Several nests of larvae in a few Elderberry Panax (see sighting 4410800), probably different instars. And no, we did not take any into protective custody. Found by @SuziBond
Although the photo of C. australana larvae on P, sambucifolius on page 120 of 'Moths in the ACT' is difficult to match to this photo, yes, I do think this photograph of a larva looks very similar to this record on the ALA of a larva of C. australana recorded on Elderberry Panax: https://biocache.ala.org.au/occurrences/2a37fcb8-c3b7-4b81-ab75-549b7ca83568 .
Christine, thank you for this suggestion,. You are likely to be correct that your photo is of C. australana, but I agree with donhe that we cannot be sure in this case. More information may be able to verify your suggestion in the future. I support any attempt to understand the ecology of these moth species because so little is known.