Geesh, I'm starting to sound like Craig with all of my bug talk.
I think my main source of unease (if you can even call it that - these things aren't keeping me awake at night) is that I don't know what they are, so I don't know if they present any danger to Niki. I've been keeping her out of that bathroom, but they were in there with her for a little under a week before I realized it. I know this because what I had originally thought was dirt/plant matter in the toilet (Niki goes out, lays in the dirt and weed bits, and then some of that gets in the water that she drinks) turns out to be these little bugs. Btw, I don't use that toilet and keep it clean just for Niki.
I don't know if she ever drinks out of it, though. Anyway, so she was in there with them for several hours, and she hasn't been scratching or anything. I'm sure that they've gotten on me, and I don't feel itchy. So, I doubt that they are harmful, but I'm bothered by the shear number of them. I also can't stand that I don't know where they are coming from, so I don't know how to stop them.