Transcript

Picture yourself in a savannah, in the early night.

[cricket sounds fade in]

You are standing next to a big pile of fresh dung.

[fly noise fade in]

You are a dung beetle, and you just finished assembling a big ball of dung. It is going to be all the food your offspring needs to grow into a beautiful beetle like you! But right now, what you need is to get away from the mound of smelly gold next to you. It attracts a lot of competitors, who might try to steal your hard work. Especially the new comers, still warm from their flight, faster than you. The best thing to do is to get some distance between you and this dung beacon as fast as possible! Then when you are far away, you can start digging a chamber to bury your treasure.

You don’t have anywhere specific to go, just away from the dung. The faster is simply to roll you ball in a straight line, keeping the track. But how to know which way is straight? This is not easy, for your small beetle brain. You don’t have a compass. There are no landmarks to use around. But you have a neat trick, a small area on top of your eye. The light receptors there are able to perceive the polarization pattern of the young night’s sky. For you, the skylight after sunset is like a giant compass, with all its light polarized in one direction. Using this simple cue, you can keep straight even after obstacles, or entomologists disturbing you.

This way, you can be sure that you reach a safe place to make your burrow.

Sources

Dacke, M. et al. (2013) ‘Dung Beetles Use the Milky Way for Orientation’, Current Biology, 23(4), pp. 298–300. Available at: https://doi.org/10.1016/j.cub.2012.12.034.

Dacke, M. (2014) ‘Polarized Light Orientation in Ball-Rolling Dung Beetles’, in G. Horváth (ed.) Polarized Light and Polarization Vision in Animal Sciences. Berlin, Heidelberg: Springer (Springer Series in Vision Research), pp. 27–39. Available at: https://doi.org/10.1007/978-3-642-54718-8_2.