Giant Silkmoth Caterpillar at 8000 feet in Colorado: Glover’s Silkmoth we believe

Subject:  What kind of caterpillar is this? Silkmoth?
Geographic location of the bug:  Basalt, CO 81621
Date: 08/15/2021
Time: 12:25 AM EDT
Your letter to the bugman :  Found this caterpillar while hiking on our property at 8000 ft elevation.
How you want your letter signed:  Joe

Glover’s Silkmoth Caterpillar, we believe

Dear Joe,
This is definitely the Caterpillar of a Giant Silkmoth in the genus Hyalophora, but the species has us puzzled because of the two rows of bright red tubercles.  The Cecropia Moth is not found west of the Continental Divide, and according to the Cecropia Moth description on the Agricultural Science website of Colorado State University:  “The Glover’s silk moth, Hyalophora columbia gloveri, occurs at higher elevations within the region and may be found west of the Continental Divide. … Larvae of the Glover’s silk moth lack the reddish tubercles that are prominent with the cecropia and these are instead colored yellow. Caterpillars primarily feed on leaves of Rhus trilobata, but maple, willow, chokecherry, alder, and wild currant are among the other hosts. Formerly considered a distinct species, the Glover’s silk moth is now classified as a subspecies of the Columbia silk moth, Hyalophora columbia (S.I. Smith).”  Though there are some discrepancies in the description of the caterpillar, our best guess is that this is a Glover’s Silkmoth Caterpillar.  When Daniel returns to Los Angeles next week, he will attempt to contact Bill Oehlke to confirm.  To add to the confusion, there is also inter-species hybridization possible.  This BugGuide discussion on the identification of a Glover’s Silkmoth Caterpillar might interest you.

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