Ant colony systems are really interesting! It's fascinating how distributed creatures can communicate and, with a simple set of rules, converge on a good solution.
Last year I did a GPU programming project involving an ant-colony-like simulation. Based on the idea that ants have immediate knowledge only of their neighborhood, it's a simulation that works well with GPU fragment-shader-based parallelization:
http://www.dan.andersen.name/gpu-accelerated-3d-ant-colony-s...