Homeward-bound Ants Use Angular Signposts
Foraging ants use a beautifully simple system of signposts to get home, a study in the December 16, 2004 Nature shows. Their pheromone trails always fork at the same angle, meaning that an ant arriving at a junction can always tell which way is home and which way wilderness lies.
Trails laid down by Pharaoh’s ants (Monomorium pharaonis) always branch so that the two forks form an angle of 53 degrees, report Duncan E. Jackson and colleagues. This means that an ant reaching a junction when facing away from the nest will find both trails leading off at the same angle relative to their current heading. But an ant facing homeward will find one large angle and one acute, a difference that enables the ant to choose the correct path back to the nest.
Ants placed on artificial trails using different angles were more frequently confused, the researchers report. The discovery answers the question of how ants incorporate directional information into their pheromone trails without resorting to complex gradients of chemicals.
