Once a beetle (Scarabaeus satyrus) has constructed its dung ball, it moves off in a straight line in order to escape from rival beetles as quickly as possible, lest they try and steal its carefully crafted ball. This behaviour doesn't sound complicated, but several years ago, Marie Dacke of Lund University in Sweden and colleagues showed that polarised light from the moon is important for dung beetles to keep to a straight line.

Then the researchers were surprised to find the insects were able to stay on course even on a moonless night. "We thought there was something wrong in our set-up," Dacke says.