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 few weeks ago I received an enquiry from a reader: did I know what was happening with the Blue Tigers at Horseshoe Bay on Magnetic Island?
At that time all I knew was second-hand or worse but soon afterwards I saw a local ABC News report about thousands of them on the site of the old Horseshoe Bay school, which I was fortunate enough to visit with family and friends at the end of May. It was a magical experience.
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.
Rain makes the plants grow and provides ideal conditions for caterpillars and other vegetarian insects so we’re now in peak butterfly season.
One very slow walk around my garden was enough for me to take the photos you see below. I missed the Common Crow (old pic here), which we see often, and the Orchard Swallowtail and Cairns Birdwing, which are fairly regular visitors, but otherwise it’s a good overview of the larger species we see at this time of year.