Like a spider in your basement. Spiders sneak in through the tiniest holes, which you often don't even know you have. Spiders get in no matter how hard you try to keep them out. Indeed, spiders are just about everywhere. Spiders run away when you try to catch them, but they don't actually leave.
Many people are unnecessarily afraid of spiders.
Some people, however, tolerate spiders as long as they don't get in the way. They're annoying, but most spiders don't harm anything. Spiders don't like to be exposed. Some spiders are poisonous, but most aren't. Indeed, many Spiders collect and feed off bugs.