Thursday morning... that one egg hatched as soon as I put up the capsule of Boric Acid in my anus. Maybe it triggered it to hatch early. Anyway, I dusted the anal opening where the intense itching was with Boric Acid powder, using the duster. A just hatched nymph is very hungry: bites the finger if I put it there... I have learned my lesson.
Just one more thing before I forget: Boric Acid, I read, is not toxic for humans. So I will test it by taking boric acid capsules orally... Wish me luck.
If that works, then we've licked the nymph issue... but still the adult spider mites issue remains.
A few months ago I tried Insect Growth Regulator on my floors, and it seemed to have worked... on the adult mites... but not enough so that I would have licked the infestation.
So the search is still on.