When talking about light pollution, the first thing that often comes to mind is that in cities, stars are no longer visible at night. While this is a loss of the natural beauty we all experience, artificial lighting has much more severe consequences for insects. In fact, it likely significantly contributes to their drastic declines, as 40% of all insect species are under threat.
Please also read: Engaging locals with Insect Respect
Light affects insects in many different ways. To give some examples, light attracts many insect species, but this attraction is fatal – one third of moths that gather around a light bulb die before morning. They either die from exhaution or predators eat them, as light makes it easier for them to find prey. Other insects deliberately avoid light, which means that decline in dark places shrinks their habitat.
Light as an important cue
Many insect species depend on light cues for their development, mating or activity patterns. The patterns of day and night have been the same through 4.6 million years of Earth’s existence. This makes it extremely hard for wildlife to adapt, as this change is unprecedented. There has been climate change, naturally invading species or habitat degradation before, but day and night patterns have never changed. Light has always been a very reliable cue about the environment, but that’s something that is changing now.
Along these lines, dung beetles use stars for navigation – but with light pollution, they cannot see stars anymore. Many insects only start to forage when it’s sufficiently dark. However, with artificial lighting, this period might be much shorter, leading to their starvation. In addition, firefly beetles use bioluminescence signals for mating, which are much less visible in light. In this way, their mating success drops drastically. Furthermore, light can directly sterilise males of some insect species, or change the sex ratio of parasitoid wasps, gravely affecting entire populations.
Light pollution and reproduction
Light can negatively influence the reproduction of aquatic insects in another way. Aquatic insects, such as mayflies, determine where to lay eggs by searching for polarized light. Such light occurs in natural environments where water bodies reflect moonlight, enabling insects to find water. However, with artificial lighting, polarized light is also on non-aquatic surfaces, such as asphalt. This reproductive failure can effectively decimate future generations.
Light also plays an important role in guiding the development of insects. The exact timing in the year when certain developmental processes in insects occur is often linked to the specific day length. As artificial lighting changes the duration of the darkness, it has the potential to affect the insect perception of day lenght, changing the timing of development.
What can we do?
Despite the significant negative effects light pollution has on insects, it is one of the easiest threats to prevent. By shielding, dimming and simply using less unnecessary illumination, the threat easily disappears. Therefore, make sure your backyard isn’t completely lit up, and try to shield both the downwelling and upwelling light coming from light sources.
Light pollution in Wilderness
In European Wilderness Quality Standard and Audit System, one of the criteria of Wilderness is also minimal light pollution. Wilderness should not have any light pollution, as not only is this important for all the wildlife living there, but also for Wilderness experience. As a pristine area with no human impact, also artificial light should not be present there. So let us give a new meaning to Black Friday, and raise awareness on the impact that our light pollution has on the world around us.