The larva of the Black Swallowtail Butterfly (Papilio polyxenes) goes through several stages and where their apperance changes. This picture here is during the third instar stage…
The eggs of the Black Swallowtail are typically laid on garden plants from the carrot family, including dill, fennel, Queen Anne’s lace, and parsley.
He’s a good bug, despite the fact I found him feasting on my carrot greens. No real harm was done. The Carrots are doing great and now there are beautiful Black Swallowtail Butterflies in the garden.