With an enormous wingspan of up to 28 centimetres, Queen Alexandra's birdwing is the world’s largest butterfly. Vibrantly coloured, this magnificent butterfly displays marked sexual dimorphism. The attractive male has blue-green iridescent streaks across the largely black wings, with a scattering of contrasting yellow spots. The larger female is somewhat duller, with a brown colour across the wings and yellow blotches on the tips. On both sexes, the head and thorax is black and the abdomen is a striking yellow. Like the adult, the caterpillar of Queen Alexandra's birdwing is conspicuously coloured, with a dark, wine-red body, numerous contrasting bright red spines and two large, yellow central spines. During metamorphosis, this butterfly forms a light brown, ground-coloured chrysalis.