Swallowtail butterflies are large, colorful butterflies in the family Papilionidae, which includes over 550 species. Though the majority are tropical, members of the family occur on every continent except Antarctica. The family includes the largest butterflies in the world, the birdwing butterflies of the genus Ornithoptera.
Swallowtails have a number of characteristic features; for example, on the prothorax a Papilionid caterpillar bears a repugnatorial organ called the osmeterium. The osmeterium normally is hidden, but when threatened, the larva everts it through a transverse dorsal groove by inflating it with blood. It is a fleshy, forked structure and emits smelly secretions containing terpenes, which the larva typically tries to smear onto any attacker touching it.
The adults of some species have conspicuous posteriad prolongations of the hind wings in the region of the M3 vein. The forked appearance of these features as seen in the butterfly when resting with its wings spread, gave rise to the common name swallowtail. As for the formal name, Linnaeus chose Papilio for the type genus, Papilio being the Latin for a butterfly. For the specific epithets of the genus, Linnaeus applied the names of Greek heroes to the swallowtails. The type species: Papilio machaon honoured Machaon, one of the sons of Asclepius, mentioned in the Iliad.