S. Goss, J. L. Deneubourg, R. Beckers, and J. Henrotte. Recipes for collective movement. In Proc. European Conference on Artificial Life, pages 400-410, 1993.
All of members of the little swarm in the simulation continuously send out an undirected signal. They also have a sensor in the front, to the left and to the right. There are a few variations on the rules that regulates movement, but the basic idea is that if the signal recieved with the front sensor is strong enough it will continue to move forward , otherwise it will turn left if the left sensor receives the strongest signal and turn right if the right sensor receives the strongest signal.
By varying the parameters it is possible make the swarm to behave in quite different ways.