We know the identity of one of them.
The caterpillars seem to feed on the white-patch lichens but because of the concealment of the mouthparts, it is difficult to determine if they are feeding on anything else. It's obvious that the caterpillars incorporate some of the green material into their camouflage. Ants and other insects travel past the caterpillars and pay them no attention.
This year, the caterpillars were found on palm trunks and the trees where they were last year had no caterpillars on them at all.
I took two of the larger larvae and scraped a few bits of lichen off one of the trunks and placed it in a container. After a few days a cocoon was formed.
Enispa prolectus (Turner): Noctuidae; Acontiinae
The moth is relatively common and turns up regularly at the light sheet. Seven species of Enispa are known from Australia. It seems that little is known of their habits. Common (1990) records one species, E. plutonis (Lucas), living in spider's webs where they feed on the detritus such as dead leaves and the left-overs from the spider's catch. The caterpillar is naked and not covered with any detritus. Its pupa is suspended without any cocoon by its anal hooks. This is very different from E. prolectus. With E. prolectus, there is a cocoon that is suspended on a stem which is firmly attached to the substrate by silk.
The next step is to find the distinctive cocoons in the habitat. They most likely move to adjacent vegetation or, perhaps, under loose bark. This is in short supply on rainforest trees.
Thanks to Buck Richardson, and his moth identification site, for aid in identifying the moth.
Common, IFB. 1990. Moths of Australia. Melbourne University Press. Pp. 1-535.