Stigmergic Swarm Construction (2D)

This top-down version makes the "no map, no radio" claim easy to check with your own eyes: each robot's whole world is the cell it is standing on and its four immediate neighbours. It reads the local pheromone level, runs it through a response-threshold rule, and either places a block or doesn't — that single local decision, repeated by every robot independently, is the entire construction program. Placing a block deposits more pheromone on that cell, so the next robot to wander past is more likely to build there too, and that closed loop of build → deposit → sense → build again is what turns a flat empty grid into a field of discrete towers with zero central planning. Hit "New random start" to reseed the colony with a different robot count and different starting positions — the local rule is unchanged, and the towers that grow back settle into the same characteristic spacing and height distribution every time, which is the hallmark of genuine stigmergic self-organization rather than a scripted layout.