When I browsed through some of the photos I took last week at Homerton I noticed that this little fellow suddenly acquired antennae - in a series of about ten photos the first five have no antennae and the last five there they are clear as day. What was going on? So I did a bit of reading.
It's a Paropsine Leaf Beetle Paropsis sp., one of the Chrysomelidae family, relatively common leaf-eating beetles. They feed on Mytaceae species, mostly eucalypts.
One of the characteristics of the Paropsids is that they can withdraw their legs and antennae from predators while sitting on a leaf. That's what I had inadvertently captured in the photo sequence. You can just see the tip of an antennae in the first photo.
Another characteristic is that they are extremely poisonous if eaten but I don't suppose I'll ever eat one so I'm not very worried.