Giant Swallowtail (Papilio cresphontes)
Giant Swallowtails are common in Texas, where I photographed this one, and throughout the deep southern US. In most of North Carolina, Giant Swallowtail is very rare or absent. It is easiest to find, but still not common, along the southern coast.
Santa Ana NWR, Hidalgo Co., TX 10/15/04.
This may be a first instar caterpillar — it was tiny! When touched, Giant Swallowtails unfurl their very stinky stinkhorns from their head as a discouragement to predators. Their host plants are various species in the Rutaceae, the Citrus family, such as Zanthoxylum (as here).
Boca Raton, Palm Beach Co., FL 6/28/2010.