Aggressive conflict used as landmark information in homing desert ants.

Across many species of the animal kingdom, the ability to navigate long distances is important for securing food and other resources. For example, ants, bees and rats have long been known to use path integration, a mechanism to integrate distance and direction travelled, to find their way back to their nest. However, path integration is imperfect, and errors accumulate over time as animals forage. There are several ways to counteract this uncertainty, for example by utilizing local olfactory or visual landmarks along a familiar route to infer an individual's position relative to its nest, i.e. its homing vector. Local landmarks are thought to be effective if they are constant, granting a strong association with the discrete location at which they are located. Here, we showed that ants can utilize something much sparser and more distributed than an individual constant landmark to inform its homing vector. Our data suggest that Tunisian desert ants integrate intraspecific contact, or social cues, to augment navigation. Although exposing homing ants that arrive at their expected nest position to colony members has no effect on their subsequent nest-search behaviour, contact with foreign conspecifics at a position where the nest is expected diminishes path integration certainty, thereby expanding the nest search pattern. Furthermore, we showed that ants form associations between intraspecific conflict and discrete locations to create so-called local vectors, within which the homing path to the nest can be stored. Apparently, ants remember aggressive interactions and take them into account when navigating.