One exterminator told me that, when a nest population is dwindling, they tend to go for protein-based bait and will bypass the sweetly Terro or Pic borax liquids.
I bought one bait trap that was supposed to have 3 or 4 different types of baits. The ants would not even go near it.
I do keep some Terro/Pic cards on the kitchen windowsill for when they show up. I usually have 2-3 infestations about every 2 years.
That’s a good point: Terro will usually kill most of the colony, but often the ants will be back in a couple weeks or months. I try to hit ‘em hard: Ie., wait for the ants to show up in numbers, then put out several Borax / sugar water bait stations, with lots of bait. Otherwise, I think sometimes the queen survives. Or, maybe a new colony takes over the old one’s home.