Lucie - I want to make those spider nests, too. I know I'd use cheese cloth or cheap guaze fabric but I'm not sure if I would make it hard, like a paper mache method or soft sided. Have you given it thought?
Lucie/Kim - My SIL made one of these for her halloween party and formed it around a plastic skull...she let some of it show through as if the spiders hadn't finished yet and she hot glued some hair to the skull for added effect. it was truly gruesome!