By studying army ants — as well as birds, fish, locusts and other swarming animals — Dr. Couzin and his colleagues are starting to discover simple rules that allow swarms to work so well. Those rules allow thousands of relatively simple animals to form a collective brain able to make decisions and move like a single organism.
Deciphering those rules is a big challenge, however, because the behavior of swarms emerges unpredictably from the actions of thousands or millions of individuals
One of my favorite spectacles of nature, which I witnessed once while in England, is the majestically mesmerizing sight of starlings in flock. (I usually use them as a metaphor when trying to explain/convince people that individual parts, collectively, can create extroadinarily complex looking wholes)
Here's a video on youtube of starlings in flight (which, as Dave Barry would say, would be a great name for a rock band). Enjoy: