Stream Report: The Doyles and the Moormans

My destination this morning was the Moormans River in Sugar Hollow -- the main stem -- where there are some very nice riffles above the first bridge as you go up the valley.  I had high hopes of finding lots of good things, but I ended up disappointed.  I saw quite a few small winter stoneflies, a good number of common stoneflies (genus Acroneuria), crane fly larvae, black fly larvae, one lonely Peltoperlid (Roach-like stonefly), one fingernet caddis, and two young Diploperla Perlodids.  That was it.  No large winter stoneflies --that surprised me -- and no variety in the Perlodids.  Still, I got a few nice photos which I'm happy to share.

1. The Roach-like stonefly (something I wasn't expecting)

2. One of the small winter stoneflies

3. The fingernet caddis (genus Chimarra) -- a real beauty.  In the last photo, the arrow points to the notch in the "frontoclypeal apotome" (the upper lip, as it were) that is characteristic of this particular genus.

4. The Diploperla Perodids, one of them recently molted and almost entirely clear!

5. And finally, one of the black fly larvae (genus Prosimulium), very unique in terms of the color.  (I've been starting to see black flies now in our streams, and there were quite a few on the leaves in the Moormans this morning.)

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Disappointed with what I found at the Moormans, where I worked pretty hard to find what I did, I decided to head to the Doyles.   Here I fared much better.  The leaf packs were loaded with insects, and the variety was what I expected to see.  I again found some small winter stoneflies and a few black fly larvae, but I was pleased to also see large winter stoneflies (both Taeniopteryx and Strophopteryx), Diploperla Perlodids, Helopicus Perlodids, and -- as in the beautiful photo at the top of the page -- Clioperla Perlodids.   I hope to do more work in the Moormans this year, so I hope I fare better in other locations.

Photos from the Doyles.

1. Another look at the Clioperla clio Perlodid stonefly -- this one's close to being fully mature.

2. One of the Taeniopteryx large winter stoneflies (Taeniopteryx burksi)

3. One of the Strophopteryx large winter stoneflies (Strophopteryx fasciata)

4. And a couple of shots of one of several Helopicus Perlodid stoneflies I found in this stream (Helopicus subvarians)

This is not a Perlodid stonefly that inhabits a lot of our streams.  To date I've only seen it in the Doyles and in Buck Mt. Creek.  It's a big one.  This one was about 3/4 inch long and it still has a long way to go.  Note that the wing pads have not yet started to curl and spread.

Are They the Best Streams I Explore? Tributaries to the Moormans in Sugar Hollow

They probably are.  Let me simply review the insects I found today in the small stream to which I went  on March 4th of this year for the very first time -- and I'll tell you their tolerance values.  The dominant taxon today: the Chloroperlid (Green) stonefly (photo above): TV = 0.2 (Sweltsa species).  A close second and third: the Giant stonefly, Pteronarcys scotti: TV = 1.8; and Roach-like stoneflies, genus Tallaperla: TV = 1.3.  I also found a number of Free-living caddisflies, both Rhyacophila fuscula: TV = 1.6; and Rhyacophila nigrita: TV = 0.0.  And if I'm right, I found a tiny Perlodid stonefly, Isoperla holochlora: TV = 0.0.  That's pretty impressive.  The only mayflies I found (I forgot to look under the rocks!) were Ameletids: at the most (if they were A. lineatus) the TV would be 2.4.

I'll come back to the "tiny Perlodids" (there were two of them) in a minute.  But let me first run through some of the photos that I took today.

1. Chloroperlids: genus Sweltsa.

2. Giant stonefly: Pteronarcys scotti

ventral view, showing the thoracic gills

3. Free-living caddisfly: Rhyacophila nigrita (I found three)

4. Free-living caddisfly: Rhyacophila fuscula (a young one)

5. Large Winter stonefly: Taenionema atlanticum

and one that had recently molted

6. Ameletid mayfly (genus Ameletus)

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On the Perlodid stoneflies I found -- there were several Clioperlas (that I kept out of my tray for the usual reason) and one Diploperla.  And then, there were these two tiny nymphs.  (Two photos of each.)

1.

2.

Can we determine the species?  Not with any degree of finality.  The genus is Isoperla for sure: the three dark bands on the abdomens are clear in each of the photos (and I checked the "Y" ridges and the laciniae).  But remember that the key thing in determining species -- well, one of the key things -- is the pattern on the head.  Here are some close-ups.

Nymph #1.

Nymph #2.

I'm not sure about 1.  It may be Isoperla namata (see the posting for 12/22).  On number 2. -- I wonder if this isn't a small Isoperla holochlora?  Here's a mature I. holochlora nymph that I found in this stream on May 18th.

Note the pale dots in front of the eyes, and note how they appear to be forming on the nymph found today.  And, note the pale "bell-shaped" space that lies in front of the anterior ocellus -- again, we can see that on the small nymph as well.

We'll have more challenges with small Perlodids in this particular stream as we move into spring.  Remember that this is one of the streams in which I found two Isoperla Perlodids that have not yet been identified to the level of species (see the posting of 5/18).

And, It Was.....A Fingernet Caddis Pupa!

The caddis pupa that I found at the Upper Doyles River on Thursday (12/22) -- in the photo above -- turned out to be a Fingernet pupa (family: Philopotamidae) -- genus Dolophilodes.  I may be the only one who wanted to know -- but I did want to know.  So, this morning I carefully removed the cocoon from its protective rock case: it slipped right out, by the way, it wasn't glued fast to the enclosure (this is important for genus ID).

For pupa identification, we have to use Merritt, Cummins, and Berg, eds., An Introduction to the Aquatic Insects of North America (Fourth Edition, 2008).  This key requires us to look at the dorsal (top) side of the abdomen and count the number of "hook plates" on each abdominal segment: critical, are the number of pairs on segments 3, 4, and 5.

As you can see, segments 3 and 4 each have one pair of hooked plates (which show up as little brown dots), while segment 5 has two.   Let's turn to couplet 2 for caddis pupae in Merritt, Cummins, and Berg (p. 460).

2.  Abdominal segments III, IV, and V each with two pairs of hook plates.....3
2'. Abdominal segment III with no more than one pair of hook plates, segments IV and V each with two pairs of hook plates, or two pairs of hook plates present only on segment V....4  (italics added)

Clearly, we have to move to couplet 4 -- not 3.

4. Abdominal segment IV with one pair of hook plates; segment V with two pairs of hook plates. ...
Philopotamidae
4'. Abdominal segments IV and V each with two pairs of hook plates ....5


No need to go on to 5.   This is a Philopotamid pupa -- Fingernet caddis.   I'm not surprised.  I've been seeing a lot of mature fingernet larvae in a lot of our streams throughout the fall.

And, we can be pretty sure this is genus Dolophilodes since the cocoon was not firmly attached to its enclosure.  Glenn Wiggins (Caddisflies: The Underwater Architects, p. 62) says the following on this point: "Moreover, in the philopotamid genus Dolophilodes the cocoon is not fastened to the interior wall of the dome but remains free; and if the dome of rock fragments is carefully pried from the rock substrate, the cocoon can be removed intact... ."  And here is the cocoon -- intact.  (Eerie!  It looks for all the world like the pupa is smiling!)

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Below, the "dome" enclosing the pupa as seen from above -- and a Dolophilodes Fingernet larva.

Where to Begin? A Stream Report on the Upper Doyles River

I suppose the obvious place to begin is with something new.  The flatheaded mayfly, Epeorus Pleuralis.
This is the "two-tailed" flatheaded mayfly with the large, fan-shaped gills that act as "suction cups" helping them to hold on to the rocks in fast current.  (And, yes, it is time to start looking under the rocks in addition to sifting through leaf packs!)  In the streams inhabited by Epeorus pleuralis, -- e.g. the Doyles, Buck Mt. Creek, the Rapidan -- this is the flatheaded mayfly that will dominate samples into the spring.  Tolerance value: 1.5.

I selected these two for my photos.  There were a lot of them on the rocks: many were still very tiny.
But, there were two other flatheaded species around: Maccaffertum vicarium and Maccaffertium x (meaning I'm not sure of the species, but whatever it is, it's big!).  The banding on the abdominal segments indicates M. vicarium right away, so too, do the reddish markings on the legs and the tails.

And here's the other Mac species: I'll work on the species ID when I have time.

I suspect the Epeorus flatheaded nymph would be the dominant taxon today if I had done a head count.  But I also found a lot of Green stoneflies (Chloroperlids), and they're starting to show their true colors.  In fact at this site, they're large enough now to confirm that the genus is indeed Sweltsa.

For the genus ID -- if we work through the key in Peckarsky (Freshwater Macroinvertebrates, p. 73), we come to a choice between:

48a. Inner margin of hind wingpads parallel to body axis; fewer than 6 short, coarse setae between compound eye and hind margin of head .... Haploperla
or
48b. Inner margin of hind wingpads angled away from body axis; more than 6 short, coarse setae between compound eye and hind margin of head .... go to 49.

The wingpads on the nymphs that I found this morning are big enough for us to see that they clearly "angle away from the body axis."

And, though they may be hard to see in this picture, there are certainly more than 6 coarse setae behind the compound eye.

So Haploperla is eliminated.  So too is Rasvena, since the dorsum of the abdomen is monchromatic and does not have "4 longitudinal dark stripes" (Peckarsky, couplet 49a./49b.).

That brings us to the following choice.

50a. Thick, black, depressed hairs present laterally on all thoracic sterna ... Sweltsa
or
50b. Thick, black, depressed hairs absent from lateral thoracic sterna; sternal hairs erect, light-colored ...
Suwallia


 Let's look at the chest.

These are Sweltsa Chloroperlids for sure.  The tolerance value for Sweltsa species is 0.2: we find these only in very good streams.

Perlodid stoneflies were also common today.  I found three different species: Clioperla clio, Diploperla duplicata, and a very small Isoperla namata.  Photos in order.

Now, how on earth do we know that this last Perlodid is Isoperla namata?!  The Isoperla ID can be established in the usual way with a microscope: look at the "Y" ridge and the shape and make-up of the lacinia.  But how do we know that it's the species namata?  It's the pattern that's taking shape on top of the head that gives that away.  This is the same pattern we see on mature, much more colorful nymphs.
Compare the two heads.

I. namata is the most common Perlodid species we see in our area streams, and we'll be seeing a lot of them in March, April, and May.

Just three other things.

1) A beautiful, fairly mature, Giant stonefly.  And as much as I want to work on species ID for the Giants, I couldn't bring myself to preserve this beauty so I could do the requisite microscope work.

2. I found more Uenoid caddisfly cases today adhering to rocks.  And the colors of the cases I found in the upper Doyles River were quite different than those I found only Tuesday at Buck Mt. Creek.  The larvae use the pebblies and sand that they have at hand.

3. And finally, I found a pupating caddis sealed away in its cocoon.  This is probably a free-living caddis or a fingernet caddis -- but we can only be sure by taking the pupa out of its sack.  In the ventral view, the pupa is quite visible inside its cocoon.

Dorsal view:

Ventral view:

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Oh.  There was one other thing.   I put the Clioperla nymph in a separate container this morning so it wouldn't eat the other insects for breakfast.  Unfortunately, when I put it into a petri dish for taking its photo, I left a Green stonefly nymph and a Small winter nymph in the tray with it.  And that was the end of the Small winter stonefly!