Wednesday, May 22, 2013

Dung Beetle Navigation

Dung beetles- Wikimedia
Many mammals and even the lowly box turtle can navigate by memory of the territory.  Some birds can even navigate by the stars. But dung beetles using the Milky Way?  Now that is an amazing story, as told in the New Yorker.

It begins with a dung beetle which shape its new found treasures into a ball and then laboriously rolls it away to an ideal place of burial.  There the female deposits a single egg in the dung which will serve as nourishment as well as home until the larva reaches adulthood.  I can only imagine its relief as it steps into the fresh air, but likely the beetle doesn't mind either way.

It has long been noted that dung beetles steer a perfectly straight course, a matter of efficiency as well as reducing the time they are exposed to competition for their prize or danger from a predator.  Just why any thing would want to eat a beetle rolling a ball of dung is a matter of conjecture.  Here we will concentrate on its navigation ability.

In the daytime, the beetles use the sun for their straight line navigation.  Sunlight is polarized and the beetles have special receptors that read the polarization.*  In 2003, Eric Warrant, a biologist at Lund and his colleagues determined that nocturnal dung beetles could navigate by the polarized light of the moon.  They also noticed that the beetles traveled relatively straight on moonless nights as well.  Since the beetle's compound eye could not detect a single star, the answer must have been the Milky Way.

A team led by Marcus Byrne, a zoologist at University of Witwatersrand studied the beetles on a box-like table which obstructed the view of trees etc.  Then they ran them with either clear or tiny black hats which blocked the view of the sky (I am not making this up) and showed that they navigated only when the sky was visible.  Finally they took them to a planetarium.  The beetles were lost when exposed to only the 18 brightest stars but were back on track when using the artificial Milky Way!  More detail in the New Yorker article.

Research like this might sound like a worthless study worthy of the Golden Fleece awards given to science that initially seems without merit.  Once again, there can be a practical application to pure research.  In this case, it comes from learning more about beetle vision.  Researchers are developing a few devices modeled on the talents of lowly insects. 

Nature.com shows how the compound eye of beetles have inspired a new type of camera, miniaturization including a large assembly of independent lens that keep objects in focus as they move away.  Another group shown at this site has developed a tiny flybot, a flying robot with flapping wings like its fly namesake.  You can watch it fly at this at NPR.org.

Flybots- NPR, Kevin Ma, Pakpong Chirarattananon/AAAS/Science

* Incidentally, polarized light is used on digital camera LCD screens.  If you are wearing polarized sunglasses and turn your camera 90 degrees, the screen appears black.  You aren't going blind, just a victim of modern technology.  Digicamhelp.com.
 

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