Cairns Birdwing butterfly pupation and emergence

caterpillar hanging from leaf
Beginning pupation. Note how the leaf and stem have been reinforced with black silk.

I have been writing about Cairns Birdwing butterflies quite often but there are still more things to say (and our visitors always seem delighted and fascinated by them) so I will keep adding to the story.

Pupation, the process of forming the chrysalis, changing inside it and emerging as an adult, is one of the most  baffling processes in nature. I’m not even going to speculate about how an insect could have evolved such a bizarre practice but want to share my observations of the beginning and end of it.

Birdwing caterpillars eat until they are big enough and then leave the vine they have been feeding on and attach themselves to a nearby plant, often a metre or two off the ground (sometimes they drop from the vine to the ground to crawl up the stem of another plant). The one in my first photo chose the twig of a rose bush and I was intrigued to see that it reinforced the rose with strands of silk running down from the branch, over the leaf and around the twig – a sensible precaution against the leaf falling off, of course, but again one has to wonder how it evolved (as usual, click the photo to see it better). It then made a silk sling from the plant around what would be its shoulders if it had shoulders, and hung tail down for a surprisingly long period – a couple of days.

But how do they get into their chrysalis? I have to admit to relying on vague memories of silkworms, but those memories put me on the wrong track entirely because they don’t “get into” the chrysalis at all. Rather, they form it under their skin, then shed the skin just as they have already done several times during their growth as a caterpillar.

birdwing butterfly chrysalis
A very new chrysalis, with the discarded skin still dangling from it.

I actually woke up to that – and to my own ignorance – when I saw a fresh chrysalis, not yet hardened, flexing to shrug off the last part of its skin. In this second photo (not the same caterpillar, of course) you can see the crumpled skin, complete with head-shell and legs, still barely attached to the chrysalis.

A related point is the difference between a chrysalis and a cocoon. As Museum Victoria point out here,  “the skin that emerges from under the old skin is a chrysalis. Both butterflies and moths develop a chrysalis in their pupal stage, but the chrysalises of moths are usually contained inside a woven structure made of silk – a cocoon.” Silkworms are the caterpillars of moths so they form cocoons around their chrysalises in just this way – see Wikipedia for more information.

The really mysterious stuff happens in the chrysalis, over the next month or so in the case of our Birdwings, and then the chrysalis splits and a damp butterfly emerges with crumpled wings. As soon as they straighten and harden, she – or he, as seen below – is off and away in search of nectar or a mate.

green and black butterfly
A male Cairns Birdwing on the chrysalis he has just emerged from
green and black butterfly flapping its wings
His first tentative wing-strokes. He flew off a few moments later

Cairns Birdwing butterflies emerging

black and green butterfllies
A female Cairns Birdwing (top) has just emerged from the chrysalis at lower right, and the older male has mated her immediately

Three weeks ago I wrote about the collection of Cairns Birdwing chrysalises we found on our bottlebrush tree and observed that we should be seeing the adults emerging “around the end of the month.” They have been appearing for a few days now, so it seems that some of the chrysalises were a bit older than we thought.

black and green butterflies
The same mating pair, fluttering up the tree

Normal courtship involves the hopeful male flying close below and behind the larger, darker female as seen here and doing aerobatic tricks around her; if she is impressed enough, she will allow mating to begin.

However, males have no compunction whatever about taking advantage of a female who is still waiting for her wings to stretch and dry after squeezing out of her chrysalis, and that is what has happened in the photo above.

(How do I know the male is older? Simple: when you look closely, you will see that his wings are quite battered.)

As her strength increased, she fluttered and crawled higher in the foliage, dragging him with her.

black and green butterflies
The same couple at a better resting point

This happened late yesterday afternoon and was the second emergence we saw during the day. Meanwhile, we still have half-grown caterpillars in the garden, and others full-grown and beginning pupation.

I checked on the seasonality of the species and Braby’s huge, authoritative Butterflies of Australia said that adults appear all year round but chrysalises can lie dormant for some months in the dry season. That makes sense, since there is no point emerging as an adult when the caterpillars’ food plants are not growing well.

Don Herbison-Evans’ page about the species lists their food plants and provides links to information about them.

black caterpillars
Caterpillars eating the bark of an Aristolochia vine on the trunk of a bottlebrush tree

Our caterpillars have been eating the bark of the main stems of our largest surviving vine and (once again) we would love to hear from people who have more Aristolochia. I’m sure that if we gave away all the caterpillars we could find we would still have more than we can feed.

The Clearwing Swallowtail butterfly

clear-winged butterfly near creeper
Clearwing Swallowtail in flight near Aristolochia vine

Clearwing Swallowtails, Cressida cressida, lay their eggs on five different species of Aristolochia, according to Don Herbison-Evans and Stella Crossley’s great Butterflies of Australia site. Peter Valentine (Butterflies of the Townsville Area) agrees, adding that they especially patronise “the low small species scattered through the grasslands.”

The caterpillars change colour and pattern as they grow. The three below are all Clearwing caterpillars, at early, middle and late stages of development.

Caterpillar of Clearwing Swallowtail 9389

Caterpillar of Clearwing Swallowtail 7227

Caterpillar of Clearwing Swallowtail 7223

Cairns Birdwing caterpillars (Troides euphorion) also depend on Aristolochia – four native species of it, in fact. However, there is only one species that both kinds of caterpillars like: Aristolochia tagala

Here for comparison are Birdwing caterpillars, showing young and old since they also change considerably as they grow:

Caterpillar of Cairns Birdwing 7217

Birdwing caterpillar 9466

Recently we have had both species of butterfly laying eggs on our vines and we can’t grow enough of them to feed all the caterpillars that hatch. It’s a continuation, really, of the situation we had back in May. Part of the problem is that a single caterpillar can consume a whole vine seedling within a day so we have difficulty rearing a vine past its infancy; we may have to begin growing them under wire mesh until they are well established.

Wasp and caterpillar

Wasp on tip of hibiscus leaf
Wasp in hunting mode

When I saw this wasp (Vespidae, Eumeninae) looking so busy on the tip of an hibiscus leaf I naturally looked more closely and saw what she was after, the very slim yellowish caterpillar in its retreat.

The action didn’t last long. The wasp flew off and the caterpillar was no more to be seen; I assumed that the wasp got her prey but it’s possible that the caterpillar escaped by dropping from the leaf on a thread of the silk it used to construct its retreat.

The caterpillar's retreat: the sides of the leaf are pulled together with silk, and there is a caterpillar-sized hole at the upper end
The caterpillar’s retreat: the sides of the leaf are pulled together with silk, and there is a caterpillar-sized hole at the upper end

I had seen these constructions before but never known what made them or why, so the incident solved a mystery for me.

The wasp, by the way, wasn’t hunting on her own account but for her progeny. All adult Vespidae (which covers most of the insects most of us think of as wasps – see this page on the Brisbane Insects site) feed on nectar but hunt caterpillars or spiders for their larvae. Paper wasps are included in the family – see this post about their life cycle for a photo of one with a ball of minced caterpillar – and here for good measure is a shot of our large black-and-yellow mud dauber with a caterpillar.

If it matters, these photos were taken nearly three months ago, in mid March, but I didn’t find time to upload them before my holidays. Better late than never, as they say.

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?