Wednesday, February 16, 2011

Stream Report: North Fork of the Moormans

I did not find that a whole lot had changed in the North Fork since my visit on 1/3 of this year (see previous entry).   But I did find a lot of Lepidostomatid case-makers -- as in the photo above -- all of them in the leaf packs.  (I picked up a dozen in the first leaf pack that I sorted through.)

As expected, I saw a lot of Epeorus flatheaded mayflies.  When I turned over some rocks, I saw at least a dozen scamper in every which direction.  (Flatheaded mayflies, by the way, hardly ever (if ever?) move directly forward or backward; they sidle off at an angle, diagonally across the rock -- gives them away every time!)  These two pictures will show that the nymphs today were quite a bit bigger than those I found at the start of the year.

It's worth stressing for readers new to sampling that these are MAYFLIES, not STONEFLIES!  Too often we rely on the "general" rule that "two tails" = a stonefly; "three tails" = a mayfly.  True, all stoneflies have two tails, but so too do a couple of mayflies, at least several genera of mayflies.  As noted in the last entry, there are three small minnow genera that have only two tails; the same is true for this flatheaded genus -- Epeorus.  With this nymph, the abdominal gills should tell you that it's a mayfly, and the flat head, with eyes that are totally dorsal (on top of its head), indicates that it's a flathead (family: Heptageniidae).

Two other items of interest.  One is that I found a very small Perlodid stonefly that I'm quite sure is a baby Isoperla.  The features we use for identification make it either Clioperla or Isoperla, and since Clioperlas by now are quite large and Isoperlas are just now appearing, I think this conclusion is sound.
In the photo below, I've placed it next to a mature Perlodid so you can see the difference in size.

Isoperla Perlodids, again, are normally mature in April and May.

The final note is that there are now large colonies of large black flies in the stream -- but I'm finding that to be true almost everywhere that I go.  In the photo below, I've tried to show you what this would look like as you look at a rock down through the water.  I've drawn arrows to all of the clusters and rows of these ugly black buggers.

If I were out sampling and reached down to rub some rocks, I'd leave this one alone and move on!
Oh, I know, that's not the advice you'll be given -- but there are hundreds, maybe thousands, of black fly larvae on this rock.  Do you want to sit and pick them all off of your net?!  (I've done it; it's not fun!)

Oh!  Almost forgot.  The stream was loaded with large winter stoneflies, genus Strophopteryx; I didn't see any small winters; and I only saw two Taeniopteryx large winter stones.  Still, one of them was kind enough to lie on its back and let me get this good shot of its "coxal gills," the large, white "telescoping" gills at the base of each leg.

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