Growing a Bumper Crop of Butterflies

By Mike Weilbacher, Executive Director

I love it when a plan works: walking up the back steps at my home this week, I glanced at the large pots where we keep our kitchen garden. What caught my eye was a bump on the end of a sprig of dill:  a hunchbacked but handsomely striped insect, the unmistakable caterpillar of the black swallowtail, one of our largest, most striking butterflies.

But wait!  A smaller lump below the caterpillar on another leaf was actually a second one.  Then I spotted a third.  Wait, there are six. No ten.  Omigosh: I am the proud father of 13 bouncing baby swallowtails, crawling up and down—and devouring!—my dill.

When black swallowtail caterpillars are first hatched, very small and very vulnerable to hungry birds, they are not striped, but are camouflaged to resemble a bird dropping, black with a saddle-shaped light splotch in the middle. There are a lot of things birds eat (like caterpillars), but they will never touch excrement, so if your kid looks like crap, well, you get the idea.  After a few molts, it’ll put on the familiar striped suit of the bigger one I saw first.

While my dill was being reduced to leafless skeletons, I was elated.  For that was the plan:  we get the basil, rosemary and thyme.  Caterpillars get the dill.

And I am growing a bumper crop of butterflies.

An adult black swallowtail

Butterflies are exquisite botanists, the female laying its eggs only on the plants her babies eat, essentially placing their children atop their dinner plates.  So monarchs only lay eggs on milkweeds, tiger swallowtails on trees like wild cherry and tulip poplars, painted ladies on hollyhocks and pearly everlasting…

…And black swallowtails on dill, fennel, parsley, and wild carrots.

So I hustled out to buy new dill, which they have already moved over onto, and will soon be transforming into butterflies.

Grow some dill yourself, and when you see that caterpillar devouring your plant, don’t kill it: buy it more dill.  And grow butterflies!

Mike Weilbacher directs the Schuylkill Center for Environmental Education.  Email him at and follow him on Twitter @sceemike.