Visual discrimination of shapes in the ant Myrmica rubra (Hymenoptera, Formicidae)

Using collective differential operant conditioning, it could be shown that workers of the species Myrmica rubra distinguish different filled shapes of similar size (e.g. a black square from a black circle, a black triangle from a black circle, and a black triangle from a black square). They are unable to discriminate hollow shapes (e.g. a rectangle from an ellipse, or a lozenge from an ellipse) of similar size. When presented with hollow shapes, M. rubra workers rely more on the length of the perimeter than on the actual shape. A hollow lozenge and rectangle of identical height and width but with a different perimeter can be partly distinguished; hollow shapes of different height and width but identical perimeter are not at all discriminated. The visual perception ability in M. rubra is weaker than in M. ruginodis but superior to that in M. sabuleti; this assessment is consistent with the eye morphology and the navigation system of the three species.