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Limenitis archippus
Bright orange and black with tiny white dots at the margins of the wings.
It was fluttering around a small garden planted by students in a small courtyard behind an art building. It was getting confused by the reflections of the sky in the glass of the large art building.
Nice find! You have been tricked by a trickster! The Viceroy is an excellent example of mimicry. They look like the distasteful Monarch, deterring would-be predators. An easy way to tell them apart the line across the hind wing. Monarchs do not have this. See the image here:
http://bugguide.net/node/view/43528