Well, deadly for small insects, anyway.
A few days ago, a gigantic spider took up residence on our front porch, stretching her wide web across the open air between posts. During the day, she lounges on a dead leaf, one foot touching the web (perhaps so she can feel the vibrations in case something lands in it):
At night, she takes up her position in the very center of her web:
When I say she's "gigantic", I mean that I have to do a double-take whenever I catch a glimpse of her out of the corner of my eye. Her body alone is about 3/4 of an inch long, and the distance from the tip of one toe to another is an inch and a half. I suspect her species may be Neoscona crucifera, but I don't know for sure -- and I'm fairly certain she's female just because of her large size.
I admit, I put a cricket in her web last night, and it was almost frightening how quickly she was on the smaller creature, rolling it up in an instant and sinking her fangs into its body.
From what I've seen watching this girl, Shelob and Aragog might not really be so far away....