Ant navigation: One-way routes rather than maps

In recent years, there has been an upsurge of interest and debate about whether social insects-central-place foragers [1] such as bees and ants-acquire and use cognitive maps, which enable the animal to steer novel courses between familiar sites [2-4]. Especially in honey bees, it has been claimed that these insects indeed possess such general landscape memories [5] and use them in a map-like way [6]. Here, we address this question in Australian desert ants, Melophorus bagoti, which forage within cluttered environments full of nearby and more distant landmarks. Within these environments, the ants establish landmark-based idiosyncratic routes from the nest to their feeding sites and select different one-way routes for their outbound and inbound journeys. Various types of displacement experiments show that inbound ants when hitting their inbound routes at any particular place immediately channel in and follow these routes until they reach the nest, but that they behave as though lost when hitting their habitual outbound routes. Hence, familiar landmarks are not decoupled from the context within which they have been acquired and are not knitted together in a more general and potentially map-like way. They instruct the ants when to do what rather than provide them with map-like information about their position in space.