You might expect dung beetles to keep
their “noses to the ground,” but they are actually incredibly attuned to
the sky. A report published online on Jan. 24 in Current Biology,
a Cell Press publication, shows that even on the darkest of nights,
African ball-rolling insects are guided by the soft glow of the Milky
Way.
While birds and humans are known to
navigate by the stars, the discovery is the first convincing evidence
for such abilities in insects, the researchers say. It is also the first
known example of any animal getting around by the Milky Way as opposed
to the stars.
"Even on clear, moonless nights, many
dung beetles still manage to orientate along straight paths," said Marie
Dacke of Lund University in Sweden. "This led us to suspect that the
beetles exploit the starry sky for orientation—a feat that had, to our
knowledge, never before been demonstrated in an insect."
Dacke and her colleagues found that dung
beetles do transport their dung balls along straight paths under a
starlit sky but lose the ability under overcast conditions. In a
planetarium, the beetles stayed on track equally well under a full
starlit sky and one showing only the diffuse streak of the Milky Way.
That makes sense, the researchers
explain, because the night sky is sprinkled with stars, but the vast
majority of those stars should be too dim for the beetles' tiny compound
eyes to see.
The findings raise the possibility that
other nocturnal insects might also use stars to guide them at night. On
the other hand, dung beetles are pretty special. Upon locating a
suitable dung pile, the beetles shape a piece of dung into a ball and
roll it away in a straight line. That behavior guarantees them that they
will not return to the dung pile, where they risk having their ball
stolen by other beetles.
"Dung beetles are known to use celestial
compass cues such as the sun, the moon, and the pattern of polarized
light formed around these light sources to roll their balls of dung
along straight paths," Dacke said. "Celestial compass cues dominate
straight-line orientation in dung beetles so strongly that, to our
knowledge, this is the only animal with a visual compass system that
ignores the extra orientation precision that landmarks can offer."
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