Butterfly vines and Swallowtail butterflies

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.

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Caterpillar rescue

The Cairns Birdwing, Ornithoptera priamus euphorion (formerly Troides euphorion), is our biggest and one of our most spectacular butterflies (female, male) and it is one of the few that we actively encourage in our garden. The adults only need nectar and they aren’t very fussy about which flowers they feed on, but their caterpillars only eat one plant, the Aristolochia vine, so our encouragement takes the form of planting the vine.

From five weeks ago until last week we had a semi-resident female attended by a couple of males, and she was laying eggs as though she was going to repopulate the whole suburb, if not the whole city. That’s great, we thought, as she flitted from one creeper to another … and then they all started hatching.

spiky black caterpillar
Just hatched: the young caterpillars, about 5 – 10 mm long, have branching spines

And eating.

spiny caterpillar
Halfway to maturity: about 25mm long, and the spines are now smooth but more colourful

We don’t mind the caterpillars eating the creeper – that’s what it’s there for – but their appetites are enormous because they have to grow to the size of my middle finger before they are ready to pupate, and before long we could see that they were in trouble: our vines were not big enough to feed them all and they were likely to starve before they matured.

What to do? We moved a couple of caterpillars to a young vine that their mum hadn’t noticed … but then watched in dismay as a bigger vine wilted and died; picked caterpillars  off the dying leaves and moved them to another vine; watched that vine shrink by the hour under a double load of ever-larger munchers; asked neighbours if they had vines (no luck); gave some caterpillars to a friendly school-child whose (enlightened) school had vines; gave some more to a friend whose friends had vines; and hoped that the remaining leaves would last our remaining caterpillars until they pupated.

So far, so good: one pupa that we know of (there may be one or two more) hanging on the one surviving vine, two more caterpillars which are so big they must be ready to follow suit, and still half a dozen leaves for them to eat. Phew!

But if their mum comes back, we will have to lock her away from her boyfriends. Enough is enough, okay?

Cairns Birdwing, laying eggs

A tangled mess of creepers sprawls untidily near our front gate, supported by the tall stump of a grevillea and a couple of nearly-dead frangipanis. It is really not very attractive but we leave it alone for the Aristolochia vine which threads through the Golden Orchids, Gloriosa and other creepers.

What’s so important about Aristolochia? Simply that the caterpillars of the spectacular Cairns Birdwing, Ornithoptera priamus euphorion, will eat nothing else, so a vine guarantees frequent visits from Australia’s largest butterfly. A couple of days ago I saw the first female of the season laying her eggs on it:

Cairns Birdwing butterfly, Ornithoptera priamus euphorion, laying an egg on Aristolochia vine
Cairns Birdwing butterfly laying an egg on Aristolochia vine. (Its leaves are seen most clearly on the left of the photo.)

These very large butterflies hover to feed and they hover – very briefly – to lay eggs too: one dab under a leaf and off she will go again. She will repeat the process dozens of times in a single session, then fly off to rest, feed and perhaps mate again.

The eggs hatch into dark spiny caterpillars which turn greyish as they grow to finger-size, then pupate in leaf-like cocoons before emerging, months later, as adults. Clicking here will take you to a collection of my older photos showing males, females, caterpillars and cocoons.

A word of warning from the Wet Tropics Management Authority: Growing the native rainforest vine Dutchman’s Pipe (Aristolochia tagala) will encourage regular visits by this impressive butterfly. However, beware of the exotic Dutchman’s Pipe (Aristolochia elegans) which is poisonous to the Cairns Birdwing caterpillars.