Isoperla season at the Rapidan River

If you follow this blog in a regular way, you know that the streams in our part of Virginia -- especially those in or near the mountains -- are rich in Isoperla Perlodid stoneflies (sometimes called "stripe tails").  The most common species we see is Isoperla namata, and I saw them in large numbers today.  But the Perlodid in the photo above is a small Isoperla nr. holochlora.  I was surprised to see one this early, but the Rapidan is the only stream in which I've seen this particular species.  (For a list of the Isoperlas I've found, so far, in our streams, see the entry posted on 9/8/12: for photos, see the entry for 10/3/12.)

The "nr." in Isoperla nr. holochlora stands for "near," since this species looks a lot like Isoperla holochlora.  But we can tell them apart with no need for a microscope view.  There are two things to check: 1) does the front part of the large yellow spot on the head merge with the labrum, or just barely touch it?  2) are there obvious longitudinal "stripes" on the abdominal segments?  If it's Isoperla nr. holochlora, the answers are "no": if it's Isoperla holochlora, the answers are "yes."  Have a look at these mature nymphs from last year.

They're both beautiful stoneflies.  But the Perlodid that we're more likely to see -- and in the spring, we see a lot of them in a lot of our streams (TV is 2.5) - is Isoperla namata.  This one.

They were a dime a dozen today in the leaf packs, and note that the wing pads on the nymph in the second photo are already starting to spread out from the body.
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The I. nr. holochlora was a surprise in my findings today: so too was this little small minnow mayfly, even though I was hoping to see one.

Baetis tricaudatus -- the first of the year.  This is a fairly intolerant small minnow mayfly with a TV of 1.5, so we only see it in clean mountain streams.  I've found them in the Rapidan, the South river in Greene county, and in some of the small streams in Sugar Hollow.  There are two ways to tell this one if you're using a loupe: 1) B. tricaudatus nymphs have a short, center tail with no banding on the tails, and 2) they have a thin, pale stripe that runs down the center of the abdominal segments.

And when they're mature they look like this (Rapidan River last winter).

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For the most part, I saw insects today that I expected to see, but the variety in this stream is really amazing.

1. Flatheaded mayfly, Epeorus pleuralis.  This is the most common insect I saw on the bottoms of rocks.

The wing pads are fairly long on this one as it prepares for the early spring hatch of "Quill Gordons."

2. Pronggilled mayfly, genus Paraleptophlebia.  These were common in leaf packs.

3. Spiny crawler mayfly, Ephemerella subvaria.  Always a favorite.

4. Spiny crawler mayfly, Ephemerella invaria.  Note the pale yellow stripe between the eyes.

5. Common netspinner caddisfly larva, Ceratopsyche alhedra.  This is the only common netspinner species I've seen up here in the winter.

6. Freeliving caddisfly larva, Rhyacophila fuscula.  This was a BIG one, probably an inch long.

7. Humpless case-maker caddisfly larva, Brachycentrus appalachia.

8. Lepidostomatid case-maker caddisfly larva, genus Lepidostoma.  I've never seen "mixed media" cases at the Rapidan River.

9.  Uenoid caddisfly larva, Neophylax consimilis.

10. And Uenoid caddisfly larva, species to be determined.

The water remains high in most of our streams -- but at least there was sunshine today!

Neophylax concinnus as the Uenoid I found at the Doyles: Making the case

The Uenoid caddis that I found yesterday at the Doyles appears to be Neophylax concinnus.  I'm not yet totally certain of this ID, but the evidence that I've compiled points strongly in that direction.  Let me make the case as I see it, approaching the issue in three different ways.


I. Elimination of other choices.

Steven Beaty's description of N. concinnus is brief: "without clavate ventral gills on abdominal segment 1."  ("The Trichoptera of North Carolina," p. 86)  That is certainly true of this larva.  Have a look.

I. e what is missing are these -- the balloon-shaped gills we find, for example. on N. oligius.

Of the Neophylax species that Beaty describes (pp. 86-87), only four lack clavate gills: N. aniqua, N. concinnus, N. toshioi, and N. fuscus.  Of these, N. aniqua and N. toshioi both have a "prominent tubercle on [the] head, often semi-blunt."  (Beaty, pp. 86-87)  The tubercle on N. aniqua looks like this:

There is no such tubercle on the larva I found yesterday.  There "might" be a very small, "pimple-like" tubercle on the head, but if there is, it's too small to show up in any photo I've taken.  But we can eliminate these three other species in additional ways.  N. aniqua, you will recall, is found in first order/headwater streams: this larva was found at a downstream location in the Doyles, close to its confluence with the Moormans.  N. toshioi, in addition to having a prominent tubercle on its head, has a head with a "pale eye stripe laterally" (Beaty p. 87) -- not true of our larva -- and it has "lateral gills on abdominal segments 2-5."  Our larva appears to lack lateral gills.  Finally, N. fuscus, like N. aniqua is a "headwater" taxon which is "relatively rare."  (Beaty, p. 87)

II. Confirmation of key features.

In. R. N. Vineyard, G. B. Wiggins, et.al., The Caddisfly Genus Neophylax, p. 46, we read: "Among larvae lacking gills on abdominal segment I [i.e. clavate gills], that of N. concinnus is distinguished by a combination of traits: short spines along the anterior margin of the pronotum, frequent presence of a small frontoclypeal tubercle, and pronotum with microsculpture of transverse rows of spicules."

1. There are short spines on the anterior margin of the pronotum of our larva.  But they are not easy to see through the layer of silt at the pronotum's edge.

2. As noted before, there "may" be a small frontoclypeal tubercle on our larva -- I'm not really sure.  However, the word "frequent" suggests to me that the tubercle is not always there and certainly not prominent.

3. And I think I can see a "microsculpture of transverse rows of spicules" on the pronotum.  The tiny black dots on the pronotum are very small spines.

This source also notes that there are spicules on the posterior of the mesonotum.  Those are quite clear in this photo.

III. Location, location, location

Vineyard, et.al., note that N. concinnus "occupies a wider array of habitats than any other single species in the genus" but that "it is generally found in small second- and third-order streams."  (p. 48)  I'd say that the Doyles fits into that group; I'd call it a second or third order stream.  Of greater interest still, this source notes that "Beam and Wiggins (1987) found that in southern Ontario streams N. concinnus occupied the longitudinal zone between N. aniqua (upstream) and N. oligius (downstream)."  (p. 48)  Perfect!  The N. aniqua larva I found was in a small stream in the Blue Ridge; the Doyles River near Whitehall is about 3 miles east of the Shenandoah National Park; and Buck Mt. Creek, where I normally find N. oligius larvae is about 10 miles more to the east.  So stream size and location also work in favor of this ID.

As I've already said, for me, at the moment, this ID is a tentative one.  I'll be sure to return to the Doyles very soon to see if I can find better samples.

N. aniqua

N. concinnus?

N. oligius

Finally sunshine -- finally back to the streams

The weather's been working against me.  I returned to VA last Thursday, to streams that were high and off-color, to gray cloudy days, and to temperatures that didn't get up to freezing.  At last, today it was sunny and warm.

This morning, I made a quick stop at the Doyles River, then I moved to Sugar Hollow to look at a small stream to which I've not been for a year.  Let me start there with a report on the insects I found.

1. In the photo at the top of the page, one of the most common things that I found, a Lepidostomatid case-maker caddis.  (According to Thomas Ames, by the way, the common name for this type of caddis is the "scaly-mouth caddisfly.")  I saw a lot of them -- always in leaf packs -- and most were in the "multi-media" cases: partly grains of sand and partly four-sided sections of leaves.

It's their time of year in these small mountain streams.

2. The common stonefly, Eccoptura xanthenses.  I saw several of them -- also a small mountain stream taxon -- and was surprised by their size.

3. Green stoneflies (Chloroperlids, genus Sweltsa).

4. And a Uenoid caddisfly larva, Neophylax mitchelli.  This is the one with the long, thin, backward pointing tubercle on its head.

I also saw quite a few flatheaded mayflies, the species we expect to see in this kind of stream at this time of year: Maccaffertium merririvulanum, Maccaffertium pudicum, and Epeorus pleuralis.  And there was a fair number of large winter stoneflies, Taeinionema atlanticum.
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Now, back to the Doyles.  The Doyles is still running high from all of the rainfall last week, but I did manage to find a few things of interest.

1. The large winter stonefly, Strophopteryx fasciata.  I did not see any Taeniopteryx burksi/maura -- they might be hatching.

2. The small minnow mayfly, Heterocloeon amplum.  I found quite a few, but they're still pretty small.  Still no sign of the rich colors we'll see later on.

3. And the spiny crawler mayfly, Ephemerella invaria.  You'll recall that this is the species we see in the winter: the spiny crawler "hordes" that invade our streams in the spring are E. dorothea.

Most E. invaria spiny crawlers have two visible distinguishing features: 1) the pale yellow line that runs between the eyes, and 2) paired tubercles on the posterior edges of abdominal segments 3-8.  On this nymph, each tubercle shows up as a light colored dot.

A closer look reveals those tubercles, as well as the posterolateral projections on segments 4-9.

4. I also found Uenoids at the Doyles River.  I only kept one, since I was sure they were N. oligius.  I was wrong, and I need to do some work on this larva before I decide on the ID.  I now wish I had kept a few more!

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Good to be back in business.  Sunshine again on Saturday -- or so they say at the moment.