A Defensive Citrus Swallowtail caterpillar - showing Osmeterium
The osmeterium is a defensive organ found in all papilionid larvae, in all stages. 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, small spiders and mantids. 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
''Papilio anactus'', the dainty swallowtail, dingy swallowtail or small citrus butterfly is a medium-sized butterfly from the family Papilionidae, that is endemic to Australia.
For protection against predators, this non-poisonous butterfly mimics the poisonous male ''Cressida cressida'', another swallowtail butterfly that obtains its toxic properties through its host plant, the Dutchman's pipe.