We recently did a very homeschoolerish thing: We captured a caterpillar to watch it transform into a butterfly. My son is obsessed with the book The Very Hungry Caterpillar, and when we discovered a host of black swallowtail caterpillars demolishing my parsley patch, I figured it was a good time to try this experiment.
What We Did
The first step in our caterpillar-farming journey was not really intentional—I just wanted to grow some parsley. I planted a little patch a couple of years ago, and I’d noticed a few caterpillars appearing in the area. But I didn’t put two and two together until my girls and I were studying a section of our botany book that discussed the plants certain butterflies prefer as caterpillars. For the black swallowtail, parsley is definitely one of them! I never saw any actual swallowtails around the patch (laying eggs), but we counted at least twenty caterpillars at one point in my 2 square feet of parsley . . . and those were just the ones big enough to spot easily. Put simply, if you want any parsley left for yourself, you’d better grow a second patch.
Fortunately, I wasn’t using the parsley very often myself, so I left the caterpillars to it. One day, my kids discovered a caterpillar hanging off the nearby side of the house. They were quite concerned, but we soon realized that it was only preparing to go into its chrysalis state, which it did soon after (within about a day). I’d been a bit nervous about accidentally killing anything I took inside, but seeing this, I figured if a caterpillar can pupate on the siding of a house, it can probably figure it out inside a jar.
So, I cleaned out a large plastic jar, dug out a small section of parsley, and planted it inside, adding a few sticks. Then we captured three caterpillars: one tiny, one medium-sized, and one nearly full-grown. The idea was to watch them through multiple stages of growth, but unfortunately this plan didn’t work out since the smaller two caterpillars mysteriously disappeared after a few days. I’m still not sure what happened, but I’m guessing they weren’t hardy enough for the altered environment. Oh well. The large caterpillar survived and was dubbed “Jackson” by my son (whose best friend and favorite cousin happen to share this name). We placed some cheesecloth over the top of the jar, secured it with a rubber band, and waited for the magic to happen.
Different sizes of caterpillars: the top and bottom are the smaller caterpillars we captured (and apparently killed), and the middle is a bonus found outside. Notice the size of the top caterpillar as compared to my 5-yo’s thumbnail above it!
After a few days, we found Jackson the Caterpillar hanging off a branch by two tiny threads, curled into a J-like shape much like our little friend on the siding outside. He changed into his chrysalis clothes later that day when we weren’t watching, but we enjoyed watching this video of what it probably looked like.
Jackson the Caterpillar in his jar
Left: outside chrysalis within a day of when it was formed; right: our caterpillar’s chrysalis the night before hatching. The little blob underneath each chrysalis is the caterpillar’s leftover shed skin.
I didn’t do a great job of keeping track of how long he stayed in his chrysalis, but it was somewhere between 8 and 10 days. At some point, I got concerned that having the whole parsley plant in the jar wouldn’t give him enough room to spread his new wings, so we carefully removed his chrysalis stick and cleared out most of the jar before replacing it. The night before he emerged, we noticed that his black wings could be seen through the shell of the chrysalis. We hoped to catch him coming out, but he must have gotten to work before we woke the next morning. By the time we discovered him, his wings were fully spread and ready to go, and he was vigorously attempting to climb and escape the walls of his jar. We took him outside and removed the cheesecloth, and he fluttered out so quickly that I couldn’t get a picture. We hoped he would stick around and check out our flowers that many tiger swallowtails enjoy, but apparently he had other places to be!
Jackson the Butterfly!
What We Learned
Besides learning about the process of caring for the caterpillar, this experiment was educational in several ways. First, there was the obvious benefit of watching the different stages of the caterpillar life cycle. Even though we didn’t witness the actual moments of transformation, it still made it more real to know that this particular caterpillar formed this chrysalis and became this butterfly. Jackson the Caterpillar was very clearly the same creature as Jackson the Butterfly.
It was also interesting to see each step up close: from fat caterpillar, to hanging pre-pupate, to chrysalis, seeing the change in the chrysalis, and then seeing the butterfly. We’ll definitely have to try again another time since I think watching the butterfly emerge and spread its wings must be the most fun part. The above-mentioned video of the caterpillar forming the chrysalis is also quite fascinating, though. My girls and I didn’t realize that the chrysalis actually forms under the caterpillar’s skin which is shed off like an outer coating.
We also had fun (at the poor caterpillars’ expense) learning about their defense mechanism: sticking out two bright, antenna-like appendages from their heads. Evidently this appendage is called the osmeterium, and not only does it look rather startling, but it produces quite a nasty odor. My back-up theory for why the younger two caterpillars died is that they got stink-bombed to death when my son upset the larger caterpillar a bit and caused him to emit this foul smell. We left Jackson alone after that and bothered another caterpillar in the garden. We found that a couple gentle touches would bring out the osmeterium somewhat, but continued harassment caused the caterpillar to extend it to its full length, plus the caterpillar reared up on its hind end. Though ultimately harmless, it succeeded in looking rather intimidating!
Progression of a caterpillar showing off its osmeterium.
We also learned a bit about how to tell a male from a female black swallowtail. I warned my son that there was no guarantee that “Jackson” was actually a male, but after his metamorphosis and some study of pages like this one, we noticed that he had wider bands of yellow and smaller sections of blue on the back of his wings. Thus, we were reasonably certain that changing his name to “Jacqueline” would not be necessary.
It was a memorable and educational experiment for sure. Have you ever raised a caterpillar with your children? If not, this page has some helpful tips to get you started!
Photo Credit: Photos courtesy of author.