I was just walking through a wild area in Seattle with lots of weeds, and came across some strange caterpillars. They are mostly hairless (to the naked eye, anyway), and are striped black over orange with black legs. Can you tell me what they are?
I believe you may have seen the Cinnabar moth caterpillar, Tyria jacobaeae, which was introduced to the United States to control a noxious weed, tansy ragwort (Senecio jacobaea). Here are pictures to compare, and more information:
Wikipedia
Flickr image
Both Washington State’s noxious weed control board and King County Noxious Weeds have information on weed control with Cinnabar caterpillars. (See page 5 of the document). Tansy ragwort is a Class B noxious weed, and control is required in King County.