Australia’s biggest butterfly is fooled by toxic plants
The Cairns birding (Ornithoptera euphorion), a member of the birdwing butterfly group, is endemic to pockets of coastal north-eastern Queensland. With a wingspan that can reach 20cm (in the females, which are larger than the males), they are the largest species of butterfly native to Australia, and among the largest butterflies on Earth.
They are closely related to the world’s largest butterfly, Queen Alexandra’s birdwing (Ornithoptera alexandrae) which is found in Popondetta in Papua New Guinea. The female’s wingspan, for comparison, can reach 27.5 cm.
Here’s a picture of a male and female Cairns birdwing, which shows off their difference in size and colouring:
Butterflies don’t tend to live very long (Cairns birdwings last about 4-5 weeks), and their lives revolve around fostering the next generation. The males are aggressive in their pursuit of a mate, which means the females are most often mated with as soon as they leave the cocoon (which honestly sounds pretty stressful).
Like many species, the Cairns birdwing has evolved to depend on certain features in their environment for survival and procreation. Two species of the evergreen vine genus Aristolochia provide the perfect surface for the females to lay their eggs on, and the perfect food source for their caterpillars.
Specifically, Cairns birdwings need to be nearby the Indian birthwort (Aristolochia tagala) and the Richmond birdwing butterfly vine (raristolochia praevenosa).
As the name of the latter plant suggests, the Richmond birdwing butterfly (Ornithoptera richmondia), which has a 16-cm wingspan in the females and is endemic to Queensland and the north-eastern corner of New South Wales, also needs this plant to thrive. The species looks very similar to the Cairns birdwing.
Female Cairns birdwings find these plants thanks to the chemical receptors in their forelegs, which they use to ‘taste’ the leaves. They also have sensory organs at the end of their abdomens, which can help them to identify the most tender leaves for the caterpillars to feed on.
Sadly, the pest varieties of the genus Aristolochia, the Dutchman’s pipe (Aristolochia elegans) and gaping Dutchman’s pipe (A. ringens), give off very similar chemical signals, but are actually highly toxic to the butterflies (and sheep).
All the more reason to make sure you don’t have any growing nearby, if you live in Cairns birdwing territory. The flowers are pretty hard to miss, they are bizarre and beautiful, but they have to go in order to help our giant butterflies thrive.