Eastern Black Swallowtail Caterpillar - Papilio polyxenes
The larvae of this species changes color quite dramatically with each molt. Early instar caterpillars are only about 1 cm long and are bird-dropping mimics. They are mostly black, spiky, and have a white saddle around their middle. The white saddle is caused by uric acid deposits that may function as an antioxidant, protecting the larvae from phototoxic chemicals in their host plants. It was about 1 cm long.
When provoked, the larvae of this species sprout eversible orange horns called osmeterium, which release a foul odor in order to deter predators. The osmeterium is a defensive, glandular organ that is coated in stinky chemicals, and is located at the base of the caterpillar's head. The osmeterial odor changes between species and within the life stages of the caterpillars.
I spotted this caterpillar on fennel (Foeniculum vulgare) in a rural garden.
The Black 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".
