De Terlizzi says Arthur Rackham's illustrations have influenced his work.
...Arthur Rackham's imaginative quality really struck a chord within me, and his work always comes to mind when I think of an old fairy tale. That's what I wanted the Spiderwick books to look and feel like. There were beautiful things in his world, and there were grotesque things… I always keep that in mind when creating characters and a world.
Black talks about her writing and her books. She and DeTerlizzi discuss how they collaborate and some of the themes in the Spiderwick books...
Spiderwick kinda works on those different levels. There are very real problems Jared has to deal with at home, at school, and with his family. Then there are the problems he encounters in the faerie-world. The important thing here is that he does not solve them all at the end of the story. I think the ending is satisfying but it certainly doesn't tie every loose end up with a bow on it… but that's the way life is, isn't it?
I have not read all these books so I was intrigued by this exchange:
DHBks[reporter]: My nomination for the best sentence in all five of the books is this one, to be found in the fifth book: “There, lying on a carpet of corrugated metal, was a cow.” My jaw dropped. Did the two of you brainstorm that sentence – and the interesting images that ensue from it – jointly?
HB: Glad you liked that one! We didn't actually brainstorm sentences, although we went over things together many times. I'm not sure how that particular sentence evolved -- what I do remember was thinking that it was the most surreal cliffhanger I'd ever written.