Spiders are one of the quickest mobs. They can climb walls jump high and far, and they can go through 2 brick wide holes in your walls.

Ups: when they die, they give you string for bows, and spider eyes for who knows what.

Downs: they can spawn with skeletons on top of them which creates a spider jockey and they look really cool, but the skeleton shoots arrows and the spiders can still do all the normal stuff a spider can.

I would recommend shooting the spiders web sack(no the back of the spider for those dirty minded people.) If spiders got armor, that would be weird.