Just Like Buffy

As I'm finishing Leviathan, I can't help but make the comparison to an old episode of Buffy the Vampire Slayer (any fans out there?). In the episde Bad Eggs (really sad that I know the name of it) all of Sunnydale's residents are taken over by a parasite which is part of a larger monster. They are taking away rocks and part of the basement flooring to eventually free the monster. Wonder which came first: the Buffy monster or the idea for Leviathan?