The caterpillars can get very sizeable and can be slightly different in colouration.
These guys, like most caterpillars, are voracious eaters and a small group can defoliate an entire vine. I have read that if all their food has gone, then the caterpillars may resort to cannibalism. Yikes....! I suppose the big eat the smaller?
Fleshy spine-like tubercles line the caterpillars' backs, and they have a pale "saddle" marking that can be challenge to photograph.
Like other members of their family, birdwing caterpillars possess a retractable organ behind their heads called an osmeterium. Shaped like the forked tongue of a snake, the osmeterium excretes a fetid terpene-based compound and is deployed when the caterpillar is provoked.
The caterpillars are also unappealing to most predators due to their toxicity: the vines which the caterpillars feed upon contain aristolochic acid, a poisonous compound known to be carcinogenic in rats. The feeding caterpillars incorporate and concentrate the aristolochic acid into their tissues, where the poison will persist through metamorphosis and into adulthood.