Human activities like deforestation and fossil fuel use are major drivers of biodiversity loss. But what about seemingly innocuous activities like turning the lights on at night? While most people who live in cities or suburbs are used to the effects of artificial lights, many wild animals that live alongside us are not so good at coping with this widespread form of pollution.

Ecologists in Finland recently published a study on the effects of artificial lights on mate attraction in a bioluminescent beetle species called the common glow-worm of Europe (Lampyris noctiluca). Female glow-worms use their bioluminescent abdomen to attract male mates, but this reproductive strategy only works at night, when the glowing signal is readily apparent. Artificial lights are making the night-time landscape much less dark in many places, which could reduce the glow-worms’ ability to find mates.

To test the effects of artificial lights on mate attraction, the researchers made fake female glow-worms and set up traps to capture any males that came in contact with them. Very few males approached female glow-worms that were just one meter from away from an artificial light, while they easily found the females that were over two meters away. So, mate attraction in these insects is seriously disrupted by artificial lights, but females might be able to compensate if they move further away from the light.

Unfortunately, the researchers ran another experiment and found that in the presence of an artificial light, female glow-worms are likely to not signal at all, or even hide, rather than to move further away. This unhelpful behavior is quite understandable considering that for most of the evolutionary history of these insects, artificial lighting did not exist.

The results of these experiments clearly demonstrate how detrimental night-time lighting can be for wild animals, especially nocturnal animals that use visual forms of communication such as bioluminescence.  And beyond these worms, artificial lights have also contributed to global firefly declines as well as the declines of many non-bioluminescent insects, such as moths, crickets, and mayflies.