[update Nov-2015] Finally worked out that these are Gum Tree Shield Bugs
These bugs were on a tree in the wildflower gardens. I’ve been trying to work out what they are. What bug is that looks comprehensive and has a good bug identification tool but I’ve been unsuccessful so far.
They’re quite distinctive looking, part of my problem is describing it in a way that someone who knows this bug would write about it. I found out entomology is very specialized and has a whole language of it’s own!