What kind of bug am I?
These caterpillars have eaten my Fennel Plant. Are they future butterflies?
There are two very similar looking Swallowtail Butterfly Caterpillars with nearly identical food plants. The Anise Swallowtail, Papilio zelicaon, is found in the Western U.S. The Black Swallowtail, Papilio polyxenes, is found in the east. Depending upon your location, your caterpillar is one of these, though our guess is the Anise Swallowtail.