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Abstract

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.