Friday, October 7, 2011
An Odd Day at the Moormans
I went up Sugar Hollow this morning to one of my "super" tributaries that flows into the Moormans in hopes of finding some Rolled-winged stoneflies. That stop was a bit disappointing -- I'll return to that in a moment.
But on my way back down the Hollow, I noticed a pull-off below the "first bridge" (for those of you who travel this way), and decided to stop and look at new water. In the riffles I found a few flatheaded mayflies crawling around on the rocks, and in the leaf packs, some common stoneflies, genus Acroneuria. I was about to give up and go home when I noticed a lot of old, rotting leaves piled up on the bottom of a pool of slow moving water. What the heck! This is not some place I normally look for insects, but I thought I'd give it a try.
Dragonfly nymphs! Lots of them. And the prize for me was the nymph in the photo at the top of the page since it's one I've never seen before: family, Macromiidae, genus, Macromia, common name -- Cruiser dragonfly. This is close in appearance to Corduliidae dragon flies, and I found a lot of those over the summer in the Rivanna at Crofton (see previous posts). But it has a number of distinguishing features. Let me read from Merritt, Cummins, and Berg (Aquatic Insects of North America, p. 246).
"Head with a prominent frontal horn between bases of antennae; legs very long, the hind femur extending to or beyond the hind margin of abdominal segment 8;...abdomen strongly depressed, almost circular in dorsal view...MACROMIIDAE"
The "prominent frontal horn" -- (actually, it's visible in the live photos)
The very long legs are obvious. And for the hind femurs extending "beyond the hind margin of abdominal segment 8"...
This last photo also shows the feature that make this genus Macromia -- the lateral spines on segment 9 are shorter than the "abdominal appendages" (see Peckarsky, Freshwater Macroinvertebrates, p.51).
So, a new insect to add to our list: the dragonfly Macromiidae, genus Macromia.
But there were other dragonfly nymphs in those clumpy leaves as well: I found another "Darner dragonfly" (Aeshnidae), and another genus Hagenius "Gomphid" (Club tailed dragonfly).
And now for my first stop of the morning, that wonderful little stream in which I found so many spectacular insects in the winter and spring. It was virtually dry -- just barely running. All of the rain that we've had in the Charlottesville area in the last couple of months has simply skipped over the eastern base of the Blue Ridge. It's a very sad situation.
Now, despite the low water conditions, I did find insects. In fact in the few leaf packs that I could find, there were lots of Roach-like stoneflies, young ones still growing up, and lots of small Giant stoneflies.
I saw no reason to take photos of these. But I did find something that was too pretty to omit from today's photo album.
A beautiful crayfish! He, too, was hunting for food in a pile of rotting leaves in a pool of slow water.
All in all, a very odd day: not at all what I expected. But I did learn of a new place to look for insects when I'm out on the stream.