(BG) Red-Spotted Purple (Limenitis arthemis astyanax) - D&M MD 9/2/11

http://bugguide.net/node/view/38193/bgimage
to tell male and female apart:
http://bugguide.net/node/view/442893

"As for gender, the larger one with more brown would be the female. Also, if you look at the abdomens, the female's has a much fuller shape; this usually helps. The genders in this species can be difficult to tell from a photo though, as they look very similar. Generally also, the female wings are a bit less angular and more full in shape, the females often have more pronounced patterning near the margin of the wings. They behave a bit differently too, with the males more likely to act pugnacious towards other butterflies and to establish territories, while the females more casually fly along the edges of sunny areas looking for places to lay eggs. Both genders will sometimes suck minerals from the ground, and both will occasionally (but not often) come to flowers.

Easiest way to tell them apart is if they are in your hand and you look at the tip of the abdomen, which is shaped differently (the males have a pair of "claspers" there). Sometimes you can see this in a live photo that shows the underside, but most often not; often you can see it in a shot of the underside of a pinned specimen."