Birdwing butterflies again

I posted a photo of a male Cairns Birdwing a couple of weeks ago with the comment that they are so common that “I rarely bother pointing a camera at them.” As usually happens in such cases, I proved myself wrong soon afterwards.

The occasion was my sighting of a female which I thought might be of the Northern species, the New Guinea Birdwing (Ornithoptera priamus), which shouldn’t be seen in Townsville according to the books. I then wanted to check that the local males weren’t (also?) New Guinea Birdwings but that meant getting a good look at the upper surface of the wings, which is not at all easy.

Birdwings and Ulysses on any rack of tourist-trap postcards lie around with their wings gaudily spread but in real life they do nothing of the sort. The wings slam shut as soon as they perch, presenting their much more discreet undersides to the gaze of predatory birds. Almost the only way of getting a photo of the upper sides from a wild swallowtail is to take a burst of shots of a hovering butterfly and throw away most of them. That’s how I got this one.

Cairns Birdwing
Male Birdwing butterfly

There are a few points of interest:

  • Getting a really sharp, clear photo by this technique is a fluky business. You need lots of light so the shutter speed can stay high enough to freeze the movement (I didn’t have that luxury), and enough shots that at least one of them is well composed.
  • It is definitely a Cairns Birdwing, not the northerner, because the large central black area has no green streak through it. That’s a little disappointing but not surprising.
  • The wings are catching the light at very different angles and show the same kind of apparent colour-change as the Eggfly. In this case, the bright yellow-green of the wing becomes bluish-purple when seen at an acute angle; it can look even more purple in flight, depending on the angle of the sun.
  • And this is an old, battered individual. The trailing edge of the left fore-wing is ragged, and the coloured areas have scratches where scales have been scraped off. This sort of damage is why I noted that the Lurcher (click here and scroll down) was rather elderly.

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.

Cairns Birdwing chrysalis

brown pupa in tree
Cairns Birdwing chrysalis

We’ve had lots of Cairns Birdwing (Troides euphorion) butterflies in our garden in the last few weeks. Every time we go outdoors we are likely to see an enormous black and yellow female or one or two of the vivid green and black, only slightly smaller, males (photos here).

And we are re-running our caterpillar-feeding problem, since our Aristolochia vines haven’t recovered from the last feeding frenzy. We have been moving the caterpillars where we can but today I saw a well-grown individual resting quietly on a rambling rose that it had nibbled for want of anything better, and I couldn’t see any more Aristolochia to move it to. I suspect its outlook there is poor but on the other hand it may be ready to pupate.

They don’t pupate on the vine but on nearby vegetation. The one above is in a bottlebrush tree which supports a vine, so it may have crawled down and or it may have made its way across from elsewhere. In any event, it is hanging just above knee height and it’s doing fine so far.

Update 5.4.14

This is kind of embarrassing but in a good way: sustained examination of the bottlebrush and the rose next to it reveals that we have about ten birdwing chrysalises, not just one or two. The lethargic caterpillar on the rose leaf has begun to pupate by making itself a silken sling like the one you can see above. (That is all it has done today, which seems like very slow progress.) We still also have large, active caterpillars – at least two on the vine in the bottlebrush.

The duration of pupation has been recorded as 26 days, according to Braby’s authoritative Butterflies of Australia, so we should be seeing them emerge around the end of this month.

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.

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?

Growing old gracefully

Battered Cairns Birdwing butterfly
An elderly female Cairns Birdwing butterfly, Ornithoptera priamus euphorion, on hibiscus leaves

We usually think of butterflies as fresh, bright, beautiful and short-lived (which I guess is why they are never ‘old’ in our minds) but that is not entirely true. Most of them certainly live for more than a day or two and many of them live for months. Wikipedia tells us that some species live for nearly a year and migrate surprisingly long distances – up to 5000 km. It makes sense, then, that we can see signs of ageing in our lepidopterous visitors.

The lady in my photo above turned up in our garden last week and shows plentiful signs of small accidental collisions and injuries. The edges of her wings are tattered, and she has lost many of the coloured scales from her wings. She is still impressive, however, with her 150mm wingspan and strong flight.

Cairns Birdwings lay eggs in our garden and they hatch, grow into large caterpillars, pupate and (sometimes) emerge as fresh, bright and beautiful adults. But a lot of our adults arrive from points unknown in quite battered condition. Braby’s monumental Butterflies of Australia says that some Australian swallowtails are migratory but suggests that movements of many others are dictated by seasonal changes in food supplies and can’t tell us whether or not our Birdwings are migratory. My guess, for what it’s worth, is that they could be loosely following the monsoon from North to South and back again as our Wet season develops and retreats. If so, our old lady above may be a Cairns Birdwing by birth as well as by name.