Saturday, May 28, 2016

Common stoneflies -- uncommonly colorful: Perlesta at Buck Mt. Creek

Just back from Buck Mt. Creek where the water remains high and slightly off-color.  Just need to stick to the small mountain streams for a couple more weeks.  But, no problem finding insects: my tray was loaded with tiny, small minnow mayflies.

And, no surprise I found some Perlestas (common stonefly, Perlidae).  They really are "common" in our streams at this time of year, and as a genus Perlesta is fairly tolerant for a stone -- TV of 2.9.  Clearly, when more work is done, we'll find that the TV will vary with species.  As I noted a few days ago, we find them in our very small headwater streams, in medium waters like Buck Mt. Creek and the Doyles, and in our "large" river, the Rivanna.

I took photos of two nymphs this morning, the two quite different in color.



When I look back at Perlesta photos I've taken in previous years, one of the striking things is the different colors of the nymphs that I've have seen.  Have a look.

What I don't know, of course, is whether these variations are a matter of species, habitat, or maturation (which clearly plays some sort of role).

For genus ID, I turn to Steve Beaty's "The Plecoptera of North Carolina," p. 19: "Nymphs 8-12 mm; setal row on occiput complete, sinuate, and with irregular gaps; abdomen with numerous short, stout intercalary setae, often with pigmented bases giving abdomen a speckled appearance; anal gills present; body covered with fine, dark clothing hairs."

No need for microscope photos to discern these critical features.  For the occipital setal row, the intercalary setae (speckled appearance), and the anal gills

and for the dark clothing hairs.

Most common month to find Perlestas out there -- June.

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