The Carlisle Mosquito Online

Friday, September 22, 2006


Eastern Black Swallowtail (Papilio polyxenes)

The Eastern Black Swallowtail is a common butterfly in our area from March to September with a very interesting life span that can easily be watched first hand. Over the last few years I have had an enjoyable time raising and watching these caterpillars turn into butterflies and then releasing them back into the wild.

I first noticed the Swallowtail caterpillars when I thought I had bird droppings all over the parsley in my garden; on closer inspection they turned out to be living things that were less than 1/4 inch long, black-brown with a white area mid-center on their backs, and covered with spikes. A good picture of this first stage can be found at first inclination was to leave them on my parsley, but in a few days when they entered the next caterpillar stage and started eating all my parsley, I put them in a container with a sprig of store-bought parsley for each caterpillar.

A caterpillar terrarium

Caterpillars tend to stay where their food is until they are ready to pupate, so it is easy to contain and maintain them. A small terrarium with a screen top is ideal. Sprigs of parsley can be inserted in a small-mouthed container of water and placed on a paper plate. The water keeps the parsley fresh longer, and you can change the parsley and the paper plate as necessary. Another method is to lay paper towels on the floor of the terrarium and place the parsley on the paper towels. Make sure not to throw your caterpillars out when you change the materials.

In the second stage they develop black and white stripes with yellow spots on every other black band while retaining some of the black spikes they had in the first stage. They eat voraciously and need fresh parsley about twice a day. As they continue to grow, they will shed their skin and the white stripes will become greener in color. Notice the spikes in the picture above.

When they get to the third caterpillar stage, they are about two inches long, the white bands take on a yellowish-green tinge, and the spikes are gone, leaving a smooth caterpillar. In this stage the caterpillar starts to roam around and will crawl up the sides of the terrarium and across the top looking for a place to form a chrysalis.

Forming a chrysalis

As they form a chrysalis, they will attach themselves at the bottom and then work a finely spun sling around their body about two-thirds of the way up. Their size diminishes as they appear to scrunch up, and they may stay that way for a day. When the chrysalis is formed, it will look like a green leaf or a brown twig. If it is green, the caterpillar will emerge as a butterfly that same summer; if it is brown, they will over-winter in this stage and emerge next March through May. The owner of the Butterfly Place in Westford told me that the green chrysalis is rare. However, last year I had my first green one, and this year I had only one brown one, which hatched this season regardless of its color.

When the butterflies are ready, their chrysalis will darken, and within a day they will emerge and take about 15 minutes to unfurl their wings which appear pleated. Males (more yellow) have two rows of yellow spots near the wing edge, and on the lower wings they have a yellow band with a narrow blue band underneath. The females (more blue) have two rows of white-cream spots that are often faint on the upper wings. The lower wings have a wide blue band between the spots. See swallowtail.htm for good pictures of the male and female butterfly.

Releasing the butterflies

They can't fly for the first few hours so it is easy to transport them for release. Wait an hour and then place your finger in front of their front legs; they will step up onto your finger. Make sure all legs have stepped up before moving your finger away. I release my butterflies onto a butterfly bush. At this point they still like to hang from the bottom of the blossom, and by holding them close to the blossom they can step onto it.

This year I raised Monarchs (they like milkweed) and Eastern Black Swallowtails together — parsley to the left, milkweed leaves to the right. The two populations stayed by their food sources and didn't mix until it was time to form a chrysalis; then they all hung out together!

Other facts: the wingspan is 3 1/2 inches; its favorite caterpillar food is parsley, carrots, Queen Anne's Lace and dill; its favorite butterfly nectar is butterfly bush, fruit trees, echinacea, phlox, zinnias, and loosestrife; and its habitat is open fields, meadows, and gardens.

References: 1) Wikipedia, The Free Encyclopedia, Swallowtail. 2) Pyle, Robert Michael, National Audubon Society Field Guide to North American Butterflies. New York: Alfred A. Knopf. 1981. 3) Eastern Black Swallowtail. Study of Northern Virginia Ecology, Stratford Landing Elementary School.


Anyone can write the Biodiversity Corner about any living thing, animal or vegetable, that exists in the wild and was seen in Carlisle. Or tell Kay Fairweather what you've seen or send her a photo, and she will write the column.


2006 The Carlisle Mosquito