Dung Beetles: Guided by the Stars
Many animals are known to orient themselves according to the Sun, and some even to the Moon, but the dung, or scarab, beetle, has become the first known insect to use the stars. Once the beetles find a good dung heap they roll their ball away in a straight line to avoid coming full circle back to the original source. This means that heading off in the right direction initially is very important. If they get it wrong, they could bump into another beetle that might steal their dung.
Scientists led by Dr Marie Dacke from Lund University, Sweden, were puzzled at how the dung beetles still managed to navigate away from potential thieves on clear nights with no moon. Trying to work out what other indicators the beetles might be using, they carried out experiments in the field by attaching pieces of cardboard to the beetles to impede their vision. When placed in an arena with a dung ball in the middle, the shielded beetles took far longer to reach the edge than the control beetles, which had clear caps.
In the first experiment, the beetles might have been able to use other landmarks, like trees, as visual cues so a second experiment was designed so that the beetles could only see the sky. The time taken for the beetles to reach the edge of the arena on moonless nights was not significantly longer than on nights with a full moon. Beetles with cardboard caps, however, took much longer to navigate, as did all beetles on an overcast night.
A further experiment was designed to work out how exactly the beetles used the stars by changing projected lights in a planetarium. Here they found that the beetles could navigate just as well using only the (artificial) Milky Way as when 4000 stars were projected. These beetles are not only the first insects to use the stars to navigate, they are the first ever animals to have been shown to specifically use the Milky Way.
Following the publication of their paper in the journal Current Biology, Dr Dacke says that the team will “continue to look at how the starry sky looks through the eyes of the [dung] beetles… since there are still many things about celestial orientation in beetles that we do not understand.”
Dacke et al., Dung Beetles Use the Milky Way for Orientation, Current Biology (2013), http://dx.doi.org/10.1016/j.cub.2012.12.034