The Development of the Eastern Black Swallowtail caterpillar

The Eastern black swallowtail caterpillar is a fascinating creature to watch. After my little experiment to see whether I can get the caterpillars to take on a different type of plant, I continued to watch them grow. I wanted to see how far the caterpillars would grow and whether they will reject the parsley offered to them.

Eastern Black Swallowtail caterpillars go through several stages of shedding their skin as they grow. This stage between the process of shedding and forming into a renewed caterpillar is known as “instar”. There are five instar stages that the caterpillar will go through.

First Instar

At the first instar stage, the caterpillar emerges from its shell. It will proceed to eat their shell. Depending on their appetite, sometimes the entire shell is eaten. The caterpillar will begin explore around the one leaf and then later proceed to feed on it. At the first instar, the caterpillar does not travel far from the leaf it sits on. The coloring will turn lighter as it matures.

Second Instar

At the second instar stage, the caterpillar will shed its dark exoskeleton and emerge with reddish-brown spikes. Initially, the caterpillar appears dark with light colored spikes. The caterpillar will eat the skin after they molt. As they matures, their spikes will darken, and the body turns into a darker color with beautiful brown spots developing on their sides. Some of the brown spikes seen to have receded into the spots.

Third Instar

The third instar of the caterpillar will look similar to its second instar. The body is still dark and the striped bands on the body are clearly defined. Initially, the spikes are reddish-brown but will turn black as it matures. You will find white spots developed on its lower sides.

Fourth Instar

The fourth instar is most dramatic change in size and color. The caterpillar at this stage grows much bigger. It emerges with lots of black and white bands around its body and again with lots of orange spikes. As it matures, the spikes seem to recede a little. Some of the caterpillars white stripes turn yellow and their bodies are a mix of yellow, white and black bands. Brown spots are now clearly bright orange-yellow and clearly defined across some of their white stripes.

Fifth Instar

The fifth instar is the last stage before the caterpillar will enters its pupa stage. At this stage, it is much larger. Their appetite is ravenous. There is a feeding frenzy prior to its transformation in order to build enough energy for the trip. The body is smooth with green and black stripes. There is no appearance of any spikes as it emerges from the exoskeleton. The color is already defines when it sheds the exoskeleton and the green and black stripes does not change color as it matures. In this stage, their only job is to get bigger.

The Caterpillar’s Face

Prior to the caterpillar getting ready to enter the next instar, the “face” begins to drop lower and lower until it is nearly hanging afloat.

During the transformation into the next instar stage, the caterpillar will shed this “face” and develop a new one. Their face is “blind”, there are no eyes but it will take only a few seconds for the new “face” to form.


Finally, I want to show the caterpillar in the fourth instar emerging and eating its shedded layer. This happens after each stage of emergence. After shedding its’ skin, the caterpillar will rest until the lines of its’ face is darkened.

Immediately after their “face” coloring is formed, they turn around and clean up by eating their exoskeleton.

It’s rare that I will find exoskeletons left behind. But sometimes the caterpillar forgets to clean up.

It’s Not Over … Read my blog as I follow the Metamorphosis of the Eastern Black Swallowtail.

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