I found a few of these walking in the middle of the night (about 3 AM) on a wall in my room near the floor. They are at most a few millimetres long (no more than 2 I would say). I am living in Poland, in a block of flats.
EDIT: Since I first wrote, I have seen few more - very small - less then 1 millimetre long. They seemed to be coming from behind the baseboard. This time I've seen them during daytime.