"Now he says it was a beastie."
"A snake-thing. Ever so big. He saw it."
"In the woods" (Chapter 2).
In Lord of the Flies, the boys' nameless fear shifts into the horrible shape of the Beastie; it becomes the sum of all the things that frighten them about the island: the unknown, the dark, snakes, the woods, shadows, creepers, scary noises. Without any adults there to comfort them, the littluns' fears run wild, and their nightmares become terrors. Ralph understands the importance of taking the littluns' fears seriously, unlike Jack who is quick to dismiss them as 'baby talk.' The Beastie represents the early representation of the boys' fear on the island, a fear that will grow so great that it ultimately causes them to overreact and murder Simon.
The 'Beastie" epitomizes the boys' fears. It is symbolic of their childhood nightmares, their worst fears. The boys are on an island sans adult supervision. They feel vulnerable and have been traumatized by their experiences thus far.
This is especially true of the littluns who feel the most unprotected. The older boys do not care much about them and the lack of caring and nurturing frightens them even more. The little that Ralph and Piggy offer is not enough to make them feel comfortable. They feel isolated. They need guidance and are not getting any.
In moments of extreme anxiety, the littluns turn to that which they know to provide at least some sense for their dilemma and, unfortunately and ironically, since there is a lack of anything else, all they can cling to is that which they fear.
The Beastie becomes the prime focus of the boys' fears, the dread of the unknown, of the real and imagined dangers of life on this lonely island. The use of the word, 'beastie', rather than 'beast', at this point also emphasizes the fact that this fear takes shape first of all among the youngest of the boys, the 'littluns'; this term has a very childish ring to it. However, the fear will not stop there; it will end up infecting all the boys, except the curiously wise and detached figure of Simon, who is able to see past the emotions of the others. Even the sensible, level-headed Ralph and intellectual Piggy are not immune to irrational fears.
It is also significant that the beastie is first of all described as being a 'snake-thing'. The image of the snake, or serpent, has loomed large in many cultural traditions as a source not just of fear but of an active evil. This foreshadows what will happen on the island, when many of the boys, led by Jack, end up giving free rein to their basic instincts of war, savagery and bloodlust.
Of course, there is no physical, monstrous 'snake-thing' on the island that threatens the boys, but it comes to function as a metaphor for the darkness that lurks within the boys themselves. The real danger, the real evil, is not an external force but internal, and a seemingly ineradicable part of human nature - something that not even supposedly rational adults can get rid of. After all, it is all-out atomic war, a spectacle of global destruction conducted among their elders that is responsible for the boys being left alone on the island in the first place. It might be said that in the world of this novel the beast comes to reign supreme.