There were about 6 of these beetles on St. Johnswort (Hypericum perforatum), a very pretty non-native plant that spreads widely. Beetles in the Genus Chrysolina were introduced to control this plant and must be doing a good job because I certainly don't think it is as common as once upon a time. I am not sure which Chrysolina species this is, whether quadrigemina or hyperici. This one fell off a St. Johnswort plant onto the leaf of a Mullein plant.