Eastern Black Swallowtail

Eastern Black Swallowtail (Papilio polyxenes), also sometimes referred to as “parsley worms,” are common in Delaware.

The butterfly mimics the appearance of the poisonous Pipevine Swallowtail.

It’s pretty simple to tell the males and females apart. The males display a distinctive band of yellow spots, while the females have smaller yellow dots and prominent blue coloring.

They lay round, cream-colored eggs singly on a variety of plants in the carrot family, including parsley (Petroselinum crispum), dill (Anethum graveolens), fennel (Foeniculum vulgare), common rue (Ruta graveolens), Golden Alexander (Zizia aurea), and Queen Anne’s lace (Daucus carota, or wild carrot).

The egg’s appearance changes to yellow with a dark ring and then to black as the caterpillar gets ready to emerge (about a week, shorter if it’s very warm, or longer if it’s chilly).

When it emerges, the caterpillar will eat its egg for its first meal.

Unlike other commonly recognized caterpillars, like the Monarch, the Black Swallowtail looks different every time it sheds its skin, or exoskeleton (which it also will eat for the nutrients).

As do other swallowtails, the Black Swallowtail will protrude a gland called the osmeterium when threatened. These look like little tentacles or horns and emit a foul-smelling odor as a defense mechanism.

One tell-tale sign that a Black Swallowtail caterpillar has finished eating and is preparing to pupate is a noticeable excretion of watery poop. Its body is purging everything it won’t need in the chrysalis.

It connects itself to a safe surface with a strong, silky string called a girdle.

The chrysalis can be green or brown.

Regardless, it will begin to become see-through when the butterfly is readying to emerge.

There are three generations of the Black Swallowtail in Delaware each year, and the last will spend the winter in its chrysalis until the following spring, when it will emerge as an adult.