I looked out my bedroom window today and realized I have bag worms in my river birch tree. I can see 2 areas. They are very high up and I don't see how I can do anything about them without paying a lot of money to someone who can get as high as the upper part of a second story house. So I was just going to ignore them. How much damage will they do to my tree?
I also have a river birch. I frequently get fall webworms in my tree, which is what I suspect you have. They are often called bagworms by mistake. Here are 2 links for your reference.
Fall webworms: http://extension.umd.edu/hgic/fall-webworm-trees
Mostly, fall webworms are a nuisance pest since they are unsightly. They eat the foliage inside the web but that foliage has already done most of the work of making food for the tree this season. The health of the tree is not in jeopardy. Yes, if you could reach the branches it would be good to prune out the webs and dispose of them in the trash. But it is not worth the expense of calling in a professional.