p.s. they are not the kind of millipede that curl up into a ball. They're longer than those. They're moseying about, moving pretty fast but not running like centipedes do.

You should do a google image search and figure out what these are. I can never remember the difference between centipedes and millipedes, so I googled it:

'Centipedes are beneficial in the garden because they prey upon other insects. Millipedes are fine in the garden, since they mostly eat rotting detritus.'

If you have millepedes in a second floor, you might have a serious problem with moisture behind the walls or under the roof somewhere. If I found these in my house, I'd want to do some scouting to find out what they might be eating.

Good luck - I know how creepy it is to find insects in your house! We recently had a problem with a light timer that was supposed to control the light at the front door. When the electrician took it out of the wall, the whole switch area was full of tiny ants. I still can't touch that switch without thinking about what might be behind the wall.

Yuck. I had a spate of two inch long hairy insects in the upstairs: a wall in one room, a couple in the bathroom sink. I mean you could see these critters across a 10 wide room. One gets sensitized to these things.
This reminds me of the "waterbugs' in my grandmother's kitchen in New Orleans. It wasn't until I was an adult I realized they were roaches...maybe palmettos; in any case they were at least two inches long and scurried around the kitchen floor when you turned the lights on. To this day I don't enter any kitchen until I've turned on the lights and waited for the (non existent) roaches to run away.

I just found more millipedes in the house, one year almost to the exact day I found so many last year! So far only a few, but I'm bracing myself to find more. They are on upper floors again, in bedrooms not bathrooms, so still no idea how they're getting in. I guess it's related to hot, humid weather. I thought I'd update my post from last year to see if anyone has had a similar experience.

Grossaroo. We get big black ants in the spring/summer, mostly in the bathroom because they like the moisture. And don't get me started on the house centipedes...... *shiver*

Jw - careful. The big black ants may be carpenter ants. This is definitely the time of year they are active.