I found Ant City. Well, this morning I found a small ant. Over the last few days, I've caught a few large ones crawling around the kitchen. This morning, I found a small ant, as I said, on my foot.
The ants had apparently discovered a small piece of an onion skin, and they apparently liked what they found.
Forensically, I suspect they followed the phone cord in from outside before taking the more formal approach and entering through the door.
I took most of them outside before resorting to vacuuming up the stragglers. The basket of grocery bags is waiting out on the deck for me to decolonize it.
The vacuum may have been a traumatic experience for the ants that didn't make it back outside, but I'm not sure if they got the message. As I write this, I see ants coming back in the door.