They're blood-red and have 6 legs and a pair of antennae (or maybe 8 legs, not sure). I popped one of them, and they don't have any red blood inside them, so I'm pretty sure they're not parasitic (or at least not blood-sucking). It has a pretty big abdomen, and this is like the third or forth I've found. I'm in NYC, and they are about half the size of a centimeter.

I found one on the sink, and the three others around it, on the floor and by the tub.