Honey bee orientation: a backup system for cloudy days.

On cloudy days, honey bees are known to navigate to familiar food sources and orient their dances accurately. This capacity could be based on a magnetic compass sense, an ability to perceive the sun or patterns of polarized light through the clouds, or on the bees' memory of the diurnal course of the sun with respect to local landmarks. Experiments pitting these alternatives against one another demonstrate that the navigational backup system of bees is based on memory.