The weather has been so beautiful recently that sitting indoors to write blog posts is less appealing than wandering outside, with or without a camera.
Cairns Birdwing butterflies, Ornithoptera euphorion, are abundant here (because we grow their food plant) and always beautiful but we don’t often get a photo showing the upper wings of the males because they always (well, 99.99% of the time) shut their wings together while resting. Why? If they didn’t, they might as well be shouting, “Eat me!” to the birds. (Ulysses Swallowtails are the same, only more so. So are many other butterflies – bright in flight, camouflaged at rest.)
So here’s one I caught while he was hovering to feed, and again while resting.
Walking around the garden recently, I came across this mating pair of Cairns Birdwings, Ornithoptera euphorion.
They were hanging in the shade of a silver wattle which has Aristolochia, their caterpillars’ food plant, sprawling over it, so their location is unsurprising.
The fresh empty chrysalis nearby and the not-quite-developed wings of the female suggest that she had just emerged and the male had seized the opportunity to mate her before her wings were fully dry and she was ready to fly off. That also is unsurprising, since it happens often amongst butterflies; the females emerge as fully mature adults, so they are never too young in the way that (e.g.) mammals or reptiles might be too young.
We have been growing a particular vine, for years, just for the Birdwing butterflies whose caterpillars depend on it. Just what the vine is called and which butterflies depend on it are, however, recurring questions – for us as well as for the many other people who love the butterflies. This post pulls together information from botanical and entomological books and websites to try to settle both questions.
Very briefly, all species of butterflies in one group of Swallowtail butterflies have specialised to feed exclusively on one group of closely related plants. The butterflies are the Troidini, a “tribe” (in scientific language that’s a level between “family” and “genus”) of Swallowtails (Papilionidae) and the plants are the Birthworts (Aristolochiaceae).
Our Troidini are the Clearwing Swallowtail (Cressida cressida), Red-bodied Swallowtail (Atrophaneura polydorus) and all of the Birdwings (Ornithoptera species). The Aristolochiaceae we’re interested in are in the genus Aristolochia, or used to be, and many of them are known as Dutchman’s Pipe vines.
A friend sent me a photo of a caterpillar ten days ago, with two implied questions:
This caterpillar is feeding off native Dutchmans Pipe.
Also, the Cairns Birdwing caterpillars of several people I have spoken to have died and butterflies are scarce even though there is a plentiful food source.
The first question was easy to answer: it was a caterpillar of the Clearwing Swallowtail, aka Big Greasy, butterfly (Cressida cressida), which shares Aristolochia tagala with the Cairns Birdwing.
They are quite distinctive at every stage of their little lives. The tiniest ones are orange; a little later they are maroon with white spines; and finally they are creamy-white with some maroon markings, as in this old post.
When they are ready to pupate, Cairns Birdwing caterpillars drop off the Aristolochia vine they had been eating and climb a neighbouring plant. There they find an appropriate twig or leaf, reinforce it with some of their silk, make a sling with more silk, and hang there in their new hard brown skin (which is what the chrysalis is) while they miraculously re-organise inside it (see this blog post for more details). When the time comes …