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Health

Dung beetles use the polarization of sunlight to navigate.

Seriously, Science?By Seriously ScienceDecember 8, 2014 5:00 PM

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As we've said before, dung beetles are really awesome. Not only do they love poop, but to make sure they get their fair share, they form and roll giant balls of the stuff away to their underground lairs, a job that makes them important ecosystem managers. And if you're one of the poor souls who has never seen a dung beetle in action, here's a YouTube video to prove it:

[embed]http://youtu.be/Jsfq_aAWRwk[/embed]

How do dung beetles know where to take their precious cargo, you ask? A study we covered a few years ago showed that nocturnal dung beetles can navigate using the stars, specifically the pattern of the Milky Way across the night sky. But what about diurnal dung beetles that are active during the day? Well, these scientists set out to answer that question, and they came up with a fascinating answer. If it's visible, dung beetles use the sun's location to orient (not very surprising). However, these amazing creatures can still navigate when the sun is hidden. To do this, they take advantage of the fact that light becomes polarized when filtered through our atmosphere, a feature of sunlight invisible to our senses. Sunlight coming from different parts of the sky is polarized differently, allowing dung beetles to navigate even when the sun is not visible. Neat!

Diurnal dung beetles use the intensity gradient and the polarization pattern of the sky for orientation. "To escape competition at the dung pile, a ball-rolling dung beetle forms a piece of dung into a ball and rolls it away. To ensure their efficient escape from the dung pile, beetles rely on a 'celestial compass' to move along a straight path. Here, we analyzed the reliability of different skylight cues for this compass and found that dung beetles rely not only on the sun but also on the skylight polarization pattern.Moreover, we show the first evidence of an insect using the celestial light-intensity gradient for orientation. Using a polarizer, we manipulated skylight so that the polarization pattern appeared to turn by 90 deg. The beetles then changed their bearing close to the expected 90 deg. This behavior was abolished if the sun was visible to the beetle, suggesting that polarized light is hierarchically subordinate to the sun. When the sky was depolarized and the sun was invisible, the beetles could still move along straight paths. Therefore, we analyzed the use of the celestial light-intensity gradient for orientation. Artificial rotation of the intensity pattern by 180 deg caused beetles to orient in the opposite direction. This light-intensity cue was also found to be subordinate to the sun and could play a role in disambiguating the polarization signal, especially at low sun elevations." Related content: Galloping dung beetles, Batman! Scientists discover the first insects that gallop. NCBI ROFL: Dung beetles use Uranus for orientation. NCBI ROFL: Yes, dung beetles do have favorite flavors of poop.

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