sumisu: maybe, you and I are on the very cusp of an interesting scientific breakthrough. I am actually only half-joking. No ants means no aphids. One would think that because ants can be an enemy of worms, that this situation could not exist.
Now the black ant does like to make its nest against walls, rocks, and/or under stones. I long ago removed any significant stones from my plot (although they're around as markers). Could this is the reason?