The hunters represent the savagery of the breakdown of the boys’ civilization.
When the boys first land on the island, they attempt to maintain order and form a system of government that mimics civilization. They elect a leader, Ralph, and decide to build shelters and start a signal fire. However, the breakdown begins right from the beginning. This is because from the start there are two factions: Jack’s and Ralph’s.
Ralph is only chosen leader because he is the one who blows the conch, which he finds and blows because Piggy tells him to. This imbues him with a kind of mystic power that causes the other boys to see him as special. From the beginning, Jack is a threat to his power. Jack already has a following in the choir. He also already has leadership skills. He insists that he should be chief because he is choirmaster, but he is voted out.
Jack might have leadership skills, but he has a savage side. This is hinted at by his reaction to the idea of having rules, and punishing those who break them.
Jack was on his feet.
“We’ll have rules!” he cried excitedly. “Lots of rules! Then when anyone breaks ’em–” (Ch. 1)
As soon as the hunters begin hunting, they start chanting about killing pigs and cutting their throats, and soon they are painting their faces and doing war dances. They descend more and more into savage and primeval uncivilized behavior until they break off from the group entirely and the rest of the boys join them. They do not build shelters and maintain civilization. Instead, they fulfill their base desires.
Jack’s savagery is further demonstrated when he is seen tying up boys and beating them for what seems to be little or no reason.
The chief was sitting there, naked to the waist, his face blocked out in white and red. The tribe lay in a semicircle before him. The newly beaten and untied Wilfred was sniffing noisily in the background. (Ch. 9)
In the end, this savagery results in the death of both Simon and Piggy. The end of civilization is complete. The boys began by trying to mimic civilization, and in the end they found themselves destroying each other completely. This is represented by the hunters and the choir.