Isoperlas, Isoperlas, Isoperlas: Back to Sugar Hollow

The Perlodid stonefly Isoperla similis, one of several Isoperla Perlodids that I've only seen in two small streams in Sugar Hollow.   According to Beaty ("The Plecoptera of North Carolina," p. 24) this one is "relatively uncommon," and it's "collected from headwater Mountain streams and medium rivers during the winter and early spring." I do think of this small mountain stream as a "headwater" stream, even though there are smaller streams still that feed into it higher up on the ridge.

I. similis has a tolerance value of 0.8. and Beaty's description of the key features includes: "head brown with a pair of pale spots near labral suture, a pale M-shaped mark anterior to median ocellus and pale marks anterolateral to the lateral ocelli; abdomen brown with a light median longitudinal stripe and with a pair of faint submedian pale dots on each segment."  Let's have a look (best to click on the photo to enlarge it.)

The pale dots near the labral suture might show up even better in a second photo:

One more photo, taken in quite different lighting conditions (the sun was not very helpful today, peaking out through the clouds and then disappearing!)

Steven Beaty told me last year that the mountains in North Carolina and Virginia are richer in species of Isoperla Perlodids than anywhere else in the world.  And, you may recall that last spring I found two Isoperlas  in Sugar Hollow that even Beaty could not ID to the level of species (see the entries posted on 5/19, 5/21, 6/14, and 6/16)) -- both of those nymphs, by the way, were found in the stream that I went to today.  This is one of the two:

And today I was happy to see that this is a species that is a permanent resident here.  Look at this small version of the nymph in the photo above.  (Note the pale spot in the ocellar triangle, and the pale line that arcs between the rear ocelli.)

Finally, one more Isoperla in the insects we ran into today -- a very, very small Isoperla holochlora, even smaller than the one I found on Tuesday up at South River.  This is one of my favorite stoneflies, and I'm looking forward to watching them change as they mature through the spring.

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Two other insects to highlight from today's venture.

1. A very nice common netspinner caddis -- Diplectrona modesta.

2. And the flatheaded mayfly that only hangs out in "pristine" headwater streams -- Maccaffertium meririvulanum.

(Where you go when you want to see really good insects.)

Rhithrogena Flatheaded Mayflies and Diploperla Perlodid stoneflies: A Trip to the Lynch River

This is not a flatheaded mayfly that we see in a lot of our streams: last year I only saw them in Buck Mt. Creek.  But today they were all over the bottoms of rocks in the Lynch River.  They were prolific; this was the only flatheaded genus that I could find.

The "give away" feature for this genus of flathead is -- quoting from Beaty ("The Ephemeroptera of North Carolina,"  p. 22) -- "Abdominal gills 1 and 7 enlarged and meet ventrally forming a ventral disk."
This complete gill "oval" on the underside of the nymph is very clear in this microscope view.

Beaty also notes that this flatheaded genus -- in North Carolina, at least -- is "uncommon" and "intolerant" (the TV assigned in NC for the genus is 0.0), and that "A fair amount of color variation and overlap of characters can make Rhithrogena species determination difficult."  From the brief descriptions that Beaty provides of 7 possible species, the nymphs I was finding today could be R. uhari -- but that's just judging by size (5-7 mm) and color of tergites.

Knopp and Cormier (Mayflies, p. 137) note that Rhithrogena flatheaded mayflies produce an important hatch for fly fishermen in the West, the "Western March Brown."  But Rhithrogena is not considered important for fishermen in the East.  "Scattered populations of Rhithrogena species also inhabit certain East and Midwest freestone rivers but are not known to produce very reliable hatches."  I'd have to say that there will indeed be a "reliable hatch" of Rhithrogena in the Lynch River this spring, in fact it's probably already starting.  Here are pictures of two other nymphs that I found this morning -- I saw hundreds -- and note that the first is fully mature with the black wing pads.  (The second, by the way, since tergum "color" is important in species ID, might not be the same species as the other two that I've shown.)

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While the rocks in the Lynch were covered with Rhithrogenas, the leaf packs were full of Perlodid stoneflies, in particular, Diploperla duplicata.    We've been seeing these in various rivers all winter long, but they're starting to color up now as they start to mature.

This nymph was 12-13 mm long.  I did find Isoperla namatas, but they were outnumbered by far by the Diploperlas, not something I would have predicted.

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(More signs of spring in Virginia.)

Back From the South: Back "To" the South: Finding Cinygmula subaequalis

I wasn't sure where to go this morning, having been out of the streams for a week.  But I chose the South River up in Greene County, and it proved to be a good choice.

A new -- for me -- species of flatheaded mayfly: Cinygmula subaequalis.  When I first saw these -- I found two of them -- I thought I had found some early Heptagenia species.  Heptagenia marginalis, some may remember, is a flathead that I typically find in our streams in late summer.  It looks like this:

But the colors and patterns were not quite right.   So, I preserved one of the nymphs to look at closely using the microscope.  When I did that, I could not see what we need to see on Heptagenia nymphs -- fibrilliform behind each of the gills.  Fibrilliform is the feathery part of the gill that looks like this on a Heptagenia nymph:

Also note in this photo that the final gill of a Heptagenia nymph is smaller than those that precede it.  Now look at the gills on the nymph that I found this morning.

There is no fibrilliform visible behind any gill, and the gills are all the same size.  So, off I went to one of our keys in search of a flatheaded nymph on which fibrilliform is clearly absent.  So I looked in Peckarsky (Freshwater Macroinvertebrates, p. 31) where I read: "Front of head distinctly emarginate medially, maxillary palps normally visible at sides of head from dorsal view; fibrillifrom portion of gills absent or reduced to tiny filaments....Cinygmula."

So, is the head "distinctly emarginate," and are the maxillary palps "visible at the sides of the head" in a dorsal view?   The microscope clearly reveals that the answer is "yes" to both questions.

Let me add from Steven Beaty ("The Ephemeroptera of North Carolina, p. 17) the following things on Cinygmula --

1. "Genus diagnosis: Front of head incised medially; maxillary palpi protrude at side of head; all gills on segments 1-7 similar in size and shape; fibrilifrom portion of gills 2-6 absent or vestigial; three caudal filaments."

2. "In high quality mountain streams.  Collected March -- June."

3. "Cinygmula subaequalis is the only species in NC and is often confused with Heptagenia."

So there you have it.  A new species -- always makes my day.

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It was a banner day at the South River, one of those days that I ended up getting home late: too many good insects and too many photos to take.  The dominant insect?  The Perlodid stonefly, Isoperla namata, the leaf packs were crawling with them.  But that was just the beginning, so here we go with some photos.

1. Maturing Isoperla namatas.

2. A gorgeous brushlegged mayfly -- Isonychia bicolor.

3. A maturing green stonefly, genus Sweltsa.

4. Spiny crawlers, of course, both E. dorothea (first) and E. invaria (second).

5. Blephariceridae -- net-winged midges -- both the larvae (on the left) and the pupae (on the right).

6. Another Rhyacophila carolina freeliving caddisfly larva (note the burnt orange head).

7. And the "common" R. fuscula freeliving caddisfly, both larva and pupa.

And finally, two "first of the season" insects --

8. A Nemourid stonefly, genus Amphinemura, the one that is common in our streams in the spring.  Note the "frilly gills" that stick out from the neck.

8. And a Perlodid stonefly, Isoperla holochlora.

When this one grows up, it will look something like this. (note the similar pattern on the head)

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"Red buds" in bloom: a sure sign of spring in Virginia. (Streamside at South River)

Small Streams -- Special Insects: A Report on Sugar Hollow

I'm keeping track of the insects I only find in the small mountain streams in Sugar Hollow.   Here are photos of the taxa I've noted so far.  (The stonefly nymph in the photo above is one that I have found in the Rapidan River as well: this is the Perlodid stonefly, Malirekus hastatus.  Still, it's a rather spectacular picture.)
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1. The flatheaded mayfly, Maccaffertium meririvulanum.

2. The freeliving caddisfly, Rhyacophila nigrita -- in cream/gray and aquamarine.

3. The freeliving caddisfly Rhyacophila glaberrima (species ID is tentative).

4. The common netspinner larva, Diplectrona modesta.

5. The fingernet caddisfly larva, genus Wormaldia.

6. The small winter stonefly, Paracapnia angulata.

7. The Perlodid stonefly Isoperla similis.

8. A Perlodid stonefly, genus Isoperla, species not yet identified by the professionals.

9. Another Perlodid stonefly, genus Isoperla, species not yet ID'd by the professionals.

10. And the giant stonefly, Pteronarcys scotti (species ID is tentative).

In addition to the Malirekus hastatus at the top of the page, there are three other taxa that I've only found in the small streams in Sugar Hollow and in the Rapidan River: the crane fly larva, genus Hexatoma, the northern case-maker caddisfly, genus Pycnopsyche, and the large winter stonefly, Taenionema atlanticum.  These.

Oh.  And I've seen Lepidostomatids in the Rapidan -- and elsewhere -- but Sugar Hollow's the place to go for beautiful "mixed media" (sand grains and leaves) cases.

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I'll be in Florida -- golf and fishing -- through next Tuesday, March 27.  I hope to post a new entry on Thursday, March 29.