Fuscus Swallowtail Caterpillar from Australia

Subject: Caterpillar
Location: Cairns Queensland Australia
March 24, 2013 6:36 am
Hi,
I would love if you could identify this caterpillar for me. It was found on my Kafir Lime Tree in Cairns, Tropical North Queensland, Australia. It is currently the end if the Wet Season, or the beginning of the Sourhern Hemisphere Autumn.
Signature: Scott Duncan

Hi Scott,
Initially we thought this was an Orchard Swallowtail Caterpillar, but your individual lacks the fleshy bumps characteristic of the Orchard Swallowtail Caterpillar, so we did some additional research and found the Fuscus Swallowtail, Papilio fuscus, pictured on Butterfly House website where it is described as:  “green or brown, mottled with orange, green, yellow, and white, and has a white line along each side. The thoracic and the final abdominal segment each have a pair of conical lumps. The thorax is humped.”  Butterfly House also indicates:  “The species occurs in the tropical coastal areas of Australia, as several races” with the Queensland subspecies being Papilio fuscus capaneus.  It appears this is a new species for our site, so were curious if perhaps we had some individuals misidentified as Orchard Swallowtail Caterpillars, but in checking, we have no other Fuscus Swallowtail Caterpillars on our site.  Only the adult and not the caterpillar is pictured on the Brisbane Insect Website.  The red horns pictured in your photo is a scent organ, normally concealed, known as the osmeterium.  When the caterpillar is disturbed, it reveals the organ that produces a scent thought to repel predators.  The organ might also give the caterpillar the appearance of a snake which could startle a bird into fleeing, rather than trying to eat the caterpillar.  Many Swallowtail and Birdwing species have caterpillars that possess an osmeterium.