Free You Are Here by Colin Ellard Page B

adjacent alleyway that also contained stripes, but of a different width. When the ants were released in the second alleyway, they would attempt to run back toward their nests. If they were using optic flow, manipulating stripe width should have caused them to make errors. Thinner stripes onthe homeward journey should have made them stop running too soon and thicker stripes should have made them run too far.
    Although this was exactly the result that Wehner obtained, it was not the end of the story. Ants that had the lower parts of their eyes covered with black paint so that they couldn’t see the ground still ran accurately to the nest. So it looks as though optic flow
can
influence perception of distance in ants, but they can calculate distance even when they can’t see optic flow. In a way this makes good sense: in their natural setting, running along salt pans in the desert, there would probably be little visual texture on the ground, and so optic flow information might not be prominent.
    A third possibility is that ants count their own steps. Wehner tested the “ant odometer” hypothesis by both lengthening ants’ legs by gluing tiny stilts to them (made of pig hair, in case you’re wondering) and shortening them using, well, scissors! Ants whose leg lengths were altered in this way made predictable errors in nest homing, suggesting that these tiny creatures do, indeed, count their steps to find their way home.
    If ants count steps, they do so in intelligent ways. In another experiment, Wehner trained ants to run over a steep hill to reach a source of food. On the homeward trip, the hill was removed. If ants simply counted steps, one would predict that they would run much too far on the homeward leg of the trip, but this is not what happened. Somehow, the ants were able to correct for the change in altitude, arriving safely home after having run just the right distance to the nest. How do the ants keep track of ground distances while traveling over hills? As Rüdiger Wehner says, this is a mystery whose solution “remains to be unraveled.” 6
    Before we move on to consider the path-integrating abilities of beings less capable than ants, we should get an idea of the precision of path integration in ants. When the ant completes a foraging runand makes a dash for home, how accurate is it? A typical foraging run carries an ant to a distance of about 200 meters from home. It travels over a meandering course of at least twice that distance before it finds food. At this point, it turns toward home in a path that intersects the outbound path several times but for the most part takes the ant across territory that it has never encountered before. Though the path is not perfectly straight, there is no suggestion that the ant pauses to search for the nest entrance until it is within about 1 meter of home. Using a generous estimate of 1 centimeter for the body length of an ant, this suggests that path integration as used by ants can yield accurate fixes on the nest from a distance of at least 20,000 times its own body length. Translating into human dimensions, using an estimate of 1.8 meters for the height of the average human, an equivalent feat would be to conduct accurate path integration from a distance of about 36 kilometers, a bit less than the length of a marathon. Try to imagine being able to walk in a meandering course, changing directions randomly, for a distance of about 70 kilometers (at a brisk pace this would probably take you about ten hours, not including time to rehydrate and nurse blistered feet), perhaps tackling a few craggy 400-meter peaks along the way. At the end of the walk, without using visible landmarks and without being able to see the point at which you began your walk, imagine being able to turn toward home with a precision of less than 10 degrees. To equal the performance of the ant, you should also be able to estimate the distance to home to within about 200 meters.

    As far as we know, no other