Ants can dig and tunnel out corridors when there is an anthole on the level, eventually turning the whole level into an anthole-like network of corridors. The tunneling AI prioritizes connecting up existing corridors rather than just destroying rock indiscriminately.

Ants can dig tunnels in rock (slowly).

Rock moles (and other tunneling monsters?) can’t eat through wooden doors.

Carpenter ant, which eats wooden items on the floor and can tunnel, but only on wooden terrain (doors, trees).

Burrowing monsters that don’t actually dig out tunnels (or phase), but instead move through solid rock non-destructively. They ‘‘only’’ move through solid rock; they won’t move into wall spaces or move into corridors or rooms of their own volition.

If you have autodig enabled and a digging-capable pet is next to a wall or rock square you move into, it will dig that square out for you.