A brown and orange butterfly with angular wings and small tails on the hindwings flutters past. What species is it? In the eastern U.S., it could be one of two species: Eastern Comma (Polygonia comma) or Question Mark (Polygonia interrogationis).
For identifying them, it helps to have a good look at both the upperside and underside of the wings. The uppersides differ only subtly, but they help distinguish the pair from other butterflies with brown and orange markings. On the undersides, there are telltale white markings. A Question Mark has a small curved line with a dot next to it – together they resemble a question mark. An Eastern Comma has a curved white line without the dot – more like a comma.
Fortunately, both Eastern Commas and Question Marks will often land and pump their wings open and closed, making it possible to see both sides.