It took a while, but we finally found what these particular ants love to eat. It's salmon. I took an old salmon can (I'm sure tuna would have worked too), sprinkled in a decent amount of borax powder (cheap, and available at hardware stores in the laundry area), I placed another can on top of it (because it started stinking). You could use an old lid with a hole in it, or aluminum foil — whatever lets them in. If all goes as planned, they will carry the salmon and borax residue back to the nest, and it will wreak havoc in there.