Apparently, sawdust was once a popular insulation material. Our ceilings are packed with it and a brief inspection today supports that it's in the ground floor as well. I've seen a number of discussion board comments about rodent/insect problems and sawdust insulation, but we've found no evidence of infestation this far. (We did find two pieces of bone today, but both were too big to be a rodent - not that this is necessarily comforting). It is dry and very light. We've been shoveling it into large garbage bags to remove it.