FIGURE 3. Experimental results.

a, Experimental frequency distributions of the proportion F_1j of ants using the right branch for different branch widths. We considered traffic to be asymmetrical when more than 2/3 of the cumulated traffic of ants at the end of the experiment had used a single branch. All experiments have been pooled. b, Experimental frequency distributions similar to a, but for different total numbers of ants crossing the bridge. All experiments on bridges of w = 1.5, 3.0 and 6.0 mm have been pooled. c, Proportion of outbound ants on the left and right branches of the bridge divided by the total number of ants that have passed the bridge at the end of the experiment. The results contradict opposite one-way flows on both branches. d, Number of pushing events as a function of the total number of ant encounters on the initial part of each branch of the bridge. For each branch width, pushing events were evaluated at both choice points, for outbound and nestbound ants, during the first ten and last ten minutes of a random sample of two experiments characterized by symmetrical and two experiments characterized by asymmetrical traffic. This yielded a total of 2 branches 4 experiments 2 time intervals = 16 points per branch width. When the number of encounters was too low (3) the points were not taken into account in the regression. The slope of the linear regression is equal to 0.571 0.057 (confidence interval, CI_95%). This corresponds to the probability that an ant will be pushed and redirected towards the other branch after encountering another ant coming from the opposite direction (see e–g).