Black Swallowtail Butterfly Caterpillar Diary

Can you find nine caterpillars in this photograph? Hint: If you can’t, the smallest one is circled in the Additional Photos gallery below.

This year, we (mostly Beverly) have planted a wildflower/pollinator/herb garden outside our sunroom. In addition to the beauty of the flowers, we enjoy watching the butterflies, bees, and birds that frequent the flowers. Early in the summer Beverly found some Black Swallowtail Butterfly caterpillars on the dill and parsley plants.

The female butterfly lays individual eggs on the preferred plants of the species: the Monarch Butterfly only lays eggs on Milkweed plants while the Black Swallowtail Butterfly prefers dill, parsley, rue or fennel. After the egg hatches, the Black Swallowtail Butterfly caterpillars proceed through five stages called instars. They completely transform, going from a small black caterpillar with a white band to a prickly orange, white and black form. Next they go to a black, green, yellow and white-striped caterpillar that are often confused with Monarch caterpillars.

The following is a summary of the caterpillar activity on several herb plants in this garden:

July 9, 2019:

Beverly called me to see some caterpillars on the dill and parsley plants. She had already looked them up and identified them as the caterpillar stage of the Black Swallowtail Butterfly, also called the Eastern Swallowtail Butterfly. I came outside with a camera to see them and tried to take some pictures with my telephoto lens, with limited success.

July 10, 2019:

In an attempt to get better photos, I rented a macro lens (used for close-up photography) for the weekend. I was able to photograph nine different caterpillars on the dill and parsley plants (there were more caterpillars but they weren’t in a place where I could photograph them). The results were so much better than my initial attempt that I decided to purchase a macro lens to use for these and other close-up photos.

July 11, 2019:

Took close-up photos of two caterpillars and ordered a Sigma 105mm macro lens.

After a few days, most of the caterpillars were gone. Either the large ones crawled off to form their chrysalis and make the transition to butterfly or they were eaten by predators. Occasionally we would see one or two caterpillars on these herb plants but nothing special.

August 10, 2019:

In the evening Beverly found seven caterpillars on the dill plant.

August 11, 2019:

In the morning I went outside to photograph the caterpillars on the dill plant before they were in direct sunlight and found 10 caterpillars of different sizes on different parts of the plant. I was able to photograph one group that I initially thought was eight but after I viewed the photos on my computer, I realized there were really nine – the largest was about 2″ long and 3/8″ across and there was a very small one, about 1/4″ long, in the background. I took more photos in the late afternoon after the plant was in shadow, including the featured photograph. Later, Beverly saw a Black Swallowtail Butterfly on the parsley and she found several eggs which we hadn’t seen before. We will watch these eggs to see what develops.

August 12, 2019:

The dill plant has been almost entirely eaten by these voracious feeding caterpillars, so Beverly bent some of the branches so they could transfer to the adjacent parsley plant.

August 13, 2019:

There were several very small (about 1/8″ and 3/16″ long) caterpillars on a parsley plant. They are very difficult to photograph because the lens must be so close that keeping all of the caterpillar in focus is nearly impossible. I was able to get acceptable (but not good) photos of the two small caterpillars and one of the eggs.

August 15, 2019:

After heavy rains the previous afternoon and evening, there were many fewer large caterpillars on the parsley plant. We believe they probably crawled off to form their chrysalis and make the transition to butterfly.

August 16, 2019:

We decided we would transplant one of the parsley plants with a single medium sized caterpillar and some eggs into a pot and bring it inside so we could watch it grow and mature, and we moved the remaining large caterpillar on another plant to this one. We had previously purchased netting to be able to control their wandering so I made a frame to cover the potted parsley plant and the two caterpillars on a table in the Sunroom. A short time later I saw the larger caterpillar moving across the Sunroom floor – they can move surprisingly fast when they’re not busy eating. We got the caterpillar back onto the plant and secured the netting so it couldn’t escape again.

August 17, 2019:

Apparently the ‘escapee’ was ready to pupate – it has attached itself to a parsley stem with a fine silk strand (like a telephone lineman hangs on a pole with a belt) and with a patch of silk at its base to form its chrysalis.

August 18, 2019:

This morning the large caterpillar has formed its chrysalis, which is green to match the stem it’s hanging from.

August 19, 2019:

In addition to the chrysalis and the medium sized caterpillar (which is now large), today we found five small (1/8″ to 3/16″) recently hatched caterpillars on the indoor parsley plant plus one that is about 3/8″ .

August 20, 2019:

This morning we found four chrysalis stage attached to various parts of our house near the garden (three are green and one is brown). From the perspective of a crawling caterpillar, these are quite a distance from the host plant (25 or more feet). In the indoor enclosure, the second large caterpillar is wandering around the inside of the net, apparently looking for a place to pupate. This evening, the second caterpillar has attached itself to one of the PVC tubes of the frame for the net. Since there are no caterpillars crawling around, we removed the net and carefully counted the small ones – there are 14 on the parsley plant, ranging from 1/8″ to 3/4″ long.

August 23, 2019:

This morning Beverly noticed that one of the chrysalis on the house near the Sunroom had turned brown. This evening, she saw a butterfly on the brown chrysalis and we found a fifth brown chrysalis attached to the house.

August 24, 2019:

Early this afternoon a butterfly emerged from the chrysalis that had turned brown yesterday. We watched it for a while and within two hours it had flown away.

August 25, 2019:

Today, after a quick count, we found at least 23 caterpillars ranging in size from 3/16″ to large on the remaining outside parsley plant. We also found three small (1/2″) caterpillars plus some eggs on one of the milkweed plants in the garden. We believe they are Monarch caterpillars but will have to let them grow larger to be sure.

August 27, 2017:

This morning the last green chrysalis on our house has turned brown. Two hours later the butterfly has already emerged and is drying its wings. We now have 17 caterpillars on the indoor parsley plant and it is rapidly being devoured. Later in the day, we saw one of the large caterpillars from the outdoor parsley plant crawling up the brick wall of the house. It crawled all over the wall for several hours before settling down as dark approached. We didn’t see any monarch caterpillars on the milkweed plant.

August 28, 2019:

The wandering caterpillar has attached itself to the wall to start the chrysalis stage.

August 29, 2019:

The first chrysalis on the indoor parsley plant was a little darker this morning. An hour later the butterfly had already emerged, 12 days after starting its chrysalis stage. We found a Monarch caterpillar on the milkweed.

August 30, 2019:

The indoor parsley plant has been nearly devoured by all the caterpillars. We moved the plant outdoors and shifted some of the caterpillars to the remaining outdoor parsley plant but kept the last chrysalis on the PVC tube inside, waiting for the butterfly to emerge.

September 2, 2019:

We’re leaving today for a two-plus week trip to Montana and Wyoming so we took the last chrysalis outside – more about that trip later.

Additional Information

How to Raise Eastern Swallowtail Butterflies at Home

Raise Black Swallowtail Butterflies Indoors

Additional Images

Technical Information