With its wings closed this butterfly is about a half-inch (1cm) across. Its small size explains why it is relatively unknown (by me at least) despite being one of the most common and widespread butterflies in the northern hemisphere. Our field guides call it the "American copper," but "common copper" might be more accurate. Lycaena phlaeas.
My neighbor is a dogwalker, and was passing by with a golden named Murray so I brought Turkey Bryce out to meet him. They immediately engaged in a spirited game of biteyface.