Phobic responses of bull ants (Myrmecia midas) to odours introduced on their foraging route.

Goal-oriented learning and navigation is well known in eusocial insects. The solitary foraging of nocturnal bull ants Myrmecia midas in their visually complex environment relies on path integration and landmark learning. While this species seems to be 'sensitive' to handling and reacts to visual changes in their surroundings, not much is known about how added olfactory stimuli impact their route navigation on a vertical surface. In the current study, we added one of five different invisible odours on the trees on which foragers normally forage. We found that the bull ants showed phobic responses to all the odours. The Tea-tree and Lavender odours showed the strongest impact on the bull ants' navigation by causing detours, U-turns, and avoidance of the sensory stimuli, with the ants meandering more and scanning more frequently. The odours of Olive oil, Flax-seed oil, and Eucalyptus oil had a moderate impact on the ants' navigation. These findings showed the widespread influence of non-visual chemical cues in shaping bull ant navigation, reactions that we interpret as neophobic responses stemming from chemical alterations on learned routes. A second experiment supported the interpretation of neophobia as opposed to an inherent aversion to the odours. Repeated exposure to Lavender led to reduced aversive responding. Overall, this study contributes to the understanding of the effects of foreign odours, adding to our understanding of the complex learning processes of bull ants in their vertical navigation.