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Wingspan 80-90mm. A large tailless swallowtail that is mostly creamy yellow and black. Sexes alike. In freshly emerged specimens, the cream yellow is almost fluorescent, but this lovely brightness gradually changes into a dull rusty orange with age.
Status, distribution and habitat
It is found all over the island except in the highest hills. Individuals are seen throughout the year but their populations peak before the onset of the heavy monsoon rains. Though reportedly a pest in some countries, it has not been recorded to reach pest status in Sri Lanka. It is a butterfly of the open spaces and prefers full sun to partial shade.
It is a common, widely distributed butterfly that occurs all over the island. It is found wherever its larval host plant, citrus, grows. It is not a butterfly of the high canopy and is more likely to be seen on low bushes and shrubs. It flies very fast around noon, being somewhat sluggish in the early morning hours. The male frequently settles on wet soil, often keeping his wings in motion, ready to fly away if disturbed. Both sexes visit flowers with delight where they will spend a few fleeting seconds before moving on to the next flower. While feeding, they keep their wings in rapid motion, only occasionally keeping them still, particularly the older specimens that are probably tired and weary. They rarely visit Eupatorium odoratum, which is popular with many other species of swallowtails.
The larva feeds on the members of the Rutaceae - the citrus group being its favorite. Like many in its group, the newly emerged larva perfectly resembles a fresh bird dropping. This camouflage is so good that a first instar larva can remain safely on top of the tender leaves, in clear view of its predators.
As the larva becomes larger, the bird dropping strategy becomes less effective, and in the second instar, the larva changes its strategy. It now takes on the green colour of its surroundings, and for further protection, moves towards the center of the plant to hide itself from predators.
When the camouflage strategy fails, and the larva is pecked at, the next strategy kicks in, which is to scare away the predator. To achieve this goal, the larva has a head that looks like a snake's head, complete with eyes and other markings. An organ called the osmetrium, located just above the head, plays the role of the snake's tongue, and it is usually tucked away inside the skin and concealed. When the larva is disturbed, it moves its head in a quick jerk, pushes out the osmetrium, and emits a foul smelling odor - all designed and coordinated to resemble a snake rearing up to strike. The snake strategy is most effective when it takes the predator by surprise; it achieves this by remaining very still and well camouflaged among the lower foliage of the plant, and then rearing up suddenly to make its presence known.
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