This is a late instar caterpillar now. I found this one, and one other, when they were recently hatched from their eggs, several weeks ago. Now this individual has changed completely from the black and yellow striped caterpillar to this beauty! Soon time to pupate I think. This species is a member of the Giant Silkworm Moths, most of which have those brightly coloured 'knobs', which are not poisonous despite the colour, and are quite harmless.