No, that is not a Monarch caterpillar on your parsley plant.
July 16, 2011 § 4 Comments
I am often asked “why is that green, yellow, and black Monarch caterpillar eating my parsley”?
Chances are, you will never see a Monarch caterpillar on your parsley. By far and away it is more likely that you have the caterpillar of the gorgeous Black Swallowtail Butterfly (Papilio polyxenes).
Caterpillars that are actively feeding are usually only found on their larval host plant(s), the plant they have developed a distinctive coevolutionary relationship with over millennia. Monarch caterpillars do not eat parsley and Black Swallowtail caterpillars do not eat milkweed, and if either attempted, they would not survive. Black Swallowtails were in the past commonly referred to as the Parsnip Swallowtail as their caterpillar food plants belong to members of the Umbelliferae, or Carrot Family. The diet of the Black Swallowtail caterpillar includes the foliage and flowers of carrot plants, fennel, dill, parsley, Queen Anne’s lace, and parsnips.
The Monarch caterpillar is yellow, black, and white. The Black Swallowtail caterpillar is green, black, and yellow.