Or Epilobium?
Neat!
Seen on the Lost Palms Oasis Trail
Observed at Canyon Campground, Yellowstone National Park.
White-lined Sphinx Moth caterpillar feeding on a host plant, Brown-eyed Evening Primrose.
3-25-2016: Many caterpillars on and along a section of the Bajada Nature Trail. Half crawling quickly despite the wind blowing them!
I have short video. Can you accept video?