So called because it can 'urt?
DF and I came across this 'Chinese Junk' or Cup Moth caterpillar today while we were orchid hunting around Moe - more of the orchid stuff shortly.
There are several different cup moth species that feed on eucalypts and they can vary in colour and size. The spines, (or urticating / irritating hairs), on the body can inflict a sting rather like a nettle.
There is some interesting information here that is worth reading, from the University of Sydney department of Medical Entomology regarding the effects of stings from these glorious looking creatures.