Wednesday, July 18, 2012

Back to the Rivanna: Lots of Heterocloeon curiosum

Another day to beat the heat as it again climbs towards one hundred degrees.  Tough working conditions, with sweat pooling up in my viewfinder and the humidity fogging my lens.  But I hate to miss out on seeing more insects.

Still nothing dramatically new in the Rivanna: I see a lot of silted up common stoneflies, and a lot of silted up flatheaded mayflies, and a lot of common netspinners -- it's their time of year -- and the occasional hellgrammite.  Oh, yes, and the odd Giant stonefly here and there.  I'm always mystified to find them in this kind of water, but they're here nonetheless.

So, my focus becomes the summer small minnow mayflies, the summer spiny crawlers, and -- when I see them, which ought to be soon -- the "little stout crawler" mayflies: "tricos" to fly fishermen.  The main small minnow mayfly I'm finding in the Rivanna at Darden Towe Park continues to be the Heterocloeon curiosum.  And I always see, or so it seems, more females than males.  This morning, one in particular, posed for some very nice photos.

When she turned on her back, I got a picture that helps us ID these nymphs to the level of species.  In this photo, you can clearly see the spots of pigment in the center of each of the gills and the "procoxal" gills at the base of the front legs, both defining characteristics of H. curiosum.

I had only one male in the collection today, and he was not cooperative when it came to my taking photos.  This is the best I could (but note the big eyes).  The male nymphs are undeniably smaller than the females.

I also found several Serratella spiny crawlers -- Serratella serratoides.  I had trouble getting them to pose on their own: they love to cling to vegetation if there's some in the tray.

The dark brown color and the "spiky" tails -- which are banded -- always give this one away.

Finally, I found another Leptocerid, a long-horned case-maker caddis.  I'm seeing a lot of these larvae this year, having now found them at three sites on the Rivanna: Darden Towe, Milton, and Crofton.


We'll be making a quick trip up to PA this weekend where I hope to get into some smaller streams in the mountains.

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