Wasp nest building simulator by Sylvain Guérin:

A simple simulator to implement stigmergic behavior A video is also there.

More about it: Bonabeau, E., Guérin, S., Snyers, D., Kuntz, P., & Theraulaz, G. 2000. Three-dimensional architectures grown by simple "stigmergic" agents. BioSystems, 56: 13-32.