Well, who or what is The Lord of the Flies in the first place? After all, it's the title of the novel. Surely it must play a central role in the tale.
And what a tale it is: it is an allegory, a story that tells another story. It is a story of a group of boys marooned on an island at a time of catatrophic war. The adult world is in the age-old process of self destruction, and these children on the island are re-enacting that ancient dance of death. Every motive in the adult world is there on the island with the boys. Within the boys. All that was needed was time and fear and human nature.
Simon has found the head of the recently and savagely slaughtered pig in the forest. Simon sits transfixed. The head, with the indifferent, sated flies buzzing about it is a testament to fear and survival and to our all-too-human propensity for gore, pleasure and violence.
At last Simon gave up and looked back; saw the white teeth and dim eyes, the blood—and his gaze was held by that ancient, inescapable recognition.
Yes: ancient as life and inescapable as violence and death.
“Fancy thinking the Beast was something you could hunt and kill!”
So says the Lord of the Flies. How can one kill what is part of one's own nature? Might as well try to kill your thirst or need to sleep or to breathe or breed.
“You knew, didn’t you? I’m part of you? Close, close, close! I’m the reason why it’s no go? Why things are what they are?”
It is the heart of darkness deep in our own beings.
Like Kurtz of Joseph Conrad's "Heart of Darkness," who faces depth of his own evil and utters the cry, "The horror! the horror!" Simon, too, confronts what Shakespeare's Marc Antony termed "the evil men do" when he peers into the face of the beast. Faced with this inherent evil in man Simon is overcome so much that he has a seizure.
Prior to his seeking sanctuary in his secluded spot, Simon has taken the couch and has attempted to speak to Piggy and Ralph, but he becomes incoherent; consequently, he leaves and comes upon the pig's head on the spear:
Even if he shut his eyes the sow's head still remained like an after-image. The half-shut eyes were dim with the infinite cynicism of adult life. They assured Simon that everything was a bad business.
Simon speaks aloud to the beast, "I know that," acknowledging the inherent evil in men, and that the situation with Jack and the hunters has escalated to anarchy. This recognition of "the evil men do" is what Simon has tried to communicate to Ralph and Piggy. The manifestation of flies denotes Beelzebub, confirming Simon's intuition that the boys are being overpowered by evil.
"Simon looked up, feeling the weight of his wet hair, and gazed at the sky." Like Kurtz of Conrad's novel, Simon feels the weight of the knowledge of evil upon himself. Symbolizing his oppression of spirit and subjugation to the evil side of man, the flies
tickled under his nostrils and played leapfrog on his things....At last Simon gave up and looked back...and his gaze was held by that ancient, inescapable recognition.