Female Williamson's Emerald at Phelps Rd Ravine, Brantford

[Bill Lamond]

Hello,

Today (17 June 2022) I found myself without a net when I came upon a freshly emerged female Somatochlora. I was also without a decent camera. At any rate the individual was hanging from an open branch about 8' up. I could easily study it with binoculars. For a moment I wondered if it might be a Plain's Emerald as the thoracic stripes were so prominent. I quickly discounted that when I noted how long the cerci were. With the shape of the ovipositor, it left only three possible species; Mocha, Clamp-tipped and Williamson's. Mocha was easily ruled out because of the strong thoracic pattern which I thought should rule out Williamson's as well. So I deduced it was a Clamp-tipped and tried to take some photos with my cell phone and my point-and-shoot. It was impossible with these two cameras to get decent in-focus photos. Nonetheless, here they are.

After a time I noticed how prominent the abdominal spots were. This is not a feature of Clamp-tipped but a feature of Williamson's. The thoracic stripes seem better suited for Clamp-tipped but in a fresh Williamson's (this individual must have just emerged today) these thoracic stripes can be prominent but will fade quickly with aging. I don't find the shape of the ovipositor of much help in distinguishing these two species although some people might. 

So I think this is a Williamson's largely based on the abdominal spots. I do note that there is a large yellow spot on the side of S2 which is a good feature for Clamp-tipped and I wonder if an extremely fresh Clamp-tipped might possess abdominal spots which could disappear in a day or two?

It is interesting to think that even if I had a net and was able to catch it, or if I had gotten good photos, I'm not sure if it would have mattered. I don't think having the individual in the hand would have helped me to be certain of the ID.

I have to say that based on my Somatochora experience over the years, that separating female Williamson's and Clamp-tipped is an underrated ID challenge at times.

I invite any comments on the ID of this emerald.

thanks,

Bill