The internal computer
In the featureless, sun-scorched salt pans of the Sahara, the desert ant Cataglyphis fortis forages for heat-stricken insects. Its nest is a tiny, inconspicuous hole in the ground, nearly impossible to find by sight. After wandering on a long, tortuous path, sometimes for hundreds of meters, the ant must find its way back before it succumbs to surface temperatures that can exceed 60°C (140°F). To do this, it computes a direct, straight-line path back to the nest entrance. This computation is achieved by path integration, a form of dead reckoning. For decades, researchers at the University of Zurich, led by neurobiologist Rüdiger Wehner, have conducted elegant experiments to understand how the ant's tiny brain—with fewer than one million neurons—accomplishes this. The ant's brain continuously combines two separate streams of information: direction and distance. The result is an updated "home vector" that tells the ant the precise direction and distance to its nest from any point in its journey.
A celestial compass and a step counter
The ant's directional information comes from a sophisticated celestial compass. Specialized photoreceptors in the dorsal rim of its compound eyes can detect the polarization pattern of sunlight in the sky. This pattern, invisible to humans, provides a reliable directional cue even when the sun itself is not visible. Research from the University of Zurich has shown that this polarization compass is the dominant directional tool for the ants, even more so than the sun's position.