Ok, the research is in; we now know that ants seem to be able to count. From the London Telegraph I found:
"A bizarre experiment that involved putting ants on stilts has demonstrated that they count paces to measure distances. Researchers know that desert ants use light cues from the sky to orient themselves on their journeys back to their nests but how they determine exact distances has been uncertain."
"Drs Matthias Wittlinger and Harald Wolf at University of Ulm, Germany, and Prof Rudiger Wehner in Zurich, altered the legs on a group of ants to test the idea that they use stride length."
"Some had pig bristles glued on to their legs, while others had legs shortened by amputation (Yikes, is there a society for the prevention of cruely to myrmex?). First some marched on normal legs to a feeder, where they were placed on stilts and sent home. The stiltwalkers misjudged the 10-metre distance back and overshot the nest entrance.When the experiment was repeated with the short-legged ants, they reached their goal too early, the scientists report today in the journal Science."