The Cairns Birdwing caterpillar is a large, dark brown to grey larva covered in long, fleshy orange-red spines that warn predators it is poisonous. It also has a forked, fleshy organ called an osmeterium behind its head, which it everts to release a strong-smelling chemical when threatened; it feeds exclusively on native pipe vines, storing their toxins for protection, and can grow to about 9 cm long before pupating..