Giant Swallowtail Caterpillars in MN
I was deadheading the Dictamnus (gasplant) in my fragrance garden last week when I found two really ugly looking things eating the leaves. They were so homely that at first I thought it was mulberry bird poop, which is not an uncommon sight in my gardens. After closer inspection, I discovered that the bird poop had legs so I knew it was alive. The two wormy things did not look like the caterpillars I’m used to here in Minnesota and I was tempted to just throw them into the basket with the spent flowers I had just cut off the gasplant and let them fend for themselves in the brush pile. I thought better of it though and left them there until I could do a little research indoors.
Giant swallowtail caterpillar on gasplant (Dictamnus)
The first thing I did when I got inside was a Google search for caterpillars on gasplant. Bingo! Right off the bat I came up with Dictamnus as a host plant for giant swallowtail larvae. I immediately got out the excellent my friend Nancy had gotten me for my birthday and looked up the giant swallowtail caterpillar. Bingo again! Just to make sure, I looked them up in the National Audubon Society and it still looked like they were giant swallowtail larvae, but there was a problem. I had recently read a by Jeffrey Hahn, U of MN Extension Entomologist, on giant swallowtails in Minnesota and he stated in the article that giant swallowtail have been seen recently in our neck of the woods, but that they do not reproduce in MN because we don’t have their citrus larval host plants.
Very disappointing; however, I decided to go to the man himself and sent Mr. Hahn an email message and photos of the caterpillars. Here is his reply:
Yes, that is a giant swallowtail larva. It is true that the larvae will [also] feed on prickly ash which is part of the citrus family. I was basing my statement that they don’t overwinter on information that Dr. Susan Weller provided me. After my article, I have received a number of reports from people who said they regularly see the adults. You are the first to say that you have seen the caterpillars. I need to get a clarification from Susan on this. It could be that they can mate, lay eggs, even produce larvae but perhaps they just are unable to survive MN winters. Or maybe they do. I will have to check. Thanks for your report! Jeff
So I’m the first to have reported finding the giant swallowtail caterpillars in our area to the Bug Guru of Minnesota Extension. Whoo-hoo! I will let you know more, when I know more.
Giant swallowtails feeding on Verbena bonariensis in my MN gardens