Moved from Papilio.

Moved from ID Request.

however, this does look like P. multicaudata to me. Do you know what the plant is? It looks like perhaps Willow? This one looks about half grown.

The other likely candidate for Golden would be P. rutulus, in which the black ring of the eye spots is usually thicker without the (almost) second inner ring. I think this is a fairly constant difference in older larvae, but am not sure if how to tell the "bird poop" looking younger ones apart.

P. glaucus larvae have a different looking eye spot, and while they might turn up in Golden, they are not common. P. eurymedon rarely comes down out of the mountains (but it isn't far up to where it is common), and it is not as likely that it would be that one either. All four feed on a variety of woody deciduous plants, but P. glaucus has a great fondness for plants in the Lauraceae (but those are rare in Colorado), and I think it is most likely to be on cultivated trees like Prunus, Fraxinus, and I suspect Ulmus. P. multicaudata favors Fraxinus, with Chokecherry and native Salix used a lot too. P. rutulus likes Salix and Populus tremuloides best, but will often be found on Chokecherry. P. eurymedon is usually associated with Aspen in the moist cool areas in the mountains in Colorado, but feeds mostly on Rhamnaceae in other regions.

all the Papilios apart