This spider has a bottom that looks like the head of a Hawk Moth - I wonder if that is its purpose and why? see http://www.bushpea.com/in/pg/all/c/coprosma%20hawk%20moth%2005.html
Thank you Michael, certainly seems a plausible explanation. I actually had idea there was so many Orb spiders and they are hard to ID, thanks to CNM I am leaning so much!