Dung beetles ignore landmarks for straight-line orientation

Upon locating a suitable dung pile, ball-rolling
dung beetles shape a piece of dung into a ball and roll it
away in a straight line. This guarantees 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 polarised light formed around these light sources
to roll their balls of dung along straight paths. Here, we
investigate whether terrestrial landmarks have any influence
on straight-line orientation in dung beetles. We find
that the removal or re-arrangement of landmarks has no
effect on the beetle’s orientation precision. Celestial compass
cues dominate straight-line orientation in dung beetles
so strongly that, under heavily overcast conditions or when
prevented from seeing the sky, the beetles can no longer
orient along straight paths. To our knowledge, this is the
only animal with a visual compass system that ignores the
extra orientation precision that landmarks can offer.