Ants’ searching behaviour can be biased by recent experience of familiar scenes: a newly observed interaction between innate strategies and learnt information

Ants can use multiple sources of information to navigate, but do not seem to integrate all this information into a unified representation of the world. Rather, the available information appears to serve three distinct navigational systems: Path Integration, systematic search and the use of learnt information, mainly vision. There is a strong tradition of interpreting ant behaviour as resulting from simple interactions between these independent strategies. However, here we report on a newly observed behaviour which suggests a sophisticated interaction between the components of an ant’s navigational toolkit. We enclosed an ant nest so that the only foraging location was along a narrow 8m “road” to a permanently stocked feeder. Returning ants could be captured at precise locations, so that we had control of the current state of their path integration system, i.e. how far did the ants think they were away from the nest. These ants were then released on an unfamiliar test ground, where there initial headings were recorded. Ants captured close to the nest, so that they had run-off their path integrated vector, did not show the undirected headings we would expect of ants entering into a systematic search. Instead, these ants backtracked in the direction they had just travelled. Interestingly, ants that ran off their Path Integrated vector by being forced to run the first 4m of the route twice, did show undirected headings characteristic of systematic search. Therefore, we see that only ants that have recently seen the familiar visual surrounds close to the nest, will backtrack when placed in unfamiliar terrain. The ecological function of such behaviour is clear, as it increases their chance of returning to familiar terrain. What is interesting is that the decision-making process requires sophisticated interactions between navigational systems. It involves the compass system modulating the initial direction of the search when in unfamiliar terrain on the basis of the recently experienced familiar view. This raises fundamental questions about the cognitive architectures underlying ant navigation.