Saturday, July 29, 2006

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!


John B. said...

According to Kaufman's butterfly guide, Question Marks have a black dash near the tip of the forewing on the top side, but Commas lack this dash. Both Commas and Question Marks have a series of three black dots together in the middle of the forewing. The Question Mark's black dash is just to the outside of this trio. Your butterfly has it, so I would say Question Mark.

Pamela Martin said...

Thanks, John. I see what you mean--the difference you describe shows up in the specimen photographs at Butterflies of Canada too, which I hadn't noticed.

Through the serendipity caused by having this butterfly in mind, I found one that had been collected by a spider, a Question Mark. I'll be posting some pictures. That doesn't prove one way or the other about the living specimen, but does show that this species has been in the yard.

seamus said...

Question Mark: 4 spots. Eastern Comma: 3 spots. see