Just what is a cobweb, really?

I looked it up in the dictionary, and Webster’s defined it as: a spider’s web, esp. when old and covered with dust.

Now there’s a visual for you. A spider’s web (as if that wasn’t bad enough), but one that is then covered with dust, and old. Is the spider equally as old and dusty? And again, another visual for you.
I’m not going to be able to sleep tonight.

Unkempt spiders.