Raising Caterpillars to Butterflies

Raising caterpillars to butterflies is a great activity for families, especially now as we parents try to figure out remote learning, inventing educational projects for our kids.

We've raised about 6 caterpillars this summer, all of them cabbage whites until now, and it's become a fun activity that my daughter and I do together.  Here's our routine.  (Feel free, of course, to adapt to your family's rhythms!)

Step one:  Caterpillar hunting.

We started our caterpillar / butterfly journey with the cabbage whites that lay their eggs on (and can destroy) brassicas.  We watched as the butterflies laid eggs that hatched on our broccoli and kale seedlings.  Then, instead of either killing the caterpillars or leaving them to eat the seedlings to the ground, we brought them indoors and fed them from our more mature kale plants until they turned into butterflies.

At the same time, in a much longer term project, I started native California narrowleaf milkweed from seed last year.  The plants are finally big enough to attract Monarchs to lay their eggs.  I found the first caterpillar a couple months ago, and showed my daughter.  Ever since then, she checks the milkweed plants regularly, as part of her routine in the garden.  Now she always finds the Monarch caterpillars first!  It's a fun, low-stress activity that gets us looking closely at details in the garden, watching for caterpillars, and tracking them as they grow.

I should mention here that Monarchs in particular are endangered and should mostly be left alone, and mostly we do.  The Xerces society, one of the most trusted insect conservation organizations, recommends against captive breeding and raising of Monarchs.  But they say it's ok to raise one or two, especially as part of teaching children about Monarchs and conservation.  So we decided to bring the one pictured below into our kitchen, and raise it like the cabbage whites.

Step 2:  Create a caterpillar habitat

The Joyful butterfly has a nice, detailed description of everything you need to keep your caterpillars happy indoors.  The things to remember are:

1. Feed the caterpillar the same plant you find it on.  Monarchs, for example, can only eat milkweed.  Cabbage whites only eat brassicas.  If you don't know what kind of caterpillar / butterfly it is, just keep feeding it from the plant it was on when you found it.
2. Keep it safe from drowning.  If you want to keep a cutting of the host plant in water, make sure the water is covered by a lid with a small hole in it, or perhaps some foil.  You can also just add fresh leaves to the habitat every day.
3. Caterpillars don't need water.  They get all the moisture they need from fresh leaves.
4. Clean out the poop!  Caterpillars poop a LOT! And their habitat can get unhealthily dirty.  Periodically, remove the caterpillar gently, clear out the frass (the name for caterpillar poop), and put it back with fresh food.
5. Keep it ventilated.  You can keep caterpillars in jars, as long as there are air holes in the lid, or you can use mesh or fabric to cover the top like we do.  You can also keep caterpillars in the open, just on a branch of the host plant on a table.  But beware that caterpillars in the open may wander off.
6. Keep it out of direct sun so the caterpillars don't overheat.

Step 3: Watch your caterpillar turn into a butterfly.

After a week or so of eating, your caterpillar will look for a spot to pupate.  It will attach itself to a branch or the underside of a horizontal surface, create a chrysalis, and spend about another week transforming.  

While the caterpillar attaches and builds the chrysalis, it's quite vulnerable.  Take care not to shake or move the habitat for the first few days of pupating.  Once the chrysalis has fully formed, you can gently move it to a bigger habitat if it will need more space when it hatches.

The butterfly emerges slowly and then spends a couple hours drying its wings before it's ready to fly.  Make sure that whatever habitat you've chosen has enough space for the butterfly to stretch its wings before you release it, and a big enough opening that it won't damage its wings as it flies away.