The following response is from a colleague Jean N. a Master Gardener specializing in invertebrate pests.  You are receiving a valuable resource which should help you deal with (solve?) this problem and navigate the crowded and often dubious world of pest control specialists that abound with all types of promises.  

"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 such as Terro, or a gel formulation with fipronil, such as Combat. 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 takea 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.”

- Odorous House Ant http://ipm.ucanr.edu/TOOLS/ANTKEY/odorous.html

- Ants (A more extensive document which includes several brief videos and various management techniques.) http://ipm.ucanr.edu/PMG/PESTNOTES/pn7411.html#IDENTIFICATION

- Selecting a pest control company http://npic.orst.edu/pest/selectpco.html