Many insects are known to navigate between their home and feeding sites with remarkable precision. This is also the case for the desert ant Cataglyphis fortis, which navigates in the vast and largely uniform Sahara desert by continuously keeping track of the direction and distance to their nest. This is a process known as path integration, which allows them to take the direct route home once they have found food, instead of following the sometimes tedious route used during their outbound search. While it has been shown that these ants use visual cues from the sky to keep track of the direction they have taken, less is known about how they judge the distance needed to return, but it seemed certain that they must use an odometer.

There are several hypotheses that could explain how their inbuilt odometer works but the most likely is that they assess distance by a step integrator (a pedometer) that in some way keeps track of how many steps they use. However, this hypothesis had not been tested until a group of scientists from University of Ulm and University of Zürich examined what happened to the ant's sense of distance when their legs were artificially shortened or lengthened.

The group trained ants to travel along a straight 10 m channel between the nest hole and a feeding site, so that the ants walked directly to the feeding site and collected a food item before turning around and heading home. When the ants were caught at the feeding site they remembered the direction and distance to home for a considerable time afterwards. So their idea of distance could be tested by placing them in an adjacent channel, without a nest hole, and measuring how far they walked before beginning to search for their `fictive' nest. In this experimental setup the group showed that `control' ants walked an average of 10.2 m before searching for the nest hole. The group then examined what happened when ants had their legs shortened or lengthened artificially before starting the homebound journey, and found that the ants misjudged the distance to their nest considerably when their stride length was manipulated.

One group of ants had their legs elongated by gluing pig bristles to the legs and these overshot the distance by approximately 5 m. Another group had their legs shortened by severing the outer part of their legs, and this group undershot the distance by more than 4 m. This strongly indicates that the ants use a `step integrator' to gauge distance. To validate this the group assessed the number of steps taken by control ants and multiplied this with the relative change in stride length of ants with shortened or elongated legs. Indeed, when stride length was corrected for body size and walking speed the expected/calculated distance travelled was very close to that observed for ants with elongated or shortened legs, confirming that they use some kind of `step counter' to measure distance.

Although ants probably do not `count' in a conventional sense they must be able to continuously keep track of how many steps they have used on their way out. Thus, when ants with manipulated legs took the outbound route from the nest to the feeding station with their `new' legs, they returned at the right location, since they `counted' the right number of steps on the way out.