Black Swallowtail caterpillar.

Caterpillars of black swallowtail butterflies, Papilio polyxenes, are various shades of green, with narrow black bands on each body segment. The black bands are interrupted by yellow-orange dots. The caterpillars, which can reach 2” in length, consume leaves and flowers of various plants in the carrot family (Apiaceae), including cultivated carrot, parsley, dill, and fennel. Older larvae often prefer the inflorescence. This species spends the winter in the pupal stage inside a chrysalis. The caterpillars have a forked, glandular process behind the head that can be everted to emit a strong odor distasteful to predators.