When a scouting ant discovers a food source, it leaves an odor trail on its return trip to the nest that other ants can subsequently follow. As more ants travel the path, the scent becomes stronger and easier to follow. Audrey Dussutour of the Center for Animal Cognition Research in Toulouse, France, and her colleagues set up an experiment to investigate how overcrowding would affect the creatures behavior. The team provided black garden ants with a sugary source of food that was separated from their nest by a diamond-shaped bridge. When the two paths were 10 millimeters wide, the ants favored one branch, indicating their preference for a well-trodden path. The scientists then narrowed the two trails to increase congestion. According to the report, when the paths were six millimeters wide or less, the ants began to utilize both sections of the bridge equally because collisions between ants leaving the nest and those returning with food forced some of the creatures to take the second pathway.
"We have demonstrated the surprising functionality of collisions among ants to keep up the desired flow level by generation of symmetrical traffic," the researchers note. By rerouting themselves, instead of just returning to the nest because their desired path became unavailable, the insects maintain the optimal rate of food return.