Friday, May 23, 2014

Drunella season: the spiny crawler Drunella cornutella at the Lynch River

I didn't know what I would find at the Lynch River this morning -- but I did not expect to see this: the spiny crawler mayfly, Drunella cornutella.  Of the three Drunella spinys that I've seen so far, this one tends to show up late in the season. D. tuberculata and D. walkeri can show up in April;  I usually see D. cornutella sometime in June.

D. cornutella has "tusks" -- well, I regard them as tusks -- "frontoclypeal projections."  And like all the Drunellas, it has very robust fore femora with sharp spines on the anterior edges.

I've already used Beaty's description to ID them (see the entry posted on 5/27/12), so I won't repeat all that he says ("The Ephemeroptera of North Carolina," p. 25).  But two key features are easy to see: "head smooth with moderately long lateral frontoclypeal projections but less than half as long as the distance between them; median ocellar tubercle blunt to moderately sharp."  You can judge the size of the projections yourselves using the photo above.  I'd call the median tubercle "blunt."

According to Knopp and Cormier (Mayflies, p. 224), Drunellas hatch as the "Eastern Blue-winged Olives."  Drunella nymphs can get pretty big so the adults must be the largest BWO's fly fishermen see during the season.  Tolerance values: D. cornutella, 0.0; D. tuberculata, 0.0; D. walkeri, 0.6.

The Drunellas:

D. tuberculata

D. walkeri

D. cornutella


Other photos:

1. Flatheaded mayfly, genus Rhithrogena.  This is actually what I was after this morning; this is one of the few places I've seen them.  Unfortunately, I only found one, and it was still very small.
This either means the Rhithrogenas are, like so many insects this year, showing up late -- or I found a late bloomer.  As promised, I'm not going to guess at the species.

2. Perlodid stonefly, Isoperla holochlora.  It's the only stonefly species I saw.  There were quite a few of them in the leaf packs (which were few and far between).

3. And the spiny crawler that's still around in large numbers -- Ephemerella dorothea.


Lynch River at Dyke Rd. in northern Albemarle county.  The water is still fairly high, but as you can see, our streams are dropping and clearing.

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