Unknown caterpillar – Flagstaff, AZ, U.S.A.
I am hopeful that you’ll be able to help me with the caterpillar in the attached photos. These were taken on April 26, 2008 in my yard in Flagstaff, AZ, U.S. Flagstaff is in the mountains of Arizona at an elevation of about 7000 feet (a bit over 2130 meters – I think). After perusing your letters on caterpillars (I am amazed at your knowledge), I am wondering if it is an early instar of a Parnassian species? However, my “Butterflies of Arizona” does not list any Parnassians. And, while the National Audubon “Field Guide to North American Butterflies” does list a few, the descriptions of the caterpillars don’t seem to match. This particular caterpillar appears to be white with black, longitudinal stripes, and yellow spots along the sides. It was on a Penstemon, which is listed (in the Audubon book) as a host plant for the Arachne Checkerspot, but the caterpillar description doesn’t seem to match up. I’m at a bit of a loss … Thank you for a wonderful site, and thank you in advance for any assistance.
Flagstaff, AZ, U.S.A
We have to come clean and say we just don’t know for sure. Based on the absence of most typical pairs of prolegs, we believe this is a Spanworm or Inchworm in the family Geometridae, but we cannot locate a good match on BugGuide.
Update May 25, 2014: Meris paradoxa
Thanks to an identification request we received today, we were able to identify the new request as well as the long unidentified posting from our archives as Meris paradoxa, an Inchworm with no common name.