Books exploring the topic of stigmergy and related topics such as "complexity" and "complex adaptive systems"
Resnick, M. (1994). Turtles, Termites, and Traffic Jams: Explorations in Massively Parallel Microworlds. Cambridge, MA: MIT Press.
Sync: The Emerging Science of Spontaneous Order by Steven Strogatz
How Everything Is Connected to Everything Else and What It Means by Albert-Laszlo Barabasi
Emergence: The Connected Lives of Ants, Brains, Cities, and Software by Steven Johnson
Six Degrees: The Science of a Connected Age by Duncan J. Watts
At Home in the Universe: The Search for the Laws of Self-Organization and Complexity by Stuart Kauffman