There's quite a nice and easy to use program (a programming / modeling environment) for exploring and getting an intuition of how a system of many individuals who follow simple rules and interact with each other can give rise to interesting complex behavior. The modeling environment is called NetLogo, and it's basically a multi-turtle version of the old famous Logo programming language. It has lots of different models included in its example model library, including about ants, and the models have modifiable source code. I have quite enjoyed playing around with it, and have even used it in some presentations about how simple rules can give rise to complex behavior.