We have a large stack of old Ranger Rick magazines stored in a tub downstairs. They have been sitting there for probably a year or so, passed on from my own childhood, just waiting to be read again.
This summer the time was right -- my 6 & 8 year old kids found them, and they devoured them. I was hearing all sorts of nature facts and answering all sorts of questions about animals and the environment for weeks as they hunkered down on the couch with their piles of magazines next to them.
So when we found a couple caterpillars on our parsley plants in the garden, my 8 year old knew just what to do:
"I know how we can build a caterpillar house! I read about it in Ranger Rick!"
This was, apparently, much more sophisticated than my suggestion of just sticking them in a glass jar with holes in the lid. Of course, it involved me doing all of the cardboard cutting and wielding of plastic saran wrap, but it brought a lot of excitement and happiness to the younger portion of the household. And they didn't even mind that we used a tacky freezer pop box or that my taping job was far from perfect.
Inside of the box (with the saran wrap "windows") we placed a glass jar filled with water, covered with a paper towel, through which we punched a dill stem for the caterpillars to feed on. The cardboard frame also had holes punched in the top ('cause caterpillars are sure used to having air...), and Margaret stuck an appropriately sized stick through the plastic wrap for them to hang from when they were ready to form their chrysalis.
We changed out the dill stem every couple days so that they had fresh food, and they were ravenous little guys. They were, by the way, "Parsley Worms".... a.k.a. Black Swallowtail caterpillars - some of my favorite butterflies. I don't mind planting a little extra dill or parsley so we can encourage them hanging around.
One thing I should have remembered from past dealings with caterpillars, is that very hungry caterpillars also produce an enormous quantity of frass (a.k.a caterpillar poo). So if you copy this handy little project, make sure you put something under the cardboard box frame to catch all those droppings right from the start! (Newspaper or paper towels work well.) Especially right before they create their chrysalis, when they excrete a dime sized bit of waste in preparation for their transformation.
Also beware that these little guys like to roam just before chrysalis time, searching for that perfect spot to camp out. This caterpillar house works well to keep their wanderings in check, in theory, except that ours had one bottom edge that was just saran wrap without cardboard, so they snuck under that once or twice and we had a couple exciting caterpillar hunts. Fortunately the renegades were found every time.
There is a great blog post here about raising black swallowtail caterpillars.
Our favorite part about these caterpillars was their defensive response of popping out their osmeterium - the orange two-pronged "horns" that emerge from behind their head when they get scared. When I allowed the kids to touch them they would rear up, pop out their osmeterium and look as ferocious as one inch little striped caterpillars can look. The kids thought it was the most hysterical thing they'd ever seen.
After a week or two of feeding caterpillars they formed their chrysalises, and in another two weeks they hatched out!
The kids were pretty sad how fast the newly hatched butterfly flew off without a backward glance - they were excited to be released outside! But for the next few days we had a few close encounters with a black swallowtail butterfly as we worked outside, and the kids were convinced that it was "their" butterfly wanting to hang out with them.
All in all a successful and easy summer project that I would highly recommend.
I even briefly thought about building a nicer, more permanent caterpillar house - with the same general design as this one, but out of wood and some sort of light mesh or netting. ...Not that I didn't love the bright blue freezer pop box and masking tape look..... But I'll update in the future if I ever follow through with that idea.