Subject: White caterpillar with black stripes, black dots and yellow dots
Location: Northern Arizona
May 25, 2014 10:00 am
I found several of these caterpillars in a pinstemon plant in Flagstaff Arizona.
This is an Inchworm or Spanworm in the family Geometridae, and the common name for the caterpillar is because of the number of prolegs, two pairs, resulting in a manner of locomotion where the caterpillar stretches out with is true legs and then moves the entire hind section in one step, inching along and causing the body to loop in the manner illustrated in one of your images. Interestingly, our first attempt at a species identification, thank to your inclusion of the food plant Penstemon in your description, produced a matching image from our archive that has been unidentified to the species level since April 2008. We hope to remedy that identification plus your identification today. Without too much trouble, we located Meris paradoxa on BugGuide. The host plant is listed as snapdragon, and Penstemon is in the snapdragon family Plantaginaceae.
Thank you so much for solving the mystery. I looked all over the internet for a couple of days before I asked for your assistance. Wow, such a colorful caterpillar turns into such a drab moth.