From an article I found online:

A team led by Matthias Wittlinger, a biologist at the University of Ulm, Germany, made modifications to desert ants [...]. After setting up an ant home outside the lab, the researchers let 25 ants take a 10-meter trip from their nest, then collected them. For one group, the team glued tiny stilts to the insects' legs. For another, they clipped the legs down to stumps. And for a control group they left the legs alone. Then the researchers gave each ant a piece of food and set it free. With morsels of food in their jaws, the ants immediately headed home. If desert ants do indeed use an internal pedometer, then the modifications should mess up their calculations.

Not only did the stilted and stumpy ants not make it home, but they also misjudged their distances exactly as the researchers predicted. The ants on stilts went about 5 meters too far before stopping to search for the nest, whereas the stumpy ants stopped about 5 meters too short [...] (Control ants got back home just fine.) After the modified ants were returned to the nest, they were able to go out and get back home just as accurately as normal ants, which should be the case if they're keeping track of the number of steps.