Wednesday, June 5, 2019

Butterfly Metamorphosis - Passive STEM Program

Metamorphosis from caterpillar to butterfly, butterfly STEM program

Eric Carle's beloved classic, The Very Hungry Caterpillar, was first released 50 years ago, on June 3rd, 1969. I used this, and the recent release of my new favorite storytime book, The Very Impatient Caterpiller, as an excuse to do an activity I've always wanted to do, getting caterpillars and watching them grow and metamorphosize into butterflies.

I thought this would be a great passive STEM program to do at the library that families would enjoy. We decided to do it in May rather than June, since summer is so super busy already, and it really didn't fit our summer reading theme. So I timed it to get the caterpillars in around my weekend to work in May, and used the family storytime to introduce them and kick it off. 

I ordered a kit from Carolina Biological Supply that included two cups with 5 caterpillars each (we actually got 6 each) and all the food they would need, a large mesh butterfly cage, cotton rope wick for feeding, and both print and online resources that included general information, care instructions, activity sheets, and more. They are a little more expensive, but this is a well-established scientific company with an excellent reputation and their caterpillars seem to have a higher success rate.

(click on any photo to see full-size image)

The caterpillars come in 8 oz deli-style cups, which have perforated lids lined with cloth or paper (for the caterpillars to attach to later), and contain an artificial diet. Painted Lady caterpillars are the only ones to thrive on an artificial diet, which makes them much easier to raise, and reduces the chance of disease. I let everyone who attended the Caterpillar Storytime look at the caterpillars up close, then placed the cups inside a screen-covered aquarium for protection, and placed them on a shelf next to the desk, along with an information sheet and diagram of the life-cycle. I updated the info sheet at each stage in the process.

Painted Lady caterpillars

And then we watched and waited as the caterpillars grew...and grew...and grew (and pooped), at a rate of about 1/4" a day! In 8 days they had grown from 1/2" long to 2", and began to make their way to the top of the cup, where they attached themselves and hung upside down in a "J" shape for about 24 hours while the chrysalis formed under their skin, which they then molted one last time. After letting the last chrysalis harden for 2 days, the cloth they were attached to was transferred to and pinned inside the butterfly cage.

Painted Lady pupae in chysalides

Then, it was time for more watching and waiting. After about 7-8 days, the first butterfly emerged early one morning and was waiting to greet my coworkers when they came in. Most of the rest emerged the next day (when the library was closed for a holiday), and the final two the following day. 

Painted Lady Butterfly

Out of 12 caterpillars, we had 10 healthy butterflies. One caterpillar had been unable to attach to the lid and pupated in the bottom of the cup, and did not survive. Another butterfly that did survive and emerge had to be euthanized because its head/face did not develop normally; it had one eye that probably wasn't functional, no antenna, and no proboscis, so would have slowly starved to death.

Feeding Painted Lady Butterflies

I feed them sugar water, orange Gatorade, and mashed fresh fruit to give them variety, putting the liquids in a bottle with a wick or in a small dish of saturated cotton balls. I decided to keep them for a week, in order to time their release with the exact anniversary of the release of The Very Hungry Caterpillar on June 3rd, which I advertised with flyers in the department. Much to my surprise, they began mating right away and laid eggs prior to the release, so if I were to do it again, I would plan on releasing after 3-5 days. 

Painted Lady Butterfly eggs

I had also planned a whole social media component, announcing the arrival of the caterpillars and inviting people to meet them at the special storytime, posting updates and videos, and hopefully catching an emerging butterfly on video, but unfortunately due to bad timing and too much bureaucratic confusion it never happened [our social media person and programming manager both left in May, right before summer reading, so marketing was a hot mess and only high priority summer reading programs were making it onto the Facebook page]. That was very disappointing and frustrating to me, as I felt it was a huge missed opportunity to engage the public on social media.

Another frustration was that out of 12 caterpillars, not only did *I* not witness a single one during the final molt to reveal the chrysalis nor emerge as butterflies, no one else did either. Every single one of them did it after hours when no one was around! I was so disappointed!

Some of the the things I learned during this project:
  • Inside the chrysalis the caterpillar basically liquefies, except for a few highly organized clusters of cells that use the resulting "primordial caterpillar soup" to grow the new butterfly body. 
  • The chrysalis has gold metallic spots.
  • When the butterfly first emerges, its proboscis is in two separate grooved halves, which it has to rub together until they "zip" together and interlock, forming the drinking channel. Click here for a graphic.
  • Caterpillars and butterflies may be shy about revealing and emerging from the chrysalis, but they have no problem mating while people are around!
  • They begin mating almost right away, and though they generally try to wait until they find a suitable host plant on which to lay their eggs, they will lay them inside the cage as soon as 2 days after mating. 
  • The females typically die after they have laid all their eggs (we did have one butterfly die before being released; another reason I would release earlier in the future).
  • People are really bad about poking at the chrysalides and more stern signage was necessary.

This was a really fun and interesting project, and while I must confess I did it as much for me as the public, people really seemed to enjoy it and find it interesting. I had 30-40 people attend the release, and that was without it being listed on the calendar or any advertising other than a flyer posted next to the cage. I had hoped to get the butterflies to sit on the kids' hands for a minute before taking off, but even with the temptation of sugar water, they were too eager to soar, and immediately headed skyward, though one did briefly make a pit stop in one girls' hair. It was less than 30 days from the arrival of the caterpillars to the release of the adult butterflies!

I took way more photos and video over the course of the project than could be included in this post, including some really cool up-close pictures of the eyes, proboscis, scales, and eggs taken with a macro lens attachment, so I put them together in the following video:

Now I'm in the process of planting a butterfly garden at home that I hope will attract some Monarchs and Swallowtails to lay eggs! They are even more spectacular butterflies, and much more attractive caterpillars, than the Painted Ladies. One of my co-workers and I are also hoping to start a butterfly garden at the library, but that will have to wait until after summer reading!

Update: I took the eggs that were laid prior to release home to raise, and four days after being laid, they began hatching into teeny, tiny caterpillars, 1-2 mm long, barely visible to the naked eye (luckily I have a macro lens). The eggs started out blue, then turned black as the caterpillar grew and was close to hatching, then clear egg shells were left behind. I was even able to catch a few hatching on video!


  1. We just did that too, it was awesome! It wasn't tied to a particular program, but we promoted it at all the storytimes and science programs, and then we released 27 painted ladies last Friday! Worms are next, for in-library composting!

    1. Thanks for stopping by! I'd love to hear more about how you are doing the worms & composting! I think that would be a big hit here, too.

      Since I didn't release my butterflies quite soon enough, I now have about 100 teeny tiny caterpillars at home! I'm going to keep some until they become butterflies, but once they get a little bigger I'll have to release the rest of the caterpillars once I find some appropriate host plants outside as the lab-created food is really expensive!

  2. Hello, and thank you for posting all of your findings! We are planning to do this in April 2024. Looking at and item # 144084, it only comes with 5 larvae. Did you order two? Thanks again.

    1. I got item #144012, which is a complete kit with cage and 2 cups with 5 larvae each.