So now big black ants have gone into high gear, trooping across the patio dozens at a time from one 'flower bed' to the other. Apparently I disrupted their cochineal farming or something.

After some web research, I am inclined to try diatomaceous earth. I don't want to spread poison around and the DE is harmless stuff. I considered live and let live, but it just gives me the creeps when there are constantly bugs streaming across the patio, and I have to wonder if the little dears are under my foundation, too. A million acres of open land, I just feel they need to resettle somewhere else.