I checked the EXIF data attached to the image, and it shows 4/29/2007 as the date on the camera's internal clock when the image was taken. I suppose one could arrive at 14 mm by reading the inches side of the ruler as if it were the mm side.

Thanks, Chuck. I did some additional research as well, and I have good news and bad news. The good news is that the emergence of the transcontinental species Pteronarcys dorsata varies widely from region to region. In parts of the Midwest they are reported to emerge in April and May, which would correspond to the camera data. The other Midwestern species, Pteronarcys pictetii, is said to emerge in May and June.

In a comment on another photo in this group, Ictodd identified this as P. pictetii. I'm not sure how the species determination was made, but I did confirm the genus in my comment on that page. I would suggest moving this to genus for now, even though the emergence dates might seem to suggest dorsata.

Now for the bad news. In checking around, I discovered that another bug ID site had used this specimen to misidentify multiple photos sent to them. About half way down this page you'll notice that they have correct IDs on later specimens of the same genus, but never seem to have realized that they were, in fact, the same genus. The result is a very confusing.

Until I saw this, I never really considered misidentification/misplacement snowballing onto other sites, I was just concerned about it happening here. In our information age, snowballs don't just roll downhill anymore--they fly through the ether of cyberspace! :)