"What a thousand acres of Silphiums looked like when they tickled the bellies of the buffalo is a question never again to be answered, and perhaps not even asked." -Aldo Leopold
Walnut Sphinx
Amorpha juglandis fam. Sphingidae (Hodges#7827)
Host plant: Found on hickory (Carya sp.)
Date found: 6, 13, September, 2025
Location found: Babler State Park, Tyson Research Center, St. Louis County, MO
Notes: This is the only species of this genus in North America.
I believe this is the last I have to share from this year’s caterpillar season. Overall, I think this was a successful season and I had a lot of fun finding some cool species. I still have tons to learn and species to find. I’m hoping to continue this next year and hopefully get going on early season hunting. This is quite difficult because the spring and early summer are great for things like birds and plants as well. I need more Saturdays!
I’ll finish up with this fantastic late season walnut sphinx caterpillar (Amorpha juglandis) that I found at Onondaga Cave State Park in late September. I finally noticed that this genus name, Amorpha, is shared with one of my favorite groups of plants, the false indigos, like Amorpha fruticosa. I looked this up and Amorpha comes from Greek for “shapeless” or “deformed.” This genus of plants received this name due to their having only one petal on their flowers, unlike the rest of the Fabaceae.
Amorpha juglandis has been in a few other genera and now is placed in it’s own monotypic genus. I have not been able to find out which particular characteristic provides the “deformed” nature for the Amorpha epithet. If you know this, I’d be grateful to learn this.
For tonight’s caterpillar, I am featuring the Sphingidae family member, Amorpha juglandis – the walnut sphinx moth. This is the only species in the monotypic genus, Amorpha, a name that is shared with a plant genus that holds our leadplant (Amorpha canescens) and false indigo bush (A. fruticosa). This name comes from the Greek – amorphos- meaning formless or mishappen. This describes the lack of wing and keel petals of the corolla of these beans. For the moth, I am not completely certain, but it may have to do with the unique shape and placement of the rear wings when this moth is at rest. This species is very easily identified in both larval and adult forms.
First up are a couple of early instar brood mates that I found on the same walnut tree in mid-July at Kaintuck Hollow in Phelps County, MO.
Next up is an older cat found at Schoolcraft Prairie in Washington County, MO in mid-August. Caterpillars of this species at this stage are infamous for its defensive displays when harassed, including emitting a high-pitched squeak, thrashing and biting. Unfortunately, this one was pretty chill, so I could not show this off to the folks I was with.
Finally, on the same night we photographed the caterpillar pictured immediately above, an adult male moth was attracted to our blacklight setup. This was my first looks at the adult form of this species.
A Thousand Acres of Silphiums 