Perhaps the most important rule in storytelling is that every person, place, thing, or event in the story needs to serve a purpose. If an element doesn't have some unique effect on the characters or the plot, then it should probably be removed. This rule is a lot more strict in film than in literature, but even books can only get away with spinning their narrative wheels for so long. Considering this, let's examine one of the more famous scenes from The Hobbit where Bilbo saves his dwarf companions from the spiders in the forest of Mirkwood.
Here's how the journey through Mirkwood unfolds in both the book and its film adaptations:
2. Bilbo gets separated from the dwarves.
3. The dwarves get captured by spiders.
4. Bilbo saves the dwarves from the spiders.
5. The dwarves get captured by elves.
6. Bilbo saves the dwarves from the elves.
Looking at this list, the chain of events seems a little redundant. Why not just have the elves capture the dwarves right after Bilbo gets separated from them and leave out the spiders altogether? The elves are more important in the long run, and since rescuing the dwarves from them is the bigger challenge of the two anyway, it seems like more efficient storytelling to only have one rescue in Mirkwood. So what's the point of including the spiders in the plot?
Well, the first argument is an easy one: J.R.R. Tolkien wrote The Hobbit as an adventure tale for children, so it's okay for it to have a lot of action scenes with a loose narrative structure. That may be true, but there's a bit more to the spiders than just being one more obstacle. There's a lot of fear surrounding Mirkwood in the story, enough to earn several warnings, and having the characters actually get captured by monsters inside that forest justifies that fear. Without the spiders, Mirkwood would just seem like a really dark place with deer, butterflies, grouchy elves, and rivers that you need to stay out of -- hazardous, but not menacing. Including the spiders also helps to drive home the story's lesson of listening to your elders; having the dwarves almost get eaten by monsters because they ignored Gandalf and wandered off the path leaves a much stronger impression than just having them get arrested by elves.
It can also be argued that the spiders serve to offset the elves. The Mirkwood elves are the beings that Bilbo's company gets the biggest warning about. They're the main obstacle in the forest, not the spiders. Prior to this though, the story presents elves more or less as allies, so they don't feel like much of a threat to the readers, the viewers, or the heroes. All of the trouble before Mirkwood comes from monsters, and having Bilbo fight off one more round of monsters in the forest only to have the elves capture his friends shows a transition in the story. Instead of vicious, evil creatures, Bilbo now has good but uncooperative people standing in his way. That means that instead of cutting and stabbing his way out of trouble, he has to harness his wits that he discovered during the Riddle Game with Gollum and be strategic from this point on.
Another thing to consider is that the fight with the spiders is the peak of Bilbo learning to embrace his adventurous side. He comes to the dwarves' rescue single-handedly for the first time, he names his sword and uses it for combat, and in the book, he makes up songs to taunt the spiders with as he fends them off. He's finally mastering the abilities that the quest has forced him to learn so far, and he's having fun doing it. The fact that he's going up against a nest of evil monsters with very little moral dilemmas about hurting them makes the scene fun for the readers and viewers as well. This creates an especially nice contrast with his refusal to fight in the Battle of the Five Armies after he grows wiser from his experiences.And that's the most important purpose of the spiders in The Hobbit. They show that the main character is capable of growing and changing. Bilbo's greatest internal conflict is that he wants to lead the quiet, predictable lifestyle of a hobbit despite being from a family that prefers the unexpected. He resists change in the first part of the story, and while it's helpful that he's good at fighting giant spiders in Mirkwood, it's more important that he decides to fight them at all. Thematically, the spiders are a test of whether or not Bilbo is adaptable and confident enough for the second half of his journey, and as soon as he passes that test, the Mirkwood elves step in to take things to the next level things for him.
