A single ant follows two rules on a grid of black and white cells: turn right on a white cell and flip it to black; turn left on a black cell and flip it to white. From this trivial ruleset, extraordinary complexity emerges.
Langton's Ant is a two-dimensional Turing machine that demonstrates emergent complexity: after ≈10 000 steps of apparent chaos the ant spontaneously builds an infinitely repeating diagonal 'highway'. No blueprint exists — order arises purely from local rules.
Press Play to watch the ant roam. Try Multi-Ant mode to see several ants interact, and explore Turmite rules that encode more complex behaviour. Speed slider controls the steps per frame.
Chris Langton introduced the ant in 1986. Despite decades of study, it is still undecidable in general whether any multi-colour ant ever builds a highway — a tiny taste of computational irreducibility.