White LED light intensity, but not colour temperature, interferes with mate‐finding by glow‐worm (Lampyris noctiluca L.) males

Abstract

Artificial light at night is an increasing threat to nocturnal biodiversity. Aside from the overall increase in light emission, replacement of old monochromatic streetlighting by broad emission spectrum LED lights may be an additional threat. Studies evaluating the impacts of these artificial lights on the nocturnal European common glow-worm (Lampyris noctiluca L.) are scarce. This study examines the effects of upward facing white LED lights on the mate seeking activity of male glow-worms. Therefore we used traps with dummy females along a distance gradient from LED lights with different intensities and colour temperature (cold and warm white) and counted the number of males attracted per trap. We found that upward facing white LED light negatively impacted the males’ ability to locate the females, at previously unreported low light levels, while colour temperature did not affect the outcomes. More research on the effects of light pollution and their underlying mechanisms is needed to evaluate the impacts of this emerging and widespread threat on mating success and population persistence of glow-worms. Our study has important implications for glow-worm conservation as we showed that white LED lights, which are increasingly used on a large scale as streetlighting and other outdoor lighting, have strong negative impacts on the mate finding success of glow-worms, even at low light levels. We have furthermore demonstrated that colour temperature does not mitigate the lowered mate attraction success of dummy females under white light.