source: wiki commons
Because they are small, spiders have many enemies.
Larger animals, such as birds, toads, lizards and monkeys, hunt them. But they are also used as food by many smaller creatures. Ticks will attach themselves to a spider and eat away at it for a long time while the spider goes about its business.
One of the spider’s worst enemies is the Spider-Wasp. The female wasp will paralyze the spider by stinging it. She then digs a hole and puts the spider and an egg into it. When the egg hatches, the baby wasp will eat away at the paralyzed spider.
We (humans) are also enemies of spiders. Besides stepping on them, the pesticides we use to control other insects can kill spiders.