Thursday, March 26, 2015

Buck Mt. Creek yields the Nemourid stonefly, Prostoia completa (Central Forestfly)

This morning it was not in my plans to go to a stream.  But about 10:00 am the sun popped out, so I was off to Buck Mt. Creek.  And I was rewarded.

This is a small stonefly that I've only seen a few times -- once before at Buck Mt. Creek (3/1/11) and a few years ago at the Rapidan River (downstream from the section I normally visit).  Nemourid stonefly (Forestfly), Prostoia completa, for which the common name is "Central Forestfly."

The Prostoia nymphs are very small -- 5-6 mm when they're mature -- and I had one that was 5 and one that was 6.  The pronotum provides one of the keys to genus ID: "rounded pronotum with no marginal fringe (or of very small spines)."  (Beaty, "The Plecoptera of North Carolina," p. 4)  We can see the those small spines in this picture,

and we can also see a key feature in the species ID: "white spots on head covering both sides of Y-shaped ecdysial line."  (Brigham, Brigham, and Gnilka, Aquatic Insects of Oligochaetes of North and South Carolina," p. 5.20)  No question about it.  Actually that feature shows up quite well in the live shots.

Nice find, and I'm pleased that my photos turned out.  But, I have to admit that the photos I took of this nymph on 3/1/11 were actually better!


The water was high, and as you can probably tell, the leave packs were quite silted up (= dirty nymphs), so I didn't search for a lot having found three P. completas without looking real hard.  But I did find a gorgeous, fully mature Helopicus subvarians Perlodid.

18 mm -- that's a pretty big stonefly!


Sunshine coming for Sunday.  I'll be spending the day in Sugar Hollow.

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