physiology - Do Ants have a sense of Direction?

Do ants understand which way is up or down?

Could they differentiate between uphill and downhill?

Answer

Actually No.

Amazingly there is this paper published on the motions on Ants which says:

The isotropic distribution of average speed appears as a surprising result since it would be expected, for instance, that ants progressing uphill should be slower than when moving downhill. For instance, Seidl et al. found lower speeds on steeper inclines in desert ants moving uphill, but indicate that desert ants progressing downhill displayed high velocities [42]. This is in contrast with our finding with Lasius niger in the present set-up where the velocity showed no dependency to the walking direction, even for the steepest inclination. However, Wohlgemuth et al. report, also in the desert ant, that speed was reduced in both their uphill and downhill channels (+540 ) compared to their flat channel, thereby excluding metabolic cost as a reliable means to gauge walked distance on various inclines [28]. In an attempt to determine the effects of inclination on the gross metabolic cost of locomotion in leaf-cutter ants, Holt & Askew report that ants travelled the fastest on a horizontal plane, and indeed moderated their speed with the inclination, both on the incline and the decline. They suggest that ants adapt their behavior so as to keep their metabolic rate constant despite changing mechanical demands.

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