The experiments were such that the ants couldn't just communicate by leaving behind a scent trail, I believe. In order to alert other ants to the location of food, "presumably they (other ants) may pass messages not about the number of the branch but about a distance to it or about the number of steps and so on," the scientists write.
"Even if it is so," they add, "this shows ants as being able to use quantitative values and pass the information about them." Other research shows that both ants and bees perform "abstraction, extropolation," and other math skills, the researchers note.
Ants, they continue, can "perform simple arithmetic operations with small numbers. We suggest that applying ideas of information theory and using the natural communication systems of highly social animals can open new horizons in studying numerical cognition."
The scientists additionally highlight other studies demonstrating math abilities in various animals. Birds usually ace math, with pigeons, crows and parrots being particularly good at number-related puzzles. (Although my guess is this talent must carry over to other birds. These three birds may just be easier to study.) Non-human primates, such as chimpanzees, do OK at math, but ants may be even more precise.
If only ants could be trained to do taxes!