Metamorphosis of the Eastern Black Swallowtail Butterfly

From my previous blog, “The Development of the Eastern Black Swallowtail”, we see the caterpillar has grown and it is now at the fifth instar. The caterpillar will eat ravenously the entire parsley stem it sits on. It will travel from stem to stem to feed, first on the leaves, and then eating down the stem.

Restless Wandering

At some point, the caterpillar stops feeding and begins to wander. It will travel a great distance, (although in my butterfly netting, it was going around in circles for over a few hours), in search for a proper place for the transformation. Once it has found a spot in which it can settle to make its chrysalis, it begins by expelling all the remaining ingested parsley bits and water from its body.

Spinning silk

After a short rest, it begins to spin a silk around its body, pulling the silk from left to right and backwards until it is secured in place. At the same time, its lower end spits out a patch of sticky silk to help secure the lower body into place. I think this sticky patch could be the same material that helps it stay on the plant stems during its instar stages. Somehow, the caterpillar is able to release and take back this stickiness while it sits on the plants.

Once it is done pulling the silk, it will remain in place and begins to morph underneath the skin. As it settles in position, its tail will become pointed and the body will begin to curl in. You can see in the pictures below the early stages of transformation where the caterpillar body is still very green. In the second picture, you can see the transformation to a chrysalis underneath the thin skin. —Check out the video at

Ready for a big change

When the caterpillar is ready to shed its exoskeleton, you will see a line of liquid “milk” burst from the tail end of the caterpillar to the upper part of the body (noted in red below). Once this liquid burst is complete, the caterpillar will begin to tear away its skin to reveal a chrysalis underneath. It will wiggle away the shedded skin and then begin to settle into its final transformation. — Check out the video at

Green or Brown?

The chrysalis will be in one of two colors: brown or green. There doesn’t seem to be a reason why it would choose one color over the other. I have found chrysalis in both color side-by-side. The third picture below will show you the transparency of the the chrysalis that will be ready to hatch very soon. If you look closely you will see the orange spots that appears on the butterfly.

Here it comes!

The pupa shell will turn dark and translucent when the butterfly is ready to emerge from its shell. This coloring is due to the metamorphosis of the pupa inside to a dark butterfly. Most often, I found the butterfly will emerge out in early morning or afternoon, but never in the evening. I think it is because the butterfly requires the sunlight to provide warmth so its wings can dry. On one very hot day (it was almost 100-degrees), a butterfly emerged out of its shell but unfortunately, being in the very hot sun with no shade, its wings dried before it was able to uncurl it. It was horrible, the butterfly could not develop its wings and crawled about for a half day before it died. Since then, I always make sure that the pupa are located in shaded areas, so that I won’t repeat that experience.


The butterfly wings dried and it is ready to take flight. Looking closely at the wings will show you the veins that provide the powerful fluttering and the feathery edges. It looks like a layer of tiny feathers on its wings and a furry body.

They are beautiful

Each butterfly will have similar coloring of yellows, oranges, blues and distinctive markings. I was very concerned for the last two butterflies as they emerged in late September and the weather was very cold – the temperature was in the 50s. The two late-season butterflies clung to the flowers for two days, one through some cold, rainy weather which brought the temperatures down to the 40s. But luckily, one afternoon the butterflies flew away after the rain ended. The sun was out, and the butterflies were able to take flight. Although the temperatures that day were in the 50s, the sun provided the creatures enough warmth to be able to fly.

Here we go again.

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