Scientists look at how ants dig tunnels, and come up with some surprising results. Slip beneath the surface and the above-ground simplicity of an ant hill gives way to subterranean complexity. Tunnels dive downward, branching and leading to specialized chambers that serve as home for the colony’s queen, as nurseries for its young, as farms for fungus cultivated for food, and as dumps for its trash. These are not just burrows. They are underground cities, some of them home to millions of individuals, reaching as far as 25 feet underground, often lasting for decades.