At the junction of the floor and wall in both bathrooms there are gaps like this, which may be an entry. https://www.flickr.com/photos/90278919@N00/15937498515/
(Ironically, as I was taking the photo, one did emerge. But that was the first time I witnessed this.)
I want to seal the gap not only because of the ants, but to improve the appearance. My plan is to brush some borax powder into the cracks, then run a narrow bead of caulk along the crack to hide it.
The former owners had newly installed carpeting in the bedrooms, so I can't see if they have similar gaps, but I can put borax acid along the outside edges.
Any other ideas?