Tuesday, May 12, 2015

Searching for Isoperla Perlodids at Buck Mt. Creek

I had high hopes this morning as I drove out to Buck Mt. Creek.  It's Isoperla time in our part of Virginia, and Buck Mt. Creek is rich in this type of stonefly.   But you need to find leaf packs to find Isoperlas, and most of those were washed away in the high water that we had last week.  Nonetheless, I did locate a mixture of leaves and sticks by the side of the stream, where I met with success.  The photos I got are not up to my standards -- the clouds arrived with me -- but we take what we can get.

Perlodid stonefly, Isoperla dicala.  It's one that -- to date -- I've only seen in Buck Mt. Creek and the Rapidan River.   Since I've identified this one before -- on 5/1/1/12 and 4/13/13 -- I won't go into detail.  But, the key patterns are easy to see.

"pale marks anterior to median ocellus sometimes indistinct, sometimes with darker border."  (Steven Beaty, "The Plecoptera of North Carolina," p. 23)  On the nymphs that I found, the pale marks were very distinct, and yes, they did have dark borders.

The other feature to note: "dark longitudinal abdominal stripes with very narrow pale borders." (Beaty, p. 23)  You can see the pale borders in the live photos, but they're easier to see in this microscope view.

In North Carolina, this species is not assigned a tolerance value which means there's not enough data to use.   They were plentiful today in Buck Mt. Creek.


I found only one additional species of Isoperla, the one that I've labeled Isoperla nr. orata.  But the photos I took were not something that I want to post.  Here's a shot from last year so you'll know which nymph I mean.

I've sent Beaty some specimens to see if he has any thoughts about the ID.

Two more pics from today.  The first, a "long-horned" caddisfly larva, Ceraclea maculata.  In the photo, you can see its head peaking out at the top of the case.  I found one two years ago in this very stream in the very same riffle.  For a full discussion of the ID -- and some much better pictures -- please see the entry from 5/6/13.


And the second, a flatheaded mayfly, genus Rhithrogena.  Hope to work on the species ID later on, though species ID of Rhithrogena is still up in the air.


Not the best of days.  With sunlight it would have been fine (and of course the sun came out when I headed home!).  But on Thursday, I'm off to the Rapidan River where I expect to see Isoperla species galore.

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