I love spiders and hate the slander they constantly go through in our society. That said, a spider infestation almost certainly means the spiders are sustaining themselves on each other. I don't know a single species of spider that doesn't cannibalize.

There are exceptions, of course. Perhaps most notably, a super colony(yes colony) of multiple species of cave spiders that subsist off of some tiny mass-producing bug. I forget the specifics.

Yep. Spiders are free pest control to me.