Now That’s a Caterpillar. Wallace’s Golden Birdwing butterfly

At a butterfly farm on Bacan in the Moluccas, Wallace’s Golden Birdwing butterflies (Ornithoptera croesus) were being bred. A very large cage mesh cage was planted with food plants and contained the birdwing at all stages of development. Adults were flying in the top of the cage but there were also males outside trying to get in.

The caterpillar is particularly spectacular giving every warning to potential predators: do not eat me; I will poison you*; I have nasty spikes; do not even think about it.

Chrysalis

A bereft of life with colours fading adult male--dorsal view

Ventral view

The caterpillar is spectacular but it was the adult butterfly that Alfred Russel Wallace became so excited about when he first found them. His letter from Bacan, dated 28 January 1859 was read at a meeting of the Entomological Society of London on 6 June 1859:

…You may perhaps imagine my excitement when, after seeing it only two or three times in three months, I at length took a male Ornithoptera. When I took it out of my net, and opened its gorgeous wings, I was nearer fainting with delight and excitement than I have ever been in my life; my heart beat violently, and the blood rushed to my head, leaving a headache for the rest of the day. The insect surpassed my expectations, being, though allied to Priamus, perfectly new, distinct, and of a most gorgeous and unique colour; it is a fiery golden orange, changing, when viewed obliquely, to opaline-yellow and green…

…It is, I think, the finest of the Ornithoptera, and consequently the finest butterfly in the world?

…For the Ornithoptera I propose Croesus as a good name.

Croesus is a highly fitting specific name for the species; the old gold made it as rich as Croesus and to Wallace it was pure gold twice over, ‘the finest butterfly in the world’ and the collectors of butterflies back in Britain would be willing to pay a great of money to add a specimen to their collections. That is, after all, how Wallace made his living.

The species is sexually dimorphic, the female looks entirely different as this plate from a book by Robert Henry Fernando Rippon (ca 1836-1917):

Wallace's Golden Birdwing is found only in the northern Moluccas to the east of Wallace's line. There are differences in coloration on the different islands and they are regarded as subspecies. That on Bacan is Ornithoptera croesus sananaensis.

Distribution of Wallace's Golden Birdwing

This video on YouTube of Wallace’s Golden Birdwing in the wild is worth watching:

We remarked while in the Moluccas how uncommon butterflies appeared to be. We had seen lots on just a short walk on New Guinea itself a few days earlier. But it wasn’t just us. The great man himself in his letter from Bacan to the entomologists in London wrote:

Butterflies are scarce…

At the butterfly farm. The large cage can be seen in the right of the photograph.

*That’s assuming the caterpillar is poisonous. It could though be a Batesian mimic—‘I do not need to make expensive toxins if I just copy the colours of the other caterpillar over there who does’.