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The swallowtail butterfly family, Papilionidae, consists of at least 550 species, many of which are large and colorful and recognizable even to non-specialists. While the majority of swallowtail species are found in tropical latitudes, representatives from the family can be found on every continent except Antarctica, and can be common in both tropical and temperate habitats. Swallowtail butterfly diversity is greatest in East and Southeast Asia, a region where many natural butterfly habitats are under extreme threat of destruction due to human activity. Some swallowtails, particularly representatives from the genus Parnassius, may fly at very high elevations. The birdwing butterflies (Troidini: Troides) of Australasia are the largest butterflies in the world. Collins and Morris (1985) provide an overview of the patterns of swallowtail diversity around the world.
The name "swallowtail" refers to a tail-like extension on the edge of the hindwing that is found in many, though not all, papilionids. The function of this tail is not known, but genetic studies in some species of Papilio suggest the tail is a labile character whose expression is controlled by a single gene (Clarke and Sheppard 1960, Clarke et al. 1968).
Within the Papilionidae, many families of larval hostplants are utilized, although five families generally dominate the host records: Aristolochiaceae, Annonaceae, Lauraceae, Apiaceae, and Rutaceae. Notably, the swallowtail tribes Zerynthiini (Parnassiinae), Luehdorfiini (Parnassiinae) and Troidini (Papilioninae) are limited almost exclusively to feeding on Aristolochiaceae. It has been demonstrated in a number of Aristolochia-feeders that caterpillars are able to sequester aristolochic acids, causing both the larval and adult stages to be unpalatable to predators (eg. von Euw et al. 1968).