Beetle Lights

The Milky Way arcs high across the sky this evening. Unfortunately, the light of the full Moon makes it almost impossible to see. That’s both good news and bad news for the dung beetle. It navigates by the Milky Way, so that glowing band won’t do it any good. But it also relies on the quality of moonlight, so it should still be able to find its way around the dung piles — if it’s not near a city.

Many nighttime animals navigate with the help of the sky — birds, butterflies, sea turtles, and many others. Most appear to be guided by the stars, although some also rely on the Moon.

But the dung beetle is the only one that’s known to navigate by the Milky Way. Lab studies have shown that it can sense subtle differences in light levels. Since the Milky Way is uneven, the beetle can follow the Milky Way’s bright and dark patches to roll its dung ball to a good hiding place.

Studies have also told us that the beetle can follow the moonlight. In particular, it follows polarized light — light waves that are all reflected in the same direction. The beetle is one of the few creatures that does so.

But a study in 2021 found the dung beetle is facing a challenge: light pollution. Researchers compared the behavior of dung beetles near a bright city with those under dark skies. The brighter skies block the Milky Way and interfere with the moonlight. So the city beetles start using city lights as beacons — replacing nature as their guiding lights.
 

Script by Damond Benningfield