Saturday, May 12, 2012

Small Minnow Day -- Plauditus dubius -- at Buck Mt. Creek

I keep returning to Buck Mt. Creek in hopes of seeing Acentrella nadineae nymphs, one of the small minnow mayflies we see a lot in the summer.  I thought I had them today -- the colors looked right.  And, I found a lot of them; there seemed to be at least 2 or 3 on every rock I flipped over.  On one fairly large rock, there were five of them huddled together in the same spot.

It was when I uploaded my pictures that I noticed the problem: these nymphs have gray bands on their tails.  They were not A. nadineae nymphs.  My second thought was Plauditus dubius (see the entries posted on April the 10th), and this time I was right.

The one in the photo above is a mature female -- note the small eyes -- while the one in the photo below is a male (large, red eyes).  I think I saw more females than males.

On April 10th, I noted the features we look for in identifying this species, and the gray banding on the tails (caudal filaments) is among them.  For the rest, let me again note what Beaty says about the male colors and patterns.  "male -- enlarged medial spot on tergite 2 with 5-7 often dark; paired submedian spots on 3, 4, 8, 9 (spots on 5 obscured); sternites with lateral tracheation and segments 3, 5-7 often tinged with reddish brown." (Beaty, "The Ephemeroptera of North Carolina," p. 11)  All of those feature can clearly be seen in the following microscope photos.  (Actually, I'd say that almost all of the tergites are tinged with reddish brown.)

And for the tracheation on the sternites (ventral sides of the tergites) --

Plauditus dubius has a tolerance value of 2.2, and it appears to be a significant, late spring "Blue-winged Olive" hatch -- in fly fishing terms -- in Buck Mt. Creek.  But they're tiny, tiny insects, ranging from 3.0 -- 3.5 mm.  Some more photos of that beautiful female.


I didn't look for much else today -- I was after small minnow mayflies.  But I did, of course, find other things, including lots of Epeorus vitreus flatheaded mayflies.  Plus....

1. Another Drunella tuberculata spiny crawler mayfly, one with fairly dark wing pads.  (They like to root around in the silt.)

2. And there were several small Perlesta common stoneflies.  These tend to mature in June and July.

3.  And then there was this...

Pray tell!  It was the first thing that I picked up.  My first thought was "it's a small winter stonefly" -- but that's impossible at this time of year.  Second thought -- a very small Leuctrid (Rolled-winged stonefly), but that too seemed unlikely at this time of year, and I've never seen a Leuctrid in this stream.  But have a look at those tails.

It's a Chloroperlid -- a Green stonefly!  This is the first time I've seen Chloroperlids in Buck Mt. Creek, and it too seems out of season, especially one that's this small.  Elsewhere, in the small streams in Sugar Hollow, the Chloroperlids have been hatching for weeks.  I can't really explain this, but it is what it is.

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