Lepidoptera Butterfly House records that : ' The caterpillar (C. synopla) has been found feeding on : Elephant Ears ( Alocasias pecies, ARACEAE', but I expect that's native to the tropics. You can see some of the other species that moths in the Cruria (genus) have been recorded feeding on by going to that website.
Yes I saw the Alocasia report in Ian Common's book but this appears to refer to C. donowani that appears to be the common local species as reported on CNM. Its larvae also feed on Hibbertia, Cissus and Boerhavia. Alocasia or Cunjevoi grows in rainforest down as far as Sydney but is widely planted in Gardens further south and occurs in the ANBG on the edge of the rainforest gully. The larvae shown here were seen near Shepherd Rock and appear to be the first record on CNM of this species locally and may have fed on something like Hibbertia that is quite unrelated to Alocasia.
I am worried about the brown head. The larva of C. synopla has been recorded as having a black head. Ian: can you tell if there are Agaristines found in the ACT that do not have a larval photo in http://lepidoptera.butterflyhouse.com.au/agar/agar-cats.html ?
Looking at ALA all the records in NSW bar one come from the coast where its potential food plant Alocasia occurs. The one inland record of an adult comes through i-naturalist and is from ANBG by rod&deb in 2021 and identified by yourselves. Its alleged food plant is here.
I am looking at this picture from an ecological angle and it does not seem to fit what we know of synopla. According to ALA and Common there are 7 species in the genus.
Owen, it does look like sawfly larvae, but I do not know enough to be certain, and I have added another sighting from this morning when I returned to see if I could re-find them. See 4431258. They do look similar to some moth larvae, but I do not know if moth larvae associate together like this?
I think you are right Don. This photo http://lepidoptera.butterflyhouse.com.au/none/sawfly5.jpg from this page http://lepidoptera.butterflyhouse.com.au/none/sawfly.html on your website is virtually identical.