Learning to find a gap: navigational problem solving in nocturnal bull ants

Solitarily foraging ant species derive compass information from terrestrial landmarks and path integration to navigate. Our test ants, solitary foragers of Myrmecia midas, have the added challenge of completing their navigation during evening and morning twilight. The aim of this research was to test bull ants’ ability to use edge contrast to find a gap in an obstacle that obstructs their direct path. Ants were individually identified and tested repeatedly on their foraging trip. An artificial obstacle (0.9m by 1.2m wide) with a 10cm gap in it was installed on their foraging route to train them to find the gap. The gap location was unpredictably varied from one run to another so that the ants had to look for it. In training, each nest of ants was given two colour conditions on the obstacles: one with black on one side of the gap and white on the other side (which was easier to spot), one with black on both sides (which was harder to spot). We tested the ants’ ability to find the gap and measured the directness of the path. We found that the ants learnt to find the gap in the obstacle after completing several trials. However, we did not find any significant differences in the ants’ behaviour in the two colour conditions.