Last year our maple got covered in aphids, and it seems they are returning again this year. Fortunately, the ladybirds have made a comeback too, I can't wait to spy their larvae all over the tree. We can currently see ladybirds mating and their little yellow eggs on the tree trunk. There are over 100 species of ladybirds in Australia, I think we may have at least 3 varieties, all of which are very fond of our aphids.
I am a fan of most caterpillars, but spitfires really gross me out. A great link about them and the sawflies they will become here. Sawflies are nowhere near as hideous as their oozing spitting larvae.