I have been bothered by indoor ants throughout the year. They will come into the kitchen on the counters and underneath the sink and a bathroom on an outside wall. They also get in to a bathroom on the same wall without a window. I have drawn a line of Diatomaceous Earth around the foundation of the house and it pretty much has taken care of the problem. This morning the sink in the windowless bathroom was completely black with the ants. I sprayed them with a pesticide and cleaned it up. Several hours later there was a 'swarm' of them around the base of the toilet.
More than likely, you are beset by odorous house ants, small black fellows which are perhaps the most common household nuisance ants in the northwest. Unfortunately, their lifestyle helps them avoid human attempts to get rid of them. I have them, too; they came with the house when we bought it 5 years ago. I’ve learned that I must have commercial ant bait at hand so that I can set it out shortly after the little beasts come indoors. Triggers for such “invasions” appear to include heat spells, cold spells, and heavy rain. And, as you know, crumbs.
The most effective commercial baits for home use against odorous house ants are those with a boric-acid base product, or a gel formulation with fipronil. If those materials don’t produce the results you want, consider hiring a pest control company as they have products unavailable retail. Such baits are specially formulated so that the foraging ants take the Material home and, then, share it with family and friends.
I encourage you to stop using diatomaceous earth (DE) indoors as it is an inhalation hazard. Also, don’t ring the foundation with DE because, at least some of the ant nests are under the house, in which case, you have limited their hunting grounds to your indoor spaces.
Likewise, don’t spray indoors, as that also risks your health. Beyond that, it kills less than 10 percent of the ant “armed forces.” Here are some resources: