Hello TN Gardeners! Need your help identifying these creepy crawleys.

I found these eating away at a butterfly weed last night. Discovered another one a few feet away that they had already stripped. But that seems to be all they are eating. At the moment they are considered pests, but I thought I should check around before the wholesale slaughter began.

They look like they just might sting. Having had an experience with pack-saddles, I don't want to find out.

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As you can see in this picture, they don't stop until it's gone. I'm not worried much as this one had already done it's thing for the year and should come back next year.

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Anyone have any ideas? (BTW, click on the images for larger versions.)