which the male had to walk towards. They then timed how long it took the males to find the phoney female. The team then turned on a white light above the maze that ranged from 25 Lux (25 times brighter than moonlight) to 145 Lux (equivalent to streetlight light).

While all of the glow-worms found the LED in the dark, only 70% found it in the dimmest levels of white light, and only 21% found it in the brightest light.

The white light not only hampered the glow-worm's ability to find a female, but it also made them take longer to reach the LED. The worms took 48 seconds to get the female-mimicking LED in the dark, but 60 seconds to reach the LED in the lowest white light levels. The male glow-worms spent more time in the bottom part of the maze without moving towards a female after the maze was illuminated. In the dark, the insects only spent ~32s in the bottom of the Y, while they spent ~81s in the bottom of the maze in the brightest conditions.

Moubarak suggests that male glow-worms were unable to move towards the females when dazzled by white light because they cover their compound eyes 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 ~25% of the trial compared to only ~0.5% of the time when the maze was in the dark.

'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,' says Niven. So, while our bright night-time world has helped give rise to our modern society, it has had a drastic impact on male glowworms 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. (ANI)