How to navigate without maps:
The power of taxon-like navigation in ants

Rodents are said to have two different navigational systems, a map-like locale system and a route-based taxon system consisting of sensorimotor routines such as beaconing and turns at appropriate stimulus conditions (motor routines). Ants on the other hand are not known for map-like navigation, and seem to get by with a repertoire of taxon-like strategies. I review how this repertoire serves ants in making up for the lack of a locale system. Path integration — keeping track of the straight-line distance and direction from the starting point — operates continuously in the background, and can be called upon as necessary, or relied on in habitats in which no useful visual cues are available. Crucial to the power of a taxon-like repertoire is using the full panoramic visual context, both to guide the operation of strategies (context-modulated servomechanisms) and to guide navigation directly. The entire repertoire is backed up by systematic search strategies. I end with some reflections on the power of taxon-like strategies.

Video Ants were trained to forage at a feeder. On exiting the feeder, they had to go through a short stretch of a narrow channel before coming out into the open. On the recorded trial, the ant with her booty in the mandibles was displaced by several meters before being released into the channel. A piece of white paper was placed at the exit of the channel, with marks for calibration, and the ant was videotaped from above. A high-speed camera was used, so that using normal playback, the action is slowed down ten-fold, making the pirouetting scanning movements clear to see. The ant might make several sets of such scanning movements before finally dashing off. Informal observations suggest that when coming upon an unusual or unexpected scene, the amount of scanning increases. Thanks to Antoine Wystrach and Paul Graham for supplying this movie.