Last week I found some late stage, or instar, Black Swallowtail caterpillars on my parsley plants. I couldn’t believe that I missed seeing them earlier. If you have sunny, meadow-like areas nearby, as well as gardens with flowering perennials, there a good chance you’ll see them, as these are the larvae of the most common swallowtail butterfly in the United States. I’ve seen Black Swallowtails laying eggs on my Fennel (Foeniculum vulgare) and they may have laid eggs on my Parsley (Petroselenium crispum) too. Or I might have brought home these larvae on parsley I purchased from the nursery.
I put my pots of parsley with the caterpillars under a screened laundry basket to protect them from parasitic flies. Each one has now transformed into a grey pupa, or chrysalis, and will spend the winter there. I will release the butterflies in the spring after they eclose, or hatch into adults.
Both fennel and parsley are members of the carrot family (Apiaceae). Black Swallowtails also lay eggs on other members of this plant family, including Queen Anne’s Lace (Daucus carota) and Dill (Anethum graveolens). The larvae also feed on some members of the Rutaceae, or citrus family, such as Common Rue (Ruta graveolens). I find it interesting that some companies push insecticides to kill the “parsley worm” in the garden. Insecticides have no place in a wildlife garden for native bees and butterflies (not to mention on herbs that you plan to eat). Many homeowners are not aware of what a beautiful butterfly this larva will become. That’s why I say plant a little extra parsley for the Black Swallowtails.
Before other plants from this family were introduced in the United States for gardens, the traditional larval food plant in the region for swallowtails probably included two species of the Connecticut native perennial Golden Alexanders, including Common Golden Alexanders (Zizia aurea) and Heart-leaved Golden Alexanders (Zizia aptera).
Common Golden Alexanders is typically found in floodplains, meadows ,and on the shores of rivers and lakes. But Heart-leaved Golden Alexanders is rare in New England and is a state-listed endangered species in Connecticut. It loves calcium-rich, or calcareous, soils and in Connecticut has been found growing on precolonial Native American shell middens, which are piles of leftover oysters, mussels, and clams.
Black Swallowtails usually have two generations per year. After spending the winter as a chrysalis, the first generation hatches between late April and early June. The egg stage lasts four to nine days, the larval stage 10 to 30 days, and the pupal stage 9 to 18 days (in the first generation).
A Black Swallowtail caterpillar begins life with all the unappealing appearance of bird poop—all black with a white stripe across its midsection. Many butterfly larvae have early life stages that mimic bird droppings as a protection from predators. There is also mimicry in the adults. The color of the adult Black Swallowtail mimics the coloration of the Pipevine Swallowtail (Battus philenor), a toxic species, and therefore the Black Swallowtail gains some protection from bird predation.
Adult Black Swallowtails will come to a host of plants to find nectar, including native perennials such as Meadow Phlox (Phlox paniculata), Wild Bergamot (Monarda fistulosa), milkweeds such as Butterfly Weed (Asclepias tuberosa) and Swamp Milkweed (Asclepias incarnata), and annuals such as Zinnia and Cosmos.
Adult male butterflies can use lek mating, in which a bunch of males will wait near larval food plants for females and display there for them.
Through natural succession, many of Connecticut’s habitats eventually change over time and become mature forests. Meadows, however, provide key habitats for a host of species, including Black Swallowtails. You can add to or create your own mini-meadow in a perennial garden bed in your yard or neighborhood by planting Golden Alexanders and adding some parsley, dill, or fennel in the summer. Plant it and they will come.