Who are the Intruders?

One way to read Searching for Intruders is as a novel of stories.

How do all of the stories relate back to the title?

Is the search for the intruders ever complete or successful?

Who are the intruders?

In the first story, "Roaches," it seems pretty clear that the intruders are the cockroaches. And yet, as anyone who has ever rented a New York apartment knows, the roaches were there first. (But of course they don't pay rent.) What keeps intruding on the relationship between Wilson and Melody?

Keep reading the stories with these questions in mind. See if you can detect a subtle thematic organization here.