The swallowtail butterflies form the family Papilionidae (550 species). They are large, colorful butterflies. The majority are tropical, but members of the family are found on all continents except Antarctica. This family includes the largest butterflies in the world, the birdwing butterflies of Australasia (genus Troides).
Swallowtails vary from all other butterflies in a number of anatomical traits. Most notably, their caterpillars possess a unique organ behind their heads, called the osmeterium. Normally hidden, this forked structure can be everted when the caterpillar is threatened, and used to emit a foul-smelling secretion containing terpenes.
The genera of extant swallowtails are usually classified into three subfamilies, Baroniinae, Parnassiinae and Papilioninae, the latter two being further divided into tribes. An additional subfamily Praepapilioninae, has a single extinct member, known only from a single fossil.
The Oregon Swallowtail Butterfly is the state insect of Oregon; the eastern tiger swallowtail is the state insect of Virginia.