It was sunny and mid-60's today in Wauwatosa, Wisconsin. I have flower gardens containing native plants mixed in with some other flowering plants. This caterpillar has not moved since I found it this afternoon. It is perched vertically on the stem of the flowering part of a smooth leaf goldenrod( top of the plant). This plant is up against my garage and gets 6-8 hours of sunshine daily. Other plants around it include; cup plant, aster, phlox, purple coneflower, and sweet pea vine. The colors on this caterpillar are very vivid. It is about 2 in long and has a smooth body.
Our house is on a block which is surrounded by a nature area/park , and next-door neighbors who also have native plantings in the yards. We are a suburb next to Milwaukee, Wisconsin.
I have made attempts at finding what type of caterpillar this is but am hitting a wall.
Found caterpillar on stem of a smooth leaf goldenrod plant in my garden.