Hindwing has slender tail. Upperside dark purple with wide dark border and orange spots at lower outer edge of each wing. Eggs are laid singly on twigs of the host tree, then hibernate.
Caterpillars eat young leaves in spring.
One flight from June-August. Tree sap, raindrops, probably honeydew from aphids and other insects. Oak scrub and oak woodlands. The official State Butterfly of Colorado. G4 - Apparently secure globally, though it might be quite rare in parts of its range, especially at the periphery.