Black Swallowtail

 Chrysalides are like a box of chocolates, you never know what you might get. (With thanks to Forest Gump.)

This has been the big year for Black Swallowtails.  For us it began when Barb was pulling the flowering tops off of invasive poison hemlock.  She brought them home in a black plastic bag and out crawled a caterpillar.  We put it in a plastic box and it quickly formed the pupa below.

Then she started finding them on our fennel and dill in the gardens at the creek and in Springfield.  She had been raising these plants in our gardens for years without finding them and now they are everywhere!  We have them in all stages now and are seeing the results.  And they aren't always what you expect!

Starting to pupate

Pupating on a chrysalis

One caterpillar even bypassed all the twigs and branches left for it and attached to another chrysalis to pupate.

While Black Swallowtails evolved in North America eating a number of plants in the carrot family that I don't recognize, they have learned to love imported food.  This includes a lot of of our herbs like dill, fennel, caraway and parsley.  They also eat some imports we wish had not made the trip like poison hemlock and its benign cousin Queen Anne's lace.

This is the result we expected, a gorgeous Black Swallowtail.  The various black swallowtails are hard to separate, especially on the wing.  The Black and Spicebush are especially close with two rows of orange spots on the underwing but this side by side comparison may help.

Newly emerged and hanging on fennel.

You won't have any problem separating this unexpected result for another chrysalis.  We were startled one morning to find it in the cage with the newly emerged swallowtail above.  This is a Trogus wasp, a parasitoid that lays its egg on a butterfly caterpillar.  The larva will live in the caterpillar, eating away inside while leaving just enough for the caterpillar to survive and pupate.  It then finishes off its host before emerging.  I suspect it was as surprised as we were to meet that morning.  Meet Trogus pennator.  I knew it looked familiar and finally realized that we had written a blog about Chris Barnhart's finding in 2011.


This Ichneumon wasp specializes in swallowtail butterflies for its eggs.  Lots of the pictures show it with Black Swallowtails but it avoids a look alike Pipevine Swallowtail due to its chemical toxins.  Looking back at the exuvial chrysalis we realized that this wasp had parasitized the larva that Barb found on our hated invasive poison hemlock.  We have to train them next time save the herbs.