Can you take it into protective custody, rear it to get a moth, then take the moth back and release it where it came from (taking a photo of the moth first)?
Don - I am sorry, We could not find the caterpillar again, even though the sapling is very small. Apologies also because, after comparing leaves with other nearby trees, I now know that it is a Cherry Ballart, not a casuarina, so I have edited this entry. I carefully checked a couple of larger Cherry Ballarts about thirty metres away for similar caterpillars (and also Tower Casemoths), but did not see any. Apologies, Jacky