In spite of the name, there is strong evidence that the "American" Copper was in fact introduced to America long ago, perhaps in hay shipments from Europe. In the Old World it is known as the Little Copper or Eurasian Small Copper, and the two "species" are quite similar. Also, the American Copper's host plants (what the caterpillars feed on) are Eurasian species not native here, primarily sheep sorrel (Rumex acetosella) and curly dock (R. crispus). Even if the little butterfly was an unintentional import, it is an attractive and charismatic little butterfly and I'm not aware of any issues that it has caused.