Hello, returning newbie here. I've been absent for a few years.
I've just had a yearlong experience with carpenter ants in the house, and learned a few things about their behavior. Perhaps these tips will help others.
1. The carpenters came into the house at a time of drought.
2. Neighbor next door for unexplicable reasons piles brush on the border of our properties. I think the ants had been nesting in there. It was that side of the house where they were the most prolific.
3. I had successfully used rubbing alcohol on the tiny kitchen ants, and tried it on the carpenters. It worked, but only for awhile. I think they may have developed an immunity to it.
4. When I discovered they were in the doors, chewing away and building nests, I gave up on the rubbing alcohol and used commercial ant bait, and watched the patterns of behavior. There were different sizes of ants. First the smallest (about 1/4" in length) came out scouting, followed by the carpenters, about 1/2" in length. Then the winged ones came. They were the largest, about 5/8" to 3/4" in length. They were also the slowest moving ants.
5. Typically I killed about 5 dozen ants a day.
6. There was a bit of a lull after killing the winged ones, until I put out fresh ant bait, then the process repeated itself. I never could get rid of all of them.
7. I used a stethoscope held against the door to tell which doors they had colonized.
8. They loved the bathroom sink and bathtub, proving that they're attracted to water. They were especially active around 6 a.m.
9. After a few good rains this April, they disappeared, with no more than 3 returning over the last month or so.
10. The smaller ones reappeared in the kitchen, so I tried something else, a water, baking soda and Borax mix. That worked better than anything, killing them almost instantly. In 3 days they were completely gone and haven't returned.
11. We haven't had much rain this year, so I wouldn't be surprised to see them again, but if I do, I'll go outside and water down the brush pile next door. Maybe that will keep them outside.
I've not heard of using grits, but I might try it on the brush pile. At least it wouldn't hurt any animals that wander by.