Distribution
"Papilio anactus" is endemic to Australia. It was originally only present in New South Wales, Victoria and Queensland, but due to the growing of citrus, a larval food plant of this species, in orchards, the species spread to South Australia in the late 1920s. "Papilio anactus" is not present on Kangaroo Island or elsewhere in Australia, as there are currently too few citrus trees.It also occurs on New Caledonia. There, it may be an introduced species or a vagrant.
![A Defensive Citrus Swallowtail caterpillar - showing Osmeterium The osmeterium is a defensive organ found in all papilionid larvae, in all stages.[1] The organ is situated in the prothoracic segment and can be everted when the larva feels threatened. The everted organ resembles a fleshy forked tongue (not unlike a snake tongue), and this along with the large eye-like spots on the body might be used to startle birds and small reptiles. The osmeterial organ remains inside the body in the thoracic region in an inverted position and is everted when the larva is disturbed in any way emitting a foul, disagreeable odor which serves to repel ants,[2] small spiders[3] and mantids.[4] To humans, this odour is rather strong but pleasant, usually smelling like a concentrated scent of the caterpillar’s food plant and pineapple.
The constitution of the osmeterial secretion varies from species to species and contains monoterpene hydrocarbons, sesquiterpenic compounds or a mixture of aliphatic acids and esters
https://en.wikipedia.org/wiki/Osmeterium Australia,Dainty swallowtail,Geotagged,Papilio anactus,Summer](https://s3.amazonaws.com/media.jungledragon.com/images/4568/111918_small.jpg?AWSAccessKeyId=05GMT0V3GWVNE7GGM1R2&Expires=1759968010&Signature=6b18xr4pon5O8bA9kmuBXlfVlFs%3D)
Reproduction
The first instar is dark, with two rows of short, bristly spines. The anterior parts have broad yellowish bands, black head, with some short hairs, the first three instars retain this. Later instars have a white upside-down V mark on the front which becomes most visible in the last instar. The fleshy spines also become less bristly in later instars, and towards the last instar is almost absent. After emergence the immature larva eats the egg shell, before moving on to eat new leaf shoots. Later instars eat fully developed new leaves, but not usually matured leaves. In warm areas the larvae go through five instars, and larvae in cold areas can have six instars before developing to a pupa.Mature larvae are about 35 mm long, generally black, with two subdorsal rows of fleshy black spines, and sublateral and lateral rows of large orange or yellow blotches, and numerous small, light blue and white spots. The strength of yellow can vary, and some larvae can be a strong yellow or pale. The amount of orange can also vary, and it can be absent. There are subdorsal blue dots on the anterior part of the larva. The head is large, black, with a white upside-down v mark on the front.
When disturbed, the larvae can erect a reddish-orange coloured, osmeterium from behind the head which releases a citrus-like smell of rotting oranges. This smell acts as a repellent to predators. The larvae attempt to throw their heads either backwards or sideways if a predator attacks because it is more effective if the chemical hits the predator. The secretion is usually composed of an irritant butyric acid. The osmeterium is exists in all stages of the larvae.
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