Swallowtail butterflies are large and colorful butterflies which form the family Papilionidae. There are at least 550 species, and though the majority are tropical, members of the family are found on all continents except in Antarctica. The family includes the largest butterflies in the world, the birdwing butterflies of Australia-genus Ornithoptera.
Swallowtails is different from all of 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 emits smelly secretions containing terpenes. The adults are often tailed like the forked tail of some swallows, giving the insect its name.