I collected a few of these galls yesterday, while walking along the Ottawa River. I could tell that they were empty because there was a hole in the gall(seen on the left side of the upper half of the gall). I split it open to find an empty moth cocoon (the brown case) and wrapped around it, a fine silk web, which may or may not be from a spider. Will have to see what I can find out about this. These galls are elongate swellings on the goldenrod stem, unlike the very noticeable round swellings of the goldenrod gall fly http://www.pbase.com/laroseforest/image/130201116).