Navigating While Walking Backward

Pavement Ants

The Spanish Desert Ant, Cataglyphis velox is a good model for studying orientation. They live in the desert where the landscape is flat and relatively uncluttered. Ant colonies have many individuals that can provide a pool of test subjects.

Ants that locate food will orient back to their nest using landmarks and the position of the sun. A group of scientists* placed an arena next to an ant nest and placed cookie crumbs in the arena some distance from the nests. After an ant picked up a cookie, they placed a barrier in the ant’s path so that it could not follow the straight path leading from the nest to the cookie crumb.  The ants were forced on a detour.  When the ants were forced to follow a path 90 degrees from the straight route to the nest, ants would carry the cookie crumbs to the edge of the barrier, make the appropriate turn and return to the nest. The scientists concluded that the ants could see as they walked and used landscape scale cues to navigate.

Navigation was successful if the ants carried small cookie crumbs and walked forward. Slightly larger crumbs cannot be carried forward by the ants. Instead, the ants must drag the larger crumbs while walking backward. When backward walking ants were blocked by the barrier, many of the ants failed to navigate the turn at the end of the barrier and headed off into the desert. Some backward walking ants did negotiate the turn by using a different behavior. These ants walked backward with the large crumbs for a short distance, dropped the crumb and looked around. They repeated this behavior when forced to detour.  These ants were able to recognize the nest location when they reached the end of the barrier because within a short distance, they would drop the cookie crumb and look around facing forward.  Apparently, ant navigation does not work as well in reverse.

Sebastian Schwarz, Michael Mangan, Jochen Zeil, Barbara Webb & Antoine Wystrach. How Ants Use Vision When Homing Backward. Current Biology. Volume 27, Issue 3, p401–407, 6 February 2017
DOI: http://dx.doi.org/10.1016/j.cub.2016.12.019