Black Swallowtail caterpillar showing orange osmeterium partly everted - the defensive organ found in all stages of growth of papilionid larvae. It is everted when the larva feels threatened, perhaps as I had the macro lens a little too close!
The everted organ resembles a fleshy forked tongue not unlike a snake tongue and this along with the large eye like spots on the body might be used to startle birds and small reptiles.
The Black Swallowtail , also called the American Swallowtail or Parsnip Swallowtail, is a butterfly found throughout much of North America. It is the state butterfly of Oklahoma. An extremely similar-appearing species, ''Papilio joanae'', occurs in the Ozark Mountains region, but it appears to be closely related to ''Papilio machaon'', rather than ''P. polyxenes''.