Via Wired:

Cornell University arachnologist Linda Rayor and Aviles also agree that what’s probably being filmed is a massive P. bistriata colony. That species lives in South American savannas and spins colonial webs. A bit of good news is that their venom is not believed to be harmful to humans, Uetz said.

Basically, they're hunting, and they do this in large-ass groups on a regular basis. I'm pretty sure that's why I've been having the same dream for the last 467 nights in a row. Only in my dream, these plump little gobbets of terror are coming down from my bedroom ceiling and then crawling under my covers and then under my skin. And then I realize I'm actually awake and on a public transit bus. Is that normal?

Sorry, Dominic.