Question Mark or Comma?

Not a question that comes up a lot--usually it's pretty clear when a question mark is required, even if I slip up on the blog sometimes. Found a butterfly this morning clinging onto an iron lamp in the garden. Grabbed the best picture I could (sometimes a subject just won't stay still), but didn't get the picture I need as it turns out. I have a couple of baby guides to butterflies and moths. One didn't have this butterfly at all. The other (Peterson First Guides: Butterflies and Moths) led me to identify it as a Question Mark (Polygonia interrogationis), so called because of a mark on the underside of its hindwing.


With my success in identifying the Milbert's tortoiseshell, and now this, I felt like I was on a roll. Then Googling around on the internet I discovered that there are two very similar butterflies, Question Mark and Eastern Comma (Polygonia comma). The best distinguishing feature between them is that little mark on the underside of the hind wing. (See here for Bev of Burning Silo's excellent photo showing the underside of an Eastern Comma's wing.) Oh sure, the Question Mark is bigger, and the markings on the top side of the wings are subtly different. But I only know this butterfly was an impressive size not whether it falls to one side or the other of the given ranges: 45-68 mm for the Question Mark, 37-56 for the Eastern Comma. The other distinguishing feature is "the long, violet-edged hindwing tails" of the Question Mark. That sounds more helpful, but my butterfly seems to have a bit more tail than the Comma at Butterflies of Canada, and less than the Question Mark there. Their Comma is missing the pale edging of the Question Mark, and mine has it--but the text warns that this may be seen in a Comma.

Also according to the species page for the Question Mark at Butterflies of Canada: "The summer generation (form "umbrosa") is darker; the hindwing upperside is almost black, and the underside is more heavily marked than in the overwintering generation." Which is certainly true of this specimen. And of course, it's also true of the Comma.

So this is definitely a summer generation Polygonia, possible comma, possible interrogationis. I think it's probably Polygonia comma....

Just like learning to identify birds, once you start to look at the butterflies, there's so much to see. And there's so much to learn--I learn something more every time I grapple with an identification. I'll know this butterfly (i.e., these butterflies) if I see it again, and know I've got to get a look at the underside of the hind wings!