Wednesday, May 6, 2015

Drunella doddsi, a big spiny crawler from the Northwest: back from Portland, OR

It was a quick trip to Portland: our daughter's a Pastry Chef, and she's swamped with work at the moment.  But we did have time to go up to the Washougal River in WA, which is not far away.   And there we found a whole lot these...

Spiny crawler mayfly, Drunella doddsi.  Took me a while to identify this, the but key to use -- as always -- is Roger Rohrbeck's "Pacific Northwest Mayflies" at the following site:   There we find the following description of doddsi:

Body flattened; abdomen yellowish brown, w/o tubercles; thorax often lighter; head w/incomplete frontal shelf; ring of fine hairs encircling underside of abdomen; gills of similar size starting on seg. 3 ..
Body: reddish to dark olive brown. Wings: medium gray. Length: 13 mm. Tails: 3.   Emergence: Jul 10-30.

1. I'd say the color's right on -- more "reddish brown" than anything else.  The size of our nymph -- and it was fairly mature -- was exactly 13 mm.

2. There were no tubercles on the abdominal segments, contrary to most other species of this particular genus.  Were they present, they'd be on the posterior edge of some or all of the segments.

3.  The frontal shelf is clear in the live photos I took.  Here's a microscope view.  Also note the tubercles on the leading edge of the fore femora, one of the keys to the Drunella ID.

For a "complete" frontal shelf, we can look at a Timpanoga hecuba nymph.   (Montana, Blackfoot River, August, 2013.)

4.  There is indeed a "ring of fine hairs encircling [the] underside of [the] abdomen."

5.  And we can see the size of the gills, and the fact that they start on segment 3, in the second photo above.

Drunella doddsi slated to hatch as the "Western Green Drake" in June or July.  Given the number of nymphs that I saw on the rocks, there'll be a heck of a hatch on the Washougal!

(Now, I have to find out what this little nymph is.  I've been calling it Drunella doddsi -- apparently by mistake.  It's very small, and I've seen it in Oregon and Montana in August.  Hmm...


2.  Also found one of the stoneflies I've seen on a number of trips to Oregon and Montana: the common stonefly, Calineuria californica.


3. But the river was loaded with cases made by the "October caddis"  -- a Northern case-maker, genus Dicosmoecus.   When I was out here last year, I found a number of cases, the kind that are made by larvae that are still immature ( "The mature larva makes a long, tubular case out of pebbles [~ 30 mm] the immature larva makes a case out of a mixture of pebbles and sticks to which is attached pine needles.")   (For this description of cases, see the article by Michael P. Limm and Mary E. Power, cited in my entry of 5/1/14.)

For the genus ID, see the description provided by Wiggins in the same entry (5/1/14).  On the species -- I speculated last year that the larvae I found were Dicosmoecus gilvipes.  This year -- having found larvae that are more mature -- I could easily see what we needed to see to nail down the species ID.  There are only two choices: atripes and gilvipes.  Both have a fringe of sharp spines on the front edge of the pronotum.  But on the head, atripes has "miniscule spines," gilvipes does not -- it's "bald."  Clearly we've found gilvipes.

The Washougal was loaded with cases of D. gilvipes.   They were all over the rocks in the slow water on the sides of the river: had to be careful where you put down your feet.  But, I found immature cases, cases somewhat in "transition," and cases that were those made by larvae that are already fully mature (long, tubular, made out of pebbles).  Some photos of some of each.  (Not my best photos.  I had the ISO set too high, and I lost sharp definition.)

1. case made by an immature larva

2. both immature and mature

3. a case in "transition": the front has been changed over to pebbles; the rear is still sticks and needles.

And one of the more interesting cases I've seen.  About half way back from the front, it divides into two parts.

That's the view from above: in these photos, the case is turned on its side.

(I've not yet identified the flatheaded nymph that's perched on top of the case.)

All in all, a pretty good find, and it sure was a nice place to work.

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