Focus, the "Agnetinas" (Common stoneflies, genus Agnetina): annulipes, flavescens, capitata

This morning I went out to the Doyles where, having gotten out of my car, I expected to find nothing at all: the water was just barely flowing.  We need lots of rain.  Nonetheless, I decided to turn over some rocks and sort through some leaf packs.  I didn't see very much, but there were quite a few little Perlids (common stones).   At first I dismissed them as baby Acroneuria abnormis nymphs, a common sight in a lot of our streams at this time of year.  But, they were very small, and -- I thought -- too dark for abnormis.

As soon as I looked at them through my lens, it was clear that they were Agnetina annulipes.  As you know, I commonly see this species in the Rivanna in late summer and fall (see the post from 9/11), but this is the first time I've seen them at the Doyles.

There are three Agnetinas: annulipes, flavescens, and capitata, and I've found all three in central Virginia.  The common name is the "Southern Stone": they're found from PA down to FL, and across the south into Alabama, Mississippi, and Louisiana.  Agnetina nymphs have two features in common, two features defining the genus: they have a complete setal row at the back of the head (occiput), and they all have anal gills.  They are also, according to Beaty, uncommon ("The Plecoptera of North Carolina," p. 15).  That may explain why, to date, I've found flavescens only one time, and the same for capitata.  A. annulipes, on the other hand, while I don't see it in a lot of our streams, I do see a lot in the Rivanna at this time of year, and without looking real long, I picked up four nymphs today at the Doyles, all of them in the leaf packs.

Here's how we tell the species apart.

I. Agnetina annulipes

This is a nymph that I found in the Rivanna last year (9/18/13), on which we can see all of the critical features: the occipital setal row, the anal gills, and in addition -- following Beaty -- the arms of the "M" pattern on the head point to the rear, tergum 10 is mostly dark, and the terga are banded with the anterior edge of each tergite being dark.  Not common enough to establish a tolerance value.

II. Agnetina flavescens

This is another nymph that I found last year (11/9) in the Rivanna.   It is similar to annulipes -- with some exceptions.  1) Note that tergum 10 is this case is light, and 2) the pattern on the wing pads is totally different: it somewhat resembles the symbol for batman!  Not common enough to establish a tolerance value.  I hope to find more of these in the Rivanna this fall: it's one of things that keeps taking me back.

III. Agnetina capitata

I've only found one: on 5/26 of this year at the Rapidan River.  As I've noted before, this species is "listed by NC Natural Heritage Program as Significantly Rare (2010)."  (Beaty, p. 15)  Again, a quite distinct pattern on the wing pads.  And in addition, the banding on the tergites is different than we see on the other two species: here the dark bands are on the posterior edges of the terga.  One more thing noted by Beaty, the "posterior margins [of the terga are] dark and with a triangular mesal area anteriorly projecting forming an apparent mid-dorsal longitudinal stripe."  That stripe is easy to see on this nymph that looks to be fully mature.(Beaty, p. 15) Not common enough to establish a tolerance value.
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I sure was surprised to see annulipes at the Doyles River this morning.  I love surprises!

Framing some photos: what to use?

I have a wall in my lab that's in need of a picture.  So I thought -- "Why don't I pick out four of my favorite photos from those that I've taken over the years and frame them?"  Seems fitting.

These were my choices.

1. In the photo at the top of the page -- the Perlodid stonefly, Isogenoides hansoni.  Love the colors, love the composition.

2. A second Perlodid stone -- Helopicus subvarians.

3. Two case-makers lying side-by-side: the humpless case-maker, Brachycentrus appalachia, and a small, little mountain case-maker, Apatania incerta.

4. And the weighted case-maker that I just found on Sunday, Goera fuscula.  Such an unusual case.

Should make a nice picture -- but I had to leave so many things out!  For example...

I. Stoneflies

1. Giant stonefly, Pteronarcys biloba.  Great colors, and this one is almost fully mature.

2. Another Perlodid stonefly, Malirekus hastatus.  They're killers -- but they sure are pretty.

3. And a third Perlodid, Isoperla orata.  This one is rare -- Rapidan River, of course.

4. A common stonefly (Perlid), Acroneuria abnormis, the "brown" kind.

5. Small winter stonefly, Allocapnia pygmaea

6. And one of the smallest stoneflies we see, a Leuctrid (needle fly), genus Leuctra.

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II. Mayflies

1. A rare one, the spiny crawler mayfly that I find at the Rapidan River, Ephemerella subvaria.

2. And a real beauty, the small minnow mayfly, Acentrella nadineae.

3. Another small minnow mayfly, Baetis tricaudatus.

4. And another small minnow mayfly, Heterocloeon amplum.

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III. Caddisflies

1.  The free-living caddisfly larva, Rhyacophila nigrita.

2. And another case-maker, a Lepidostomatid, genus Lepidostoma.  What an awesome case.

Hmm...maybe I need to make it a poster.  With all of this beauty out there, be careful where you walk when you step into a stream!

Buck Mt. Creek in the autumn, and some notes on Giant stoneflies

This morning when I went out to Buck Mt. Creek, I wasn't expecting to see a whole lot -- and my suspicions were right.  This is not the best time of year to be looking for insects.  Things are small, and a lot of mayflies and stoneflies are still in the substrate just starting to grow.  I know a lot of groups that monitor streams like to sample in September and October -- I don't always understand why.  Do we really get a good sense of the insects that live in our streams by looking this early?  You can find netspinners -- but they tend to downgrade the stream.  You won't see a lot of stoneflies -- which upgrade the streams -- until November and December.  By then most groups have stopped going out.  I'd venture to say that a lot of volunteers have never seen a small winter stonefly (Capniidae) or a large winter stonefly (Taeniopterygidae) if they don't sample from November -- February.  That's a shame.

Anyway, I didn't see anything that I wanted to photograph today -- save for the stream itself (note the water is low).  Saw some flatheaded mayflies, some small brush-legged mayflies, one small minnow mayfly, a few netspinners and fingernet larvae -- all of them small, and quite a few A. abnormis Perlids (common stoneflies), none even close to being mature.  I guess the rivers to do at the moment remain the Rivanna, the Rapidan, and Entry Run/South River.
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I. Giant stoneflies.

You'll remember that I picked up this Giant -- Pteronarcys biloba -- at Entry Run on Sunday.  And since we'll be seeing a lot of Giants from now through the spring, I thought I might note the "quick" way to distinguish the three species I've encountered so far: P. biloba, P. proteus, and P. dorsata.   For full details, see Beaty, "The Plecoptera of North Carolina," p. 28.    But to tell them apart, you only need to examine the pronotum (especially the corners) and the sides of the abdominal segments.

1. Pteronarcys biloba

On P. biloba nymphs, the front corners of the pronotum (anterolateral angles) are "conspicuously produced into hook-like processes." (Beaty)

But what we can see right away are the "lateral projections" or "hooks" on abdominal segments 1-8.  As I noted, they were very pronounced on the nymph that I found on Sunday.

Additional photos of P. biloba nymphs.

2. Pteronarcys proteus

This is the species I find in very small mountain streams, but it's in the Rapidan River as well.  The front and rear angles on the pronotum are not at all produced, no hooks whatsoever.  "Anterolateral projections on pronotum reduced, barely discernible."  (Beaty)

As for the abdominal lateral hooks, they're visible, but they're "appressed" (Beaty).  I.e. they don't stick out nearly so far as those we see on P. biloba, and they are only distinct on segments 1-6.  The projection on segment 7 is small; that on 8, barely discernible.  Also worth noting, the cerci (tails) on the P. proteus nymphs I have found are much shorter than those on P. biloba nymphs.

Some other P. proteus photos.

3. Pteronarcys dorsata

And we have Pteronarcys dorsata, the most tolerant of the Giants.  It's the only species I've seen in the Rivanna, but I've also found one in Buck Mt. Creek.  On the pronotum, "the lateral angles of [the] pronotum [are] produced, anterolateral ones almost hook-like." (Beaty)  Actually, the rear angle is virtually "pointed."

For the sides of the abdominal segments, there are "no lateral projections on [the] abdominal segments." (Beaty)  Sure can't argue with that.

Some additional photos of P. dorsata.

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That's all there is to it.  Tolerance values: P. biloba, 0.0; P. proteus, 0.4; P. dorsata, 2.4.

Entry Run yields a Goerid (Weighted-case maker) with an uncommon case

I wasn't sure what to make of this case when I saw it this morning.  This kind of case is common with the Uenoids -- 4 large pebbles on either side of the case used for ballast, and a case that is tapered.  But this case was big -- 16 mm -- much too big to be a Uenoid, and in any event, it's pretty early to see a Uenoid.  Of course, it' not too early to see Goerids (Weighted-case makers): you'll recall that I found this one last week at the Rapidan River

and I found this one this morning in South River, right next to Entry Run.

But Goerids, as we can see from these photos, have "squarish/rectangular" cases with 2 stones on each side, not 4.  There was simply no doubt that this one had 4.

But when I started taking my photos, it was clear that I had found a Goerid, just one with a very unusual case.  As I was taking the photos, I could see the sharp anterolateral points on the pronotum and the mesonotal anterolateral projections, hallmarks of this genus.

When I got home, I re-examined my sources which had this to say on the cases made by Goerids.

Beaty ("The Trichoptera of North Carolina," p. 87): "Case: Similar to that of Neophylax [i.e. Uenoidae] but with a continuous row of larger ballast stones laterally, usually two."

Wiggins (Larvae of the North American Caddisfly Genera, p. 226): "Case: With a row of larger pebbles along each side of the central tube of small rock fragments, larval cases of Goera are similar only to those of Neophylax in North America.  Generally, Goera cases have fewer and larger ballast stones on each side, usually two; Neophylax cases usually have smaller ballast stones, thus more than two."

Ames (Caddisflies: A Guide to Eastern Species for Anglers and Other Naturalists, p.232): Their cases have lateral ballast stones similar to those of Neophylax in Uenoidae, but they are more symmetrical and rarely have more than two stones on each side."

So, lesson learned Goera cases -- on occasion --  can have more than 2 ballast stones on the sides.
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Both of the Goerids I picked up this morning turned out to be Goera fuscula -- a "rare" species according to Beaty.  Key features: "4 pairs of sclerites on metanotum; sternal thoracic plates distinct."

Here we can see the 4 sclerites on one side of the metanotum

and the sternal thoracic plates look like this.

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Not much else to get excited about today at the stream -- which is typical for this time of year.  But I did find a young Pteronarcys biloba Giant stonefly.  Previously, I've seen nothing in Entry run but Pteronarcys proteus.

The "lateral projections" on the abdominal segments of this particular nymph were really impressive!

And as I suspected, I saw a lot of Strong-case makers, Psilotreta labida.

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Fun day.  Love it when we learn something new.  Goera fuscula.

dorsal view of case:

ventral view of case: