It's the annual "spiny crawler" invasion: Ephemerella dorothea

Actually, they're kind of a nuisance at this time of year.  For the last 3-4 weeks, when I sort through my tray to see what I've collected, it's hard to get past these spiny crawlers.  It has to be one of the biggest hatches all year, and they come out as -- in fly fishing terms -- PED's, Pale Evening Duns.  Early on in the year we tend to see Ephemerella invaria, but Ephemerella dorothea dominates the invasion each spring.  The main clue for the ID -- no turbercles on the posterior edges of the abdominal terga.

In a previous life when I monitored streams, I had the impression that when spiny crawlers dominated our net counts, we had hit upon a poor quality stream.  Just not true.  It's just what we run into at this time of year.  This morning I was at one of our headwater streams in Sugar Hollow.  My tray was loaded with them.  I normally ignore them when I'm taking photos, but I thought the colors on this one were nice.
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My search for Isoperlas continues, but I think I'm too late for anything but I. holochlora.  Still, I found this mature Isoperla sp. VA on May 18 in 2011, so there's hope.

I know Steve Beaty would LOVE me to rear one of these till it hatches.  We need an adult to detemine species ID, and, this could be a brand new species.
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Two nice pics from this morning.  The first, a flatheaded mayfly, Maccaffertium pudicum.

And the second, a pair of small Perlestas.  Guess they do inhabit these cold, mountain streams.