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 –
– and caterpillars –
– and saw both sexes of the adults in courtship flight, and the female on the vine –
– but no Birdwing eggs or caterpillars at all. I hope to see their numbers recover in due course.