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