What is the theme in The Wasp Factory: A Novel by Iain Banks?

Murder is the main theme of the book. "The Wasp Factory" is the story of Frank Cauldhame, a sixteen-year-old mass murderer. The story begins to reveal early on that Frank kills and mutilates animals. He has dozens if not hundreds of animals skulls hidden away in a secret bunker. He has a bag of animal heads and body parts that he carries around with him. He affixes the severed heads of small animals atop long poles located around the small island where he lives.