Top-down pheromone-foraging lab: ants shuttle between the nest and four food sources, depositing a decaying pheromone scalar field on a grid as they walk. Once "Trail following" is above zero, ants also steer up the local pheromone gradient instead of walking a straight line to their target — the same stigmergic rule (deposit + follow + decay) that lets a real colony converge on the shortest usable path without any ant knowing the map, made visible here as a live scalar field instead of implied.