Eastern Black Swallowtail Butterfly

The eastern black swallowtail butterfly, Papilio polyxenes, is without question one beautiful butterfly. But despite its good looks, the black swallowtail isn’t always a welcome sight in backyard gardens.

As things go with a number of problematic bugs, it isn’t the adults that are the problem. Rather it’s their offspring and their choice of host plants. With the eastern black swallowtail, the problem is evident in some of its other common names, like parsley swallowtail. More on that in a bit.

And to be fair, the problems the eastern black swallowtail might cause are far outweighed by the beauty it brings.

Some basics:

— Eastern black swallowtails are native to Florida and, as the name suggests, are found over most of the United States this side of the Rocky Mountains, south into Mexico, Central America and South America.

— There are multiple subspecies of the eastern black swallowtail; the variety found in Florida is known as asterius.

— As the name also suggests, they are mostly black with an array of yellows, blues, oranges and reds. They are fairly large as butterflies go with wingspans between 3.1 inches to as much as 4.25 inches. Females generally are larger than males. The upper side of the wings has two rows of yellow spots, larger and brighter in males than females. The hind wings are each marked with a single red spot with a black bullseye inside.

The underside has two rows of orange spots separated by a row of powder blue marks.

— Larvae, or caterpillars, are mostly black with a prominent white “saddle” in the middle, picking up white and green bars along its body as it develops. The effect is to make the kids look like bird poop and distasteful to predators.



They also have branched black spines each with an orange base, along their backs.

— The problem with eastern black swallowtails, as noted above, is their choice of host plants — members of Apiace, the carrot family. And yes, females will lay their eggs singly on the leaves of carrots, along with parsley, parsnips, celery, dill and caraway seeds.

They’re not an economic threat to commercial farming, but they could wreak a bit of havoc on a small backyard garden. According to the University of Florida, if they show up in your garden, chemical warfare isn’t warranted. Rather pick off the offending larvae, manually.

Native host plants found in Florida include mock bishopweed, spotted water hemlock and water cowbane.

Nectar plants include milkweeds and thistles, as in the purple thistle that the eastern black swallowtail is feeding on in the photos shown on this page.

As we noted above, the larvae use their poop-like looks as a form of defense. The adults do likewise, practicing Batesian mimicry. What is Batesian mimicry? It’s taking on the looks of something poisonous or distasteful. In the case of the eastern black swallowtail it’s sharing the basic color pattern of the poisonous pipevine swallowtail. Our guy isn’t poisonous to birds and other vertebrates but the pipevine swallowtail is. Birds that have tasted a pipevine swallowtail will associate our guy with the poisonous guy and leave it alone.

Eastern black swallowtails spend a lot of their time perched with their wings folded up, maximizing their similarity to the pipevine swallowtail.

If you’re wondering, the scientific name, Papilio, means butterfly; Polyxenes is the name of the daughter of Priam, the legendary king of Troy during the Trojan War.

Other common names for the eastern black swallowtail include black swallowtail, parsnip swallowtail, American swallowtail, celery worm and caraway worm. It is a member of Papilionidae, the swallowtail family.

Jonathan Dickinson State Park