Tuesday, August 28, 2012

Two Confirmations, One Change (Serratella tibialis): Insects from Montana and Oregon


In identifying the insects I recently found in Montana and Oregon, I noted that some of my ID's were provisional -- precise identification to the level of species would require microscope work at home.  Having now done that microscope work, I can confirm two of my identifications -- but there is one that has to be changed.

The mayfly nymph in the photo above -- and the more mature nymph, same species,  in this photo --


 is not Ephemerella dorothea infrequens (the Pale Morning Dun), rather, it keys out to Serratella tibialis -- for fly fishermen, the Red Quill, or the Small Western Dark Hendrickson.  Remember that the difference between Ephemerella and Serratella spiny crawlers is primarily a matter of the hair on the tails: Ephemerella tails have a long silky fringe -- Serratella tails have only tiny black spiky hairs.  Take a look at this close-up of the tails on the second nymph pictured above.


Very clearly the tails of Serratella.  For the ID of S. tibialis, I turn to the description in "Fly Fishing Entomology: Pacific Northwest Mayflies."  "Abdominal segments 2-8 w/small sharply pointed tubercles on hind edge; rear edges of middle abdominal segments straight; often w/dorsal stripe down middle of abdomen; dark/light banding on legs."

The stripe down the abdomen is very clear in both of our photos, and we can see the banding on the legs in these photos as well.  For the "pointed tubercles" on segments 2-8, look at the following photos.


and


While the tubercles on segment 2 are not very clear in the photo of the abdomen of nymph #1, they can be seen in the second photo -- a photo of the more mature nymph of the two.  (Click on the photo to enlarge it: the tubercles show up as two, tiny black dots -- but they're hard to see.)
______________

For the confirmations -- the stonefly nymph in the photo below from the Salmon River in Oregon is, indeed, Calineuria californica.



And the stonefly nymph in this photo -- from the Clark Fork River near Missoula, MT -- is, indeed, Claassenia sabulosa.



1. On the Calineuria nymph -- there is only one species of Calineuria, C. californica, so all we have to prove is that this nymph is a Calineuria nymph in terms of the genus.  For this we must turn to Merritt, Cummins, and Berg, ed., An Introduction to the Aquatic Insects of North America (4th edition).  On p. 325-7 in that key, we can start our ID by looking at the occiput (back of the head).

55  Occipital spinules in a sinuate, irregularly spaced row, more or less complete behind ocelli.


That would be "yes," so we move to 56.

56  Ab terga with fewer than 5 or no intercalary bristles...Hesperoperla
56' Ab terga with more than 5 intercalary bristles...57

In the photo below, the caramel colored dots are "intercalarly bristles," and there are clearly more than 5 on each of the terga.




57 ... posterior fringe of Ab terga with numerous long setae whose length is three-fourths or more the length of Ab segments...Attaneuria
57' ...posterior fringe of Ab terga with numerous long setae whose length is one-fourth the length of Ab segments...58

In the photo above, I've drawn an arrow to the posterior fringe of one of the terga, and I'd say they are about 1/4 the length of the terga.  We move to 58 where the question becomes -- do the cerci have a "prominent dorsal fringe of long silky hairs"?  Look at the first photo above of our nymph.  Yes, they do have such a fringe.

With  couplet 59, we reach the difference between Doroneuria and Calineuria.

59  Dorsum of Th and Ab with a mesal, longitudinal row of long, fine, silky hairs; Ab7 sternum usually with incomplete posterior fringe...Doroneuria
59' No mesal longitudinal row of silky hairs on Th-Ab dorsum; Ab7 sternum usually with a complete posterior fringe...Calineuria





Our nymph does not have a "mesal, longitudinal row of long, fine, silky hairs," but Ab7 sternum does have a complete posterior fringe.  Calineuria -- specifically Calineuria californica.
______________

2. The identification of this nymph as Claassenia sabulosa is much easier.  Again, there is only one species of Claassenia in the Northwest -- C. sabulosa -- so we just have to show that this is a Claassenia nymph in terms of the genus.


Having established that the occiput has a "transverse row of regularly spaced spinules," and that it has three ocelli, not two -- both of which we can see in this photo -- we move to couplet 53 in Merritt, Cummins, and Berg (p. 325).

53  Ab terga with more than 5 intercalary bristles...Claassenia


The carmel colored spots are intercalary bristles, and clearly there are more than 5 on each of the terga.
Claassenia sabulosa.  Some of you may recall that I found a  mature C. sabulosa in Rock Creek near Missoula last year.


It really turns into a very colorful nymph.

_______________

Below: 1) the Clark Fork River near Petty Creek; 2) typical scene on the Blackfoot River.



No comments:

Post a Comment