My name is Michael Reaid, and I am currently a graduate student at FSU. Unfortunately, my field of biochemistry leaves me with little experience in the entomology world. I was recently (August 2005) in Glacier National Park in Northern Montana on a hike when I came across an interesting caterpillar. I am just very curious to find out what it is. I’ve attached three digital pictures (optimized, to save mailbox space, so excuse the graininess) I took of it on the trail before I moved it aside into some vegetation. I would really appreciate an ID, or being sent in the right direction. Thank you very much!
Bill Oehlke’s excellent site lists very few members of the family Sphingidae in Montana, but there are three species in the genus Hyles. This is most definitely one of them. The two likliest are Hyles lineata and Hyles gallii. Both species have similar looking caterpillars with high variability. None matches your specimen exactly. We suspect Hyles lineata, the Striped Morning sphinx or White-Lined Sphinx, to be the liklier candidate. We also suspect a green caterpillar has changed color before pupating.
Correction July 8, 2012:
Today while trying to identify another example of this caterpillar, we discovered that there is now a matching example on The Sphingidae of the Americas website indicating that this is Hyles gallii, the Bedstraw Hawkmoth.