You've seen the fall webworm 'nests' in many of the trees in the riparian area above the dam (and elsewhere). On 11/17/10 we saw several of these little guys out on a limb. Not more than an inch long, heading out to pupate, they will turn into - you guessed it - fall webworms (moths). Take a look here for a photo.
Saw several of these on 11/17/10 as well. This is (already) a butterfly, though, not a moth. What's the difference, you ask? I say: "To the internet!" More info than you need to become an expert. Thanks again to Ned Harris for the expert photos.