This beetle looks a lot like the Ellychnia corrusca (winter firefly) I've seen in our yard before before during autumn months, except this one was darker. Thanks for any help confirming or clarifying my ID. P.S. I did not actually find it on the goldenrod (Solidago rugosa). I found it resting on the lip of a bucket of water, picked it up, and placed it on the goldenrod. I did so, because it looked injured, and I've filmed Ellychnia corrusca feeding on goldenrod pollen in the past and thought I might help it out. When I returned several hours later, it did appear to be feeding on the goldenrod.