Route Formation and the Choreography of Looking Back in Desert Ants (Melophorus bagoti)

Abstract How ants, wasps and bees rapidly form visual routes represents an enduring mystery as well as a powerful example of the abilites of insect brains. Here, we analyse a previously uncharcterised behaviour, ‘lookbacks’, underlies rapid bi-directional route learning in desert ants. During these lookbacks, foragers stop forward movement to their goal location, turn and fixate their gaze to their origin, often for only 150–200ms. This turn appears to be a critical period for learning the inbound route. Route formation relies on acquiring visual cues and comparing panoramic view memories with the current view. While the nest panorama is learned during pre-foraging learning walks, during which naïve ants often fixate their gaze at the nest, route following requires separate behaviours to learn route based views. We untangle how route formation occurs in naïve Melophorus bagoti foragers during the first foraging trips by focusing on the previously uncharacterised lookback behaviours and their function in facilitating visual learning. Lookbacks were highly associated with the first few foraging trips and were concentrated in areas where the visual scene changed rapidly. Analysis of gaze directions during lookbacks show foragers clearly fixate their view to the nest direction during these behaviours (or alternatively to the feeder during inbound homing), learning the nest-aligned inbound route during their first outbound trips. We discuss lookbacks as a ‘when to learn signal’ combining visual rotation and gaze fixations to produce view-based route following.