The Saunders' Case Moth is a large Psychid 'bagworm' which consumes a wide range of plants. We usually see them on Eucalyptus, Acacia trees but this one was on a very strong, hollow stemmed, water grass.... so it's a case of - 'whatever'.
On lakeside 'reeds' in wetlands reserve.
Room for some doubt on ID - must check possible reed-based life cycle. Distribution http://bie.ala.org.au/species/Metura+elo...