Sunday, November 18, 2012

And you Thought Bird ID was Hard...

A Harlequin Darner-- Or is it??
I was looking through some old photos today when I came across a few shots I had taken of a dragonfly last June. It landed on my leg while I was birding at the Daniel Webster Audubon in Marshfield, MA. I could tell that it was darner, and with the help of the book narrowed the ID down to one of two extremely similar species-- Harlequin Darner or Taper-tailed Darner, the two "pygmy darners" of the East.

I concluded that this bug was probably a harlequin darner based mostly on the fact that they are more common, and I had never seen Taper-tailed before, but I realized that I was pretty much impossible to be certain.

But now I have a new dragonfly book, so I thought I would test it out, and seem if I could clinch the ID one way or another. The book (Dennis Paulson's excellent "Dragonflies and Damselflies of the East) said that Harlequin Darners have more than one bridge crossvein on their wings. It also mentioned that Harlequin Darners often land on people's clothing when they are approached, which offered more circumstantial evidence that this was a Harlequin. However, I wanted to be certain, so, using the appendices in the guide, as well as this blog post about pygmy darner ID, I began to try to puzzle out my dragonfly.

The photo above was the best that I took of it, but it isn't at a good angle, so I used one that showed a better view of the top of the wings:

Now the key field mark is found on the wings, so I zoomed in there a bit:

And a bit more. Still not quite enough:

Once I zoomed in this far, I could finally see the bridge crossveins, and be sure of the ID. There are two veins, so it is indeed a Harlequin Darner, Gomphaeschna Furcillata. 

A bit closer look at the veins in question:

And here are some arrows to help. The inner (left) vein would not be present were this a Taper-tailed Darner.
It's always frustrating to have to leave something unidentified, especially if I have photos, so it was satisfying to finally clinch this identification. It isn't that hard, once you know what to look for. Ok, it is a little difficult, but it's not impossible, and that's a start!

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