The Uenoid caddisfly season begins: "Little northern casemakers" at Lickinghole Creek

With the forecast for Sunday through Wednesday not looking real good, I decided to get out today before the nasty weather moves in.  Where to go?  Well, I hadn't been to Lickinghole Creek in Crozet for a very long time, and it's a good stream to look for Uenoids, so I thought I'd give it a try.
And hooray, hooray, I found a Uenoid -- the first of the season!   It was a very small larva -- 5 mm -- but it still made a very colorful case.

I thought it would probably be the common species Neophylax oligius, but when I looked at my photos I was uncertain about that ID.  Take a close look at the head.

According to Beaty -- "The Trichoptera of North Carolina," p. 87 -- N. oligius has a "yellow stripe on [its] head" which "should be greater than 1/2 [the] head length."  I.e. it should look like this.

That's not quite what we have.  So, what about Neophylax consimilis which has a "stripe or pale area which is less than 1/2 [the] head length"?  (Beaty, p. 86)  N. consimilis looks like this.

Here was my quandry -- was the larva I found N. consimilis, or was it a "young" N. oligius on which the stripe on the head was not fully developed?  Toughy, especially since Beaty notes that the head "stripes" on these two species often blend into one another.

In the end, I had to look at the underside of the head.  On N. consimilis the underside of the head is "usually dark" (Beaty, p. 87); on N. oligius it's usually "testaceous" (brownish red or brownish yellow).  Here's how they differ.

N. consimilis:

N. oligius:

Which do we have?  I'd say it's N. oligius with a stripe that's not yet as long as it's going to be.

Here's a microscope view of the underside of the head on which you can also see the "clavate, ventral gills"  (they're found on both of our species.)

Sorry.  That's a long way to go to establish a species ID, but I like to figure them out when I can.
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Other photos today...lots of small winter stoneflies.

1. Small winter stonefly, Allocapnia pygmaea.

2. Small winter stonefly, Allocapnia mystica.  (Note the different shape of the pronotum and the "burnt orange" abdomen.)

3. And of course, there was at least one Clioperla clio Perlodid hanging around.

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Welcome back to the Uenoids!

Rolled-winged stoneflies (Leuctridae) and Small winter stoneflies (Capniidae): How to Distinguish the Nymphs

For many stream groups, the fall sampling season is over.  But if you're still out with your tables and nets, or if you plan to look at some streams in the next 2-3 months, there's a good chance that you'll find Leuctrids (rolled-winged stoneflies) and Capniids (small winter stoneflies) at the same time in the same place.  These nymphs can be confused, but you should be able to tell them apart.  Best advice -- look at the wing pads.

1. Rolled-winged stoneflies: genus Leuctra

The wing pads on Leuctrids on long and slender -- finger-like -- with those in the rear being shorter than those in the front.   All four wing pads are uniform in width from beginning to end: the sides are essentially parallel.   However, the front wing pads are widely separated, those in the rear are not, they're close together.  The front wing pads are so wide apart that the inner edges of those pads overlap the outer edges of the rear wing pads.
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I've found two genera of Capniidae in our streams, so we must look at them one at a time.

2. Small winter stoneflies: genus Allocapnia

Allocapnia small winter wing pads differ from those of Leuctra in two significant ways.  Note that those in the rear are not the same shape as those in the front: they are wider than those in the front, and the bottoms are flat/truncated.   In addition, while those in the front are further apart than those in the back, the inner edges of the front wing pads do not normally overlap the outer edges of those in the rear.

3. Small winter stoneflies: genus Paracapnia

Paracapnia wing pads are actually pretty close in appearance to those of Leuctra.   The front and the rear are much the same shape.  However, they tend to look more like "tear drops" than "fingers": they are wider at the top than they are at the bottom.
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There is one other thing you can look at when you're trying to distinguish Leuctrids and Capniids.  Note the length and shape of the abdomens.   The abdomen of the Leuctrid is long and thin, and like the wing pads, it's the same width from beginning to end -- parallel-sided,  pencil-like.  The abdomen of the Capniid (both genera) is somewhat shorter, and it tends to be slightly wider in the middle than it is at either end -- i.e. it's tapered, cigar-like.
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Now, the wing pads and abdomens tell the tale if you've got a nymph that's mature or fairly mature.   What if you find one that's tiny, one where the wing pads are not very well formed?  Answer: you can't ID them in the field.  Preserve them and take them back to the lab.  And if you're the one who's stuck with the ID work back at the lab, what then do you look for?

Well, you can hope that the shape of the wing pads and/or the shape of the abdomen will be more easily seen with a microscope.  But certain ID depends on seeing "pleural" or "ventrolateral" folds on the abdominal segments.  It can be tough.  But here's what you're trying to see.  (Put the nymph on its back or its side.)

1. Capniids -- all Capniids -- have ventrolateral folds on all nine abdominal segments (See Beaty, "The Plecoptera of North Carolina," p. 1.)  They look like this.

2. Leuctrids have ventrolateral folds on the first four abdominal segments only.  (Beaty, p. 2)

Best I can do.  Good luck!

The "Strong-case makers" Psilotreta labida and Psilotreta frontalis: revisiting the issue of identification

I went to the upper Doyles River this morning where I found -- among other things (photos later) -- this Strong-case maker, Psilotreta labida.  If you look back at the entry posted on 10/29 you'll see that I found a Strong-case maker that day that I thought might be the species Psilotreta frontalis -- though at that time I was not totally sure.   I'm now fairly certain of that ID, so I thought I'd take this opportunity to revisit the issue.

1. Psilotreta labida -- Doyles River, 11/19

The head was so black on this larva that at first I wasn't sure it was P. labida, but as it turns out, that's a key to species ID.  Let's review.

P. labida -- larvae up to 13 mm; coloration variable, usually frontoclypeus entirely black with broad stripe extending to occipital foramen and usually darker than P. frontalis; pronotum with dark stripe broad sometimes nearly obscuring ground color; anterolateral pronotal projections long and acute; mesonotum nearly all dark.  Spring fed and larger streams.  (Steven Beaty, "The Trichoptera of North Carolina," p. 97)

Since the nature of the pronotal "anterolateral projections" is a key distinction between our two species, let's look at that first.

No question, they're long and acute.   But is the "frontoclypeus" entirely black, the dark stripe on the pronotum broad, and the mesonotum "nearly all dark"?

Using this microscope view, I'd answer "yes" to all of those questions.  Psilotreta labida.

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2. Psilotreta frontalis -- tiny stream at Montfair Farm, 10/29

Now to the larva -- actually there were several -- we found on 10/29.   While the "coloration" of P. frontalis is, like that of P. labida, "variable," Beaty does note some slight differences in the colors of the pronotum and mesonotum.  "dark on pro- and mesonotum confined to middle stripes and lateral edge; pronotum with anterior edge slightly darker than ground color."

In the photos below, the differences with P. labida in terms of the pro- and mesonotal colors are quite pronounced.

The mesonotum, in particular, is quite a bit lighter on P. frontalis.  And then, there are the anterolateral projections on the pronotum: on P. labida they're "long and acute"; on P. frontalis they're "relatively short."

They sure are.

There's one other way to distinguish P. frontalis from P. labida: habitat.   While P. labida can be found in "larger streams," P. frontalis seems to only be found in small head-water streams that are spring fed -- i.e. first order streams.  This point is made by Beaty, but by other authors as well.  Thomas Ames, for example, notes that, in contrast to P. labida,  "P. frontalis favors smaller streams" (Caddisflies, p. 214), and Ernie Schweibert comments "Psilotreta frontalis seems most abundant in small streams."  (Nymphs, Volume II, p. 135)  The stream I explored on 10/29 was one of the smallest streams I've looked in for insects: it was clearly a first order stream.  We do indeed have two Strong-case makers that live in our streams.

One final point.  I sent my "P. frontalis" photos to Steven Beaty and asked his opinion.  He agreed that they looked like frontalis.  However, he added that the real test to see if a larva is labida or frontalis is to check the setal pattern on the head, "particularly the length of seta 15 and 17."  Oh dear!
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Most of the insects I found today at the Doyles could be expected at this time of the year.  Just a few photos.

1. Small winter stonefly, Allocapnia pygmaea.  Seeing small winters in significant numbers now.

2. Large winter stonefly, Taeniopteryx burksi/maura

3. Pronggilled mayfly, genus Paraleptophlebia.  The most common taxon in the river today.

4. Perlodid stonefly, Helopicus subvarians.

5. And this odd-looking Perlodid that had just recently molted.

It too turned out to be Helopicus subvarians!  Should have known it by the "mask" on the face.