How is the Lord of the Flies like a devil in the novel?

One powerful literary device that William Golding uses in Lord of the Flies is the Christ-figure. Simon, the most sensitive of the boys and the only one who understands the deeper truths about "mankind's essential illness," acts as a Christ-figure. Many works of literature that contain a Christ-figure use a devil figure to reinforce the role of the Christ-figure. That is part of what Golding does with the sow's head that becomes the Lord of the Flies in Simon's vision. Several parallels to the biblical devil are apparent.

First, the devil has delusions of grandeur. In the Christian tradition, Lucifer, a being that most people believe is Satan, declares "I will be like the Most High." Thus the body-less pig has the grand title "Lord of the Flies" and claims to be "the Beast," although Simon names it for what it is: "Pig's head on a stick." "Lord of the Flies" is the translation for "Beelzebub," considered to be the chief demon or Satan himself.

Second, the devil seeks to torment those who have a special calling in their lives. Jesus said to the Apostle Peter, "Satan has desired to have you that he may sift you like wheat." The Lord of the Flies says many things to torment Simon, telling him that the other boys think he's batty, that there isn't anyone to help him, and that "we shall do you." 

Third, the devil seeks to prevent the Christ figure from fulfilling his mission. Jesus was tempted by the devil for 40 days in the wilderness. The devil tried to get Jesus to worship him and to do things contrary to his mission. The Lord of the Flies tries to get Simon to forget what he knows about how the "beast ... is only us." It tries to convince him that "it was just a joke, really" and says, "Get back to the others and we'll forget the whole thing."

Beyond the way it interacts with Simon, the Lord of the Flies is an embodiment of filth, representing evil. The disgusting flies crawl all over it; "the obscene thing grinned and dripped." It has the "infinite cynicism of the adult life." Golding's language makes the head the embodiment of evil, which is like the devil.

Because of the way the head interacts with the Christ-figure, Simon, and because of its association with evil, it is like the devil in Christian tradition.