Certain dung beetles roll their dung balls in a straight line away from competitors at the pile by orienting to which celestial cue, even on moonless nights?
- The band of light from the Milky Way
- The pole star's fixed position
- The moon's changing phase
- Polarized light scattered by passing clouds
Why A? And why not the others?
Correct answer: A. The band of light from the Milky Way
Research by Marie Dacke and colleagues showed that African dung beetles can use the Milky Way's faint band of light as a compass to roll their dung ball in a straight line away from the competitive scrum at the dung pile, making them the first animal confirmed to navigate by the galaxy itself; in planetarium tests, beetles under a full starry sky rolled just as straight as beetles shown only a simulated Milky Way band, while beetles under a blank sky wandered randomly. Many other animals do rely on the fixed position of a pole star or on tracking rotating star patterns for orientation, but this study isolated the Milky Way's diffuse glow specifically as the beetles' cue. Moon phase and moonlight polarization do help dung beetles orient on nights when the moon is up, but the beetles in this landmark experiment still rolled straight with no moon present at all, showing the starlight-only channel works on its own. Clouds scattering polarized light is not a documented dung beetle navigation cue.
Source: Dacke et al., 'Dung Beetles Use the Milky Way for Orientation,' Current Biology 23(4), 2013; Lund University.