Today, I was planting hard garlic for next year's crop when I found these caterpillars on my fall-winter crops of Carrot and Fennel. I identified these caterpillars were the larvae stage of the Eastern Black Swallowtail Butterfly(Papilio polyxenes asterius). The Eastern Black Swallowtail Butterfly is one of our most commonly studied swallowtails. Although it is admired for its beauty, it is one of the few butterflies that may occasionally be considered a pest. Various other names have been known, including black swallowtail, American swallowtail, parsnip swallowtail, parsley swallowtail, celery worm, and caraway worm.

Although black swallowtail caterpillars feed on a number of cultivated plants, they are never sufficiently common to cause a problem in commercial agriculture. If control is required in home gardens, hand-picking is recommended. If hand-picking is impractical, either a foliar insecticide or the bacterial insecticide Bacillus thuringiensis provides effective control. Also, numerous insect predators and wasp and fly parasitoids of the caterpillars provide some natural control.

Sources:

Miller JY. (editor). 1992. The Common Names of North American Butterflies. Smithsonian Institution Press. Washington, D.C. 177 pp

https://entnemdept.ufl.edu/creatures/bfly/bfly2/eastern_black_swallowtail.htm (Collected on 9/25/2022)