I've previously posted on Starlings in large groups that look like schools. Again I'm going to highly recommend the last link in that post. In fact the Starlings are demonstrating swarm behavior. National Geographic has a new accessible article on Swarm Behavior.
That's how swarm intelligence works: simple creatures following simple rules, each one acting on local information. No ant sees the big picture. No ant tells any other ant what to do. Some ant species may go about this with more sophistication than others. (Temnothorax albipennis, for example, can rate the quality of a potential nest site using multiple criteria.) But the bottom line, says Iain Couzin, a biologist at Oxford and Princeton Universities, is that no leadership is required. "Even complex behavior may be coordinated by relatively simple interactions," he says.
In addition to other great example of swarm intelligence, the article also talks about some applications of this type of intelligence for human activities.
I've missed the boat a bit on this one as many other blogs have already linked to this article.