Fig. 7. Search density distribution of ants that faced different types of landmark stimuli. Ants were trained with a black and rough landmark at the nest entrance (black square) and later tested with a landmark of different properties defining the nest entrance at 7.5 m (red square, LM-position). Test 2A (shaded area): Control experiment with a black and rough landmark (same experimental situation as test 1B, but new data set). Test 2B (thin solid line): a grey and rough landmark deprived the ant of the visual contrast. Test 2C (broken line): a black and smooth landmark changed the surface roughness, but left the visual contrast intact (as compared to the training situation). Test 2D (dotted line): the lower hemispheres of the ants' eyes were covered with lighttight paint depriving the ant from any visual cues from below.