Homing Ants Get Confused When Nest Cues Are Also Route Cues

The desert ant Cataglyphis fortis inhabits the salt pans of Tunisia. Individual ants leave the nest for foraging trips that can cover distances of more than 1,500 m [1]. Homing ants use path integration [2, 3], but they also rely on visual [4] and olfactory [5] nest-defining cues to locate the nest entrance. However, nest cues can become ambiguous when they are ubiquitous in the environment. Here we show how ants behave during the nest search when the same cues occur at the nest and along the route. Homing ants focused their search narrowly around a visual or olfactory cue that in training they had experienced only at the nest. However, when ants were trained to the same cue not only at the nest but also repeatedly along the foraging route, they later exhibited a less focused search around the cue. This uncertainty was eliminated when ants had a composite cue at the nest that consisted of two components, one unique to the nest and another that also occurred along the route. Here, the ants focused their search on that part of the binary blend that was presented only at the nest and ignored the other, ubiquitous component. Ants thus not only seem to be able to pinpoint their nest by following learned visual and olfactory cues, but also take into account which cues uniquely specify the nest and which, due to their ubiquity, are less informative and so less reliable. VIDEO ABSTRACT.