Temporary light exposure affects mate-searching in male glow-worms

Artificial light at night (ALAN) has been shown to negatively impact many species, particularly nocturnal ones, yet the underlying mechanisms driving these effects remain poorly understood. Various conservation measures have been proposed, including part-night lighting regimes and the dimming of artificial lights. In this study, we investigated how such temporary exposure to artificial illumination affects mate-finding success in the European common glow-worm, Lampyris noctiluca (Linnaeus, 1758), a nocturnal bioluminescent beetle. We examined the effects of different light intensities and exposure timings on male mate-searching behaviour, in a controlled indoor arena setup, where males could move freely toward a dummy female. Temporary exposure to strong white light (100 lx and 4315 lx) at the onset of the activity period caused a delay in the onset of mate searching. We suggest that this latency was induced by the time required for dark adaptation of the eyes following light exposure. In addition, under very bright light (4315 lx), males appeared to experience a reduction of activity, possibly as a lingering inhibitory effect of the light exposure. As a result, their overall mate-searching period was reduced: males were less active at the beginning of their activity window and ceased searching at the same time as control individuals that had not been exposed to artificial light. These findings suggest that part-night lighting regimes might not be fully effective as mitigation strategies, though they are preferable to no light reduction at all. Our findings also underscore the importance of considering both light intensity and timing when developing conservation strategies. Implications for insect conservation : Our findings indicate that even temporary exposure to artificial light can disrupt mate-finding behaviour in glow-worms. Effective mitigation strategies must consider both the intensity and timing of artificial light to reduce its ecological impact.