however, for what it's worth, it does "look" like Glover's to me. Cecropia caterpillars at this age usually only have four tubercles rich red (near the front), while this one has six (which is typical of Glover's). The coloring varies some though, but usually it's the degree of orange or yellow in the ones behind that is less constant. Also, just from experience having lived in the area, I'd say that this would be Glover's based on location too. The area west of Fort Collins (including all around Horsetooth and the foothills campus below) is where we used to go to look for the caterpillars and pupae (mostly on the willows), and for adults in spring on the sides of the building under the lights. They were moderately common in the area in the 60's and 70's, but there were no houses then, it was all (except the one building) natural or rural, and nobody in the area had heard of "Open Space" as it is used now, at least not in Fort Collins. I've never seen a Cecropia Moth there (not even over to the east side of Fort Collins for that matter), though I think a few have been recorded from Ft. Collins. The closest I ever found Cecropia Moths myself was the Greeley area. East from Greeley all the way to Nebraska you could find pupae of Cecropia (but not Glover's) on most any clump of Sandbar Willow or wild Plum in winter. They used to be especially common around Wray, and in the Julesburg-Ovid area.

A rule of thumb about hybrids (not always true, but mostly) is that usually interspecific hybrids are rare, and odds are strongly stacked against finding one.

Oh, and to my eyes, the thumbnail referenced here from Denver, looks like Glover's. The one from South Dakota does look a bit weird and "off" - perhaps it is hybrid.

There is a school of thought (perhaps not far from the biological truth) that all Hyalophora represent but one single species, merely with regional variants that tend to blend into one another where they meet. The most sharply defined boundary in the whole genus seems to be where Cecropia meets Glover's & Columbia, and Cecropia seems to be the one that stands most apart from the rest.

I agree - looks kinda like kasloensis...occupies the range expected for gloveri, but given the locality of Larimer Co., Colorado, is it possible this may be a H. cecropia or a cecropia-gloveri introgressant/blend - hence explaining the tubercle coloration!

I know Hyalophora cecropia ranges across the eastern half of Colorado west to the Rockies. Isolates are known to occur at fairly high altitudes (5,000+ ft. a.s.l.) and are sporadic along the eastern slopes of the mountains ("western fringe cecropia populations" are scattered across a large area incl. e. & c. Colorado, e. & se. Wyoming, w. & esp. sw. South Dakota, w. North Dakota, and extreme se. Montana) - some reference for details in range can be be found in Collins, Tuskes and Tuttle.

Just to the north of the area where this image was taken (Larimer Co., CO) ... in se. Wyoming (& sw. SD), can be found some very interesting cecropia moth populations! The 4th and 5th instar larvae of these western fringe Hyalophora cecropia are often very similar in appearance to the caterpillar pictured here.

ref.
central Colorado cecropia blend

sw. South Dakota cecropia (blend?)

Moved from Butterflies and Moths.

H. Kasloensis a self sustaining hybrid of H colombia and euryalis. they have all red tubercles.
i sent the link to an expert hopefully he will have time to take a peek! if its not i guess i will eat my hat.

Columbia Silkmoth - Hyalophora columbia?