Guillermo Del Torro interview

Del Toro puts much thought into the monsters that he creates. He takes concepts from visual art, literature and his real life experiences. Sometimes he uses concepts that he received from dreams or even just ideas that pop into his head. At times he would use Real life creatures for example one of the creatures in Pan's labyrinth was based off of the manta ray. Some creatures were based on insects because insects have strong exoskeleton causing them to in some ways mirror warriors. This gave them a sort of poetic strength. Also, in The devil's backbone the monster always appears in front of the children and no one else because when he was younger he would always see a monster in a lucid dream so he for a long time thought that monsters were real. Which he later in his life was quoted as saying that this is part of what let him keep his sanity.