Figure 1: An African dung beetle rolls its way through the starry night.
Source Credit: New York Times (LINK)
Those who have been to large, bright cities may have noticed something about the night sky: they are starless. And while this can be–and often is– quickly dismissed as a meaningless observation, it holds a lot of significance to other forms of life.
The night sky is more than just a pretty sight for animals like the African dung beetle. A discovery was made just over a decade ago that these nocturnal insects rely on the Milky Way to navigate through their dark environment in near-perfect straight lines. When the sky, however, is polluted with light sources from human civilization, these animals begin to lose their way.
New research published in the journal Current Biology at the end of July found evidence that man-made light disrupts the behavior of African dung beetles in South Africa. The unique ability of dung beetles to travel through the desert in almost perfectly straight lines is made possible by their compound eyes that are sensitive to dim objects. For some context, dung beetles have been observed to head in a random direction in a straight path as this limits possible encounters with other dung beetles (which frequently leads to fights). As they crawl along their paths, they look up at the sky to confirm that its view of the arrangement of stars matches preceding reference images.
As scientists were observing this behavior, they noticed that the Milky Way became increasingly more difficult to locate. Subsequently, they hypothesized that this loss of sight may impact the beetles in some way. To test their ideas, they conducted experiments where they shined spotlights on the beetles and studied their movements on the roof of a building in central Johannesburg.
The new research presents that when the sky was dominated by a single, powerful light, it could be observed that the dung beetles headed in a straight path for the light source instead of heading towards a random direction as they normally would. Even more concerning was when the light was scattered, creating a featureless night sky that resembles those in suburban areas. The beetles were completely confused and went around in circles.
Therefore, this new, threatening issue serves as a new challenge for dung beetles as it disrupts their everyday behavior. Scientists are concerned that other animals like birds and migratory moths may face heavy consequences from light pollution on a much grander scale. As the night skies continue to become brighter every year, it will become an important role for people to ensure that Mother Nature doesn’t step off her path.
Q&A:
Hannah: In addition to the city lights, does air pollution play any role in disrupting the behavior of the animals that rely on the stars?
While I wasn’t able to find much information on this topic, I did stumble across an article describing how light pollution can affect air pollution. City lights were found to slow a cleansing process that breaks down chemicals in the air. It was definitely an interesting read and I suggest you go read that as well.
Sally: Where are the dung beetles exactly heading towards?
As you may know, dung beetles survive by rolling up other animals’ feces. That is an essential element to their survival as it is a big part of their diet. In order to prevent competition for the ball of dung, within the species, they steer clear of other dung beetles.
Anna: How might we help these dung beetles and other animals from light pollution?
There are a lot of small ways for individuals to pitch in and diminish the effects of light pollution. For example, try to only install and use outdoor lighting when it is absolutely necessary. Another way could be to only use warm-colored LEDs.
John: Why are the beetles’ compound eyes sensitive to dim objects?
Dung beetles are able to see much better than humans in dark environments because their eyes contain multiple lenses that form a single image for its photoreceptor cells. The beetles have also evolved to process visual information differently than human beings, allowing them to detect light better at night.
Jennah: Are dung beetles the only specimen that are affected by man-made interference with the night sky? Could you provide examples of other organisms that could potentially be impacted by the pollution?
Great question. Light pollution is such a big problem because it affects life wherever civilization is. The tiny sand hopper, for example, relies on the moon to guide its foraging trips at night. An experiment showed that when they were exposed to artificial lights, their movement was much more random, they missed out on feeding opportunities, and migrated less often. This is concerning because of their important role as decomposers, this could lead to heavier consequences for the entire ecosystem as a whole.
Wooseok: What exactly are the implications of the dung beetles losing their sense of direction? Is a specific stage of their lives critically affected by this loss of orientation?
An inability to quickly separate itself from a pile of dung will theoretically lead to more encounters with other beetles, which may result in fights over the limited, shared resource.
Works Cited
Foster, James J., et al. “Light Pollution Forces a Change in Dung Beetle Orientation Behavior.” Current Biology, 29 July 2021, doi:10.1016/j.cub.2021.06.038.
Sokol, Joshua. “What Animals See in the Stars, and What They Stand to Lose.” The New York Times, The New York Times, 29 July 2021, www.nytimes.com/2021/07/29/science/animals-starlight-navigation-dacke.html.
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