meeyauw: The Pesky Details

Thursday, August 17, 2023

The Pesky Details

Every photo of mine and Jody's confirmed the misidentification.

Remember these cute August 8 caterpillars when I posted about creatures that camouflage as bird droppings? The first creature I highlighted was the Beautiful Wood-Nymph (Eudryas grata). But it wasn't.

Kathryn got in touch with me last night about a caterpillar she had from her property and could identify to genus but not to species. It was a Eudryas. Without looking closely, I told her it was E. grata, the Beautiful. But she had comparison photos from the Internet and wanted to know how I was sure because she thought it might be a Pearly, E. unio. Now, Kathryn has always had an excellent eye for the small details in insect identification. I remembered how she would keep me honest and see what was in front of us, not what I wanted to see. So I looked up the details.

When I submitted my caterpillar to iNaturalist, the AI said it was E. grata. Jody had named it that, also. And then two other people quickly confirmed it. Without ever looking (but I remember wondering) at the two other Eudryas species caterpillars, I accepted the IDs and moved on. But if Kathryn had doubts, I knew I had to look again.

On Bugguide, there are no photos of the third Eudryas species caterpillar (Eudryas brevipennis), and I could safely ignore that one because it lives west of the Rockies.

There are only two differences between the Beautiful Wood-Nymph caterpillar and the Pearly Wood-Nymph caterpillar: dots on the prolegs (1 dot on the Beautiful and 2 dots on the Pearly on each proleg) and the color of the pro-thoracic shield (orange on the Beautiful and white(ish) on the Pearly), both of which I marked on the photo above. I had to reacquaint myself of the meaning of pro-thoracic and how the heck you find it on a caterpillar, but I did.

Kathryn and I agreed that all the caterpillars that she, Jody, and I had were Pearly and not Beautiful. Which meant I had to update the IDs on iNat, tell Jody, and update my post of August 8.

The moth I posted on August 8 was the Beautiful, and did not belong there with that Pearly caterpillar. Below are my Beautiful moth and Joanne Russo's Pearly moth. The inner brown band is smooth on the Beautiful and scalloped on the Pearly. And that's about it for the difference between the two species. It gets a person to wondering why Nature does this. It must be out of perverse pleasure to making humans nuts.