Echinacea Black Swallowtail female by Lori Athey

Eastern Black Swallowtail Butterfly

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

How do you tell whether a Black Swallowtail butterfly is male or female?

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.

What butterflies look similar to the Black Swallowtail?

This butterfly mimics the appearance of the poisonous Pipevine Swallowtail.

What do these butterflies eat?

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).

How can I find their eggs?

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.

How do you identify a Black Swallowtail caterpillar?

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

As do other swallowtails, this butterfly 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 the 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.

How do you identify the butterfly chrysalis?

The chrysalis can be green or brown.

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

How do Eastern Black Swallowtails survive the winter?

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.

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