Friday, May 17, 2013

Drunella day at the Doyles: Drunella walkeri, Drunella tuberculata (spiny crawler mayflies)

The spiny crawler, Drunella walkeri.  I've seen them before -- in the Doyles River and in Buck Mt. Creek -- but I've never seen one with these incredible colors.  Wow!

Actually, one of the things I was hoping to find today at the Doyles was a Drunella, but I was looking for Drunella cornutella.  This:

I found this one on May 26 of last year at my "upper" Doyles site,  close to the boundary of the Shenandoah National Park, which is where I started looking for insects this morning.  No luck.  But when I stopped at my lowest site on the Doyles, about 1 mile north of White Hall, I found a lot of Drunellas, but D. walkeri (TV, 0.6) and D. tuberculata (TV, 0.0).  But this walkeri was pretty special.

D. walkeri is described by Beaty in the following way:  "nymphs 8-10 mm; body setose; head roughened, with only small occipital tubercles and barely discernible lateral frontoclypeal projections; genae produced into sharp anterolateral projections; forefemur with long hair; abdomen with paired dorsal tubercles always well developed on segments 5-7.  Collected in late winter through spring.  Uncommon in the mountains."  (Steven Beaty, "The Ephemeroptera of North Carolina," p. 26)

The body is indeed very setose (hairy) as you can see in this photo: you can also see the long hair on the fore femora. (Click on the photo to enlarge.)

The genae are quite pronounced on this nymph and really stick out from the front sides of the head. They look like little horns.

And the tubercles on the posterior edges of the abdominal tergites show up as white dots on this particular specimen.

Quite a find.  It was even colorful when I flipped it on its back.

One of those insects that makes your day.


Drunella tuberculata.

Not nearly so colorful as our D. walkeri, but interesting nonetheless.  On D. tuberculata, Beaty has the following things to say. (p. 25)

D. tuberculata -- nymphs 7-9 mm; head with long occipital tubercles not divergent apically; frons without dark transverse band; abdomen with paired dorsal tubercles always well developed on segments 5-7.  Collected in spring and summer from rivers.  Uncommon.  Primarily a Mountain species.

Here is a good view of the occipital tubercles, and they clearly do not diverge apically, they might even slightly converge.  You can also see in this photo that there is no dark band on the frons (the face).

The tubercles on segments 5-7 are well developed though they might not be as clear as I would like in this photo.

(For more detail on how we identify D. tuberculata, see the entry of 4/23/12.)

Knopp and Cormier (Mayflies, pp. 224-227) do not mention D. tuberculata as important to fly fishermen, but they do list D. walkeri as one of five Drunellas that hatches as the "eastern blue-winged olive."  D. walkeri hatches in the northeast from July through September -- probably in June and July down here.  It must be a fairly big mayfly: BWO's  (vs. "eastern BWO's" are normally small, hatching from small minnow mayflies primarily in the spring and fall.

If you want to look for these nymphs, stick close to shore and look in patches of thick vegetation (leaf packs, root balls, bunches of twigs).   They will be in flowing water, but I never find them out in the fast flow of the stream.  Also look at the bases of patches of grass in the water.  Three of the five nymphs that I found this morning were on a small piece of bark submerged in the water.

They are often dirty, even covered in silt -- like this D. walkeri, one that I also found in the Doyles this morning.  Not all of them are as clean and colorful as the one at the top of the page.  But when you're crawling in root balls with those hairy legs and hairy body, this is what happens!

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