whatAn ant colony finds the shorter of two roads between its nest and food, with no ant knowing either road exists. Drag to build walls and the traffic reroutes.

whyAnts solve routing problems with scent alone, and their trick became a family of computer algorithms. It shows how a crowd computes an answer that lives in no single head, written into the ground as it walks.

howThe ground holds two evaporating scents. An ant leaving the nest lays nest scent and follows food scent; an ant carrying food does the reverse. Each ant senses three points ahead and turns toward the strongest, with a little wander. Both roads get found, but the shorter one completes more round trips per minute, so its scent is renewed faster, and the colony converges on it. Hatching shows the scent fields; cross hatching is a road worked both ways.