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How Do Ants Make Sense of Gravity? A Boltzmann Walker Analysis of Lasius niger Trajectories on Various Inclines

Figure 1

Effect of the support inclination on A — typical trajectories of ants, B — statistics of headings and C — statistics of positions.

Slopes are indicated by labels , and illustrated by the (arbitrarily) increased length of the vectors on the left, heading uphill. Trajectories are 8.95, 2.28, 1.86, 2.30 and 0.67 meters long respectively. The statistics of headings, shown in B, compiles all ants' headings over time estimated every second. They show that ants are more and more often aligned with the steepest line as the inclination becomes steeper. Over time, this consistently biases the positions of ants towards locations uphill or downhill (up or down on the graphs A). This bias is summarized in C, using as proxies the absolute values of horizontal versus vertical coordinates of ant locations averaged over time for each ant (one dot per ant) for each inclination (red dot: and locations averaged over time and ants, red line: ). The higher values in indicate that the ants are on average further away from the center along the steepest line ( axis) than along the horizontal line ( axis), meaning that ants are more dispersed in the direction. Both types of distributions are significantly different from homogeneity even for the smallest incline .

Figure 1