Thursday, May 5, 2011

Exhilaration and Frustration: A Day at the Rapidan

As I always do, I found some wonderful insects today at the Rapidan River.  But I was frustrated by two of my nymphs when I got down to the work of genus level identification.  One of the "problem children" -- the Perlodid stonefly pictured above.  It's beautiful, and I was sure I had found Perlodid genus number 6.  But when I keyed it out with my microscope, anatomically, it checks out as an Isoperla.  This looks nothing like the Isoperla that I'm used to seeing (see previous entries).  Still there are many, many species in this wide-ranging genus.  I'll keep working on this one.  But if there's anyone out there who can help pin it down -- to genus and species, or correct me on the genus ID -- please feel free to chime in.  Here's another look.

The other insect that thrilled me was this huge Limnephilid (Northern Case-maker) caddis.  This case is slightly over 1 inch in length.

Very, very cool!  I was hopeful of coming up with the genus ID.  I think it's Pycnopsyche -- but I'm not 100% sure.  As I've noted before, genus ID of Limnephilids is a difficult process, and I don't feel confident that I found the sclerites on the lateral humps that I wanted to find.  I also had problems pulling this one out of its case.  But, I'm determined to work on this some more.  Here's another look at this case-maker when it was on its back in my tray.   You have to admit it -- that is one really neat case.

On to things that I could identify without any problem.   There's no reason to produce photos of all that I saw.  I had a very nice, very big, freeliving caddisfly -- a green one; and there were crane fly larvae in the leaf packs, and netspinners and flatheaded mayflies (all Epeorus) on the bottoms of rocks.  I also found a beautiful common stonefly (Perlid) on a rock, of which I did get a very good picture.  This is genus Acroneuria.

But once again, it was the leaf packs -- well, and some "root balls" that were covered with leaves -- that held most of the mayflies and stoneflies.  They were loaded -- it almost goes without saying -- with spiny crawler mayflies, genus Ephemerella.  Also flopping around in the leaves, some large brushlegged mayflies.  I saw small brushlegged mayflies when I was here in the winter, but clearly, these insects are really starting to grow.

I found two other stonefly families -- in addition to the Perlids and Perlodids that I've already mentioned.  First, there were a lot of Peltoperlids (Roach-like stoneflies) running around -- and they were big!  I'd say they're getting ready to hatch.    And I finally found one whose wing pads were tipped in black (this is the first time I've seen this) -- a sure indication that it's fully mature.

And the other stonefly family here represented was the Chloroperlidae -- the Green stonefly.  And I found a real beauty.

This is genus Sweltsa -- apparently Sweltsa lateralis (see Tom Murray's photo at  This is the first time I've found a Chloroperlid in this stream, and I was a little surprised: I expect to find these only in small, mountain streams.  The Rapidan, where I look for insects, is already a pretty wide stream.  Still, it is clean and cold and running through completely forested land -- the other habitat features this insect prefers.

As I was leaving the Rapidan River, I thought to myself: "With so many wonderful insects in here, why bother going anywhere else?"  But then, I already know the answer to this one: different streams have different insects -- families and genera -- and I don't want to miss out on a chance to see something new.

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