I don't know what it is, but it looks like one of the dagger moths. It could be a marsh dagger/Simyra insularis, but I can't find a picture of one that matches it exactly. Still, dagger moths are extremely variable within each species.

I know for sure it's not a butterfly! :)

Sherry

My mystery cat has been identified by the folks at BugGuide.net as a Painted Lady, Vanessa cardui. I have raised it in captivity and can confirm the identification. This is a first for me as I am only accustomed to raising American Painted Ladies (Vanessa virginiensis). I had a Eureka! moment when a young friend pointed out that it was probably an escapee from one of the copious mail order butterfly kits.

Congratulations! At least it'll make a beautiful butterfly. I've never seen a painted lady caterpillar, but I should have thought of that one - it did remind me of a red admiral/Vanessa atalanta.

Sherry

Painted Ladies feed on a huge variety of host plants, and it doesn't surprise me that you found them on Comfrey. They usually prefer members of the Aster Family (esp Thistles) and Mallow Family (Malvus, Hollyhocks) as well as a few Legumes.
Note: If you don't like the idea of growing ugly Thistles in your garden, try Globe Thistle. With its handsome silver foliage and attractive purple flowers, it makes a good companion to Hollyhocks Arabian Nights (black flowers) and is also a raging nectar source to a great many pollinators as well. Also drought tolerant.