I've lately seen a lot of instances where a leaf is dangling from a piece of web coming down off a tree. What purpose/s does this serve for the spider? Is it some sort of mechanism for the spider to determine the wind / disturbances in that region?
I've seen a suggestion that it's to help act as a plumb during web construction to keep part of it tight, but do we actually know for sure?
Here's a national geographic image showing what I mean: http://ngm.nationalgeographic.com/ngm/photo-contest/2012/entries/177963/view/