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

11 thoughts on “Cairns Birdwing butterfly pupation and emergence”

  1. Wow, thanks, I didn’t know that, about the chrysalis forming under the skin. But, how are the silk slings connected to the caterpillar so they aren’t lost when the outer skin is shed? What a fascinating process to watch!

    1. I’m not sure that the sling is glued to the caterpillar’s skin. One of our emerging butterflies left its chrysalis hanging from the sling but they weren’t stuck together – I lifted the chrysalis away with one finger to leave the loop dangling freely from the leaf.

  2. we managed to catch one of our caterpillars making its sling on video, it forms the loop and then slips its body through the loop, then adds some final touches from inside. it has been fascinating to watch. I also managed to video tape 2 of them shedding their skin, however the second one has struggled to shed the whole skin and is stuck with part of its head still on. I am wondering if it will gradually get out of it or if it will die because of this.

  3. I found a caterpillar on a young vine given to me. The vine hadn’t yet produced any ‘flower’ and when it had climbed about 5 feet in length the caterpillar appeared. I’m not sure how long it’s been chewing now but all of the top leaves have been eaten and there are perhaps only about ten left at the bottom of the plant. I don’t want the caterpillar to starve ! What should I do? Buy another plant and move the caterpillar to it? And…can I handle the caterpillar? How would I move it?

    1. It’s a perennial problem, Chloe, as you will see from other comments. The way to give you caterpillar the best chance is probably to find a well-established vine in a friend’s garden and carry it across. If you buy another small vine, you may have the same problem again in a few weeks.
      They don’t like being handled but cope okay so long as you’re gentle and patient.

  4. My sister has been cultivating pipe vines for several years just north of Townsville. There is rarely any leaves or remnants left after a caterpillar attack. She has found smaller chrysalis afterward and has presumed that the butterflies might be smaller if vines are scarce. She has had lots of bird wings in here garden. When she put the first vine in the leaves were gone in days. The more vines she has, the more caterpillars are there. Worthwhile endeavour.

  5. I note it was advised to leave the chrysalis on plant but have lost several having found a hole drilled into them, made the decision to remove them with twig attached and bring them inside to hatch, I peg them around the rim of a container standing in water to eliminate ants. This has worked very well.

    1. Thanks, Norma. That extra level of care may well pay off. I have a friend who moves pupae into a miniature mosquito-netted gazebo in a corner of her garden and she thinks it improves the survival rate. The downside of moving them is that you need to ensure temperature, humidity and light levels are not too different from their original location, and that the emerging adults can soon fly freely to food sources.

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