I do not know any moth species that just attach an ellipsoidal cocoon with no camouflage vertically on a trunk like that. It is so conspicuous. But there many cocoons I do not know. Its form suggests Bombycoidea. I think it is too large for local Lasiocampidae, Eupterotidae, or Saturniidae; and Sphingidae usually pupate under the soil. For Anthelidae, I think it is too large for an Anthela species. The next largest to C. collesi is C. chalepteryx, but that caterpillar feeds on Acacia species, so its cocoon would be unlikely to be on a Gum trunk. Quite a puzzle.
C. collesi do spin cocoons in open sight (although usually under some sort of overhang), apparentlyre relying on the tough spined cocoon rather than disguise.