Where are our birdwing butterflies?

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.

However, I don’t know what’s going on with the Cairns Birdwing population. We’ve got quite a lot of the vine but we’re seeing hardly any of the butterflies recently and I don’t recall their caterpillars on our vines. I suspect a knock-on effect of last year’s floods. Perhaps fewer caterpillars made it to maturity last year than normal, so numbers of the current generation are down? Perhaps the non-native Dutchman’s Pipe survived the floods better than the native one and poisoned many of last year’s caterpillars?

I spent some time checking our vines today and found quite a few Clearwing eggs –

Egg of Clearwing Swallowtail, Cressida cressida

– and caterpillars –

Very young Clearwing Swallowtail caterpillar, just growing out of its orange colour scheme

– and saw both sexes of the adults in courtship flight, and the female on the vine –

Male Clearwing Swallowtail in flight
Female Clearwing Swallowtail in flight near Aristolochia

– but no Birdwing eggs or caterpillars at all. I hope to see their numbers recover in due course.

5 thoughts on “Where are our birdwing butterflies?”

  1. The balance between the species has been improving steadily since mid April and we now have quite a lot of Birdwing caterpillars, some of them almost ready to pupate, as well as the Clearwings. We’re still not seeing many adult Birdwings, however.

  2. Hello Malcolm,
    Thanks for your blog, …
    In our street in Aitkenvale we are all obsessed with the Cairns birdwing butterflies and have had many reach maturity over the last few years. 
    I have a question about the clearwing caterpillars that I haven’t been able to find an answer to on Google so maybe you can help. 
    I have a couple of large birdwing caterpillars at the moment but I just found a very small caterpillar that I was not sure if it was a birdwing as it was black and white rather than orange spikes but it has the little orange ‘horns’ that it sticks out when disturbed.  Do you know if the clearwing caterpillars also do that?  
    Thanks,
    Cathy

    1. Hi, Cathy,
      It’s great to hear of more of my neighbours sharing my liking for Birdwings!

      I’m pretty sure the caterpillar you found was a Clearwing Swallowtail. They do change colour as they mature but they are basically dark maroon and creamy-white. Here’s a young one – https://www.flickr.com/photos/malcolm_nq/10549465125/

      And yes, they do have those little orange horns. I thought they did but wasn’t absolutely sure so I just looked them up, and it turns out that all swallowtail caterpillars have them. This wikipedia page confirms it for the Clearwing, too. It also told me that they are not particularly closely related to our other swallowtails, but instead seems to be the closest living relative of some South American swallowtails. The name for the horns is “osmetrium” and if you search on that term you will find out more.
      Thanks for your question!
      Malcolm

      1. Hi Malcolm,
        Thanks for all the info.  
        There’s plenty room on the vine for all the caterpillars to share :-) 
        You’re right though, there have been far fewer butterflies around laying eggs this year, and last year too compared to the previous few years when we had so many caterpillars the vines weren’t big enough to cope. 
        Cheers,
        Cathy

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