I keep finding these things in my New York City apartment, and I am very curious what species they are. I thought they were cockroaches at first, but couldn't find any pictures online that would resemble these insects.
(Added later):
Thanks for a comment--I am now convinced that these are, in fact, spider beetles. Mine look somewhat dissimilar to the ones shown on wikipedia--they are black in color and round in all three dimensions, they looked like balls with legs when they crawled, which totally confused me as to what those things were!