Facts:
An ant brain has about 250, 000 brain cells.
The ant brains consisted of sets of thresholds for each color, as well as rules for changing their thresholds according to shifting demands, with the parameters for those rules evolved by a genetic algorithm.
Sources:
http://www.lingolex.com/ants.htm
http://www.its.caltech.edu/~mcampos/research.htm
Conclusion: Ants have a brain.