Great site, I’m hooked! I found this amazing creature in Dauphin Co. PA last week in a remote valley area. It was on a type of “bush” fern surrounded by mountain laurel and many other types of ferns in the forest. I know it’s a Sphinx but which one; Laurel, Wild Cherry, Blinded Sphinx? Speaking of blinded, I’m color blind and could use some help here…
I believe you have the larva of the Apple Sphinx, Sphinx gordius. I looked up many websites to find an image that matched your photo, and finally located this site with an image of a parasitized caterpillar that looks like yours. At first I thought your Sphinx had no caudal horn, then I noticed it behind the leaves. It is very distinctive. Though called the Apple Sphinx, the food plants include are apple (Malus), sweetfern (Myrica), Carolina rose (Rosa carolina), blueberry and huckleberry (Vaccinium), white spruce (Picea glauca), American larch (Larix laricina), and alder (Alnus). As you can see, fern is on the list.