Thursday, October 20, 2016

While we're waiting -- the Perlodid stonefly, Clioperla clio

We're waiting for Bob's camera to be returned.  I was having "metering" problems: all of my macro photos in the last couple of months have been overexposed.  I used to shoot at a shutter speed of 1/60, or even 1/40, using a film speed of ISO 100.  But then I read that to avoid camera shake (blurred pictures) I should be shooting at 1/125 with a 60mm lens.   To adjust to that speed, I increased the ISO to 320, or even 400.  All of sudden in August, my photos were overexposed.  So I tried to adjust, increasing the shutter speed and lowering the ISO back to 100.  Still too light.  I went up to 1/250, even 1/320 -- still overexposed.  That's when I knew that I had a problem.  So the camera is being repaired.  Should be back sometime next week.

In the meantime, a couple of things.  The first, the species ID of this nymph.

I argued last month -- post of 9/24 -- that this was Acroneuria evoluta.  But last week I heard from an entomologist familiar with the stoneflies we find in Virginia, and he pointed out that he and Boris Kondratief -- the expert on all of these things -- have never found this species in our rivers.  He suggested that it was probably A. arenosa.  This is a problem I've noted before -- in my post of 6/12/15.  With the nymphs, the differences between arenosa and evoluta are slight.  On the top of the head of A. evoluta there is a faint "M" consisting of three lateral dots: on A. arenosa, those dots may or may not be present.  (You can see them on the nymph in the picture above.)  The other distinction is that the terga on A. evoluta are "uniformly brown, not banded," while on A. arenosa, the terga are "mostly uniformly brown but with an incomplete, narrow, pale anterior band."  (See Beaty, "The Plecoptera of North Carolina," p. 37 [vers. 4.0, 2015)  I've never seen that banding on the nymphs that I find, but, I've never found nymphs that are fully mature.  Maybe on those nymphs we'd see it.  In the end, the best way to establish species ID is by using adults (the terrestrials), and that's something I just don't do.  So, I can't claim to know for sure that my nymphs are A. evoluta -- could be A. arenosa -- and we'll have to leave it at that.

Now for the nymph at the top of the page.  When I finally get back to the streams, this is one that I'm likely to see: Perlodid stonefly, Clioperla clio.    But this is what they look like in the month of October.

It's always the first Perlodid stonefly I see, and it's very small in October, sometimes into November as well.

But they change in a hurry as we move on into winter.  Here's the progression.  (And note how the wingpads increasingly bend and diverge.)



February (also the one at the top of the page)

And by April, they're either almost mature or fully mature.

Pretty dramatic.

For the description of Clioperla clio we turn to Beaty, p. 52 (vers. 4).  "Robust nymph, 12-18 mm. Lacinia bidentate and mostly quadrate."

Yes.  "large, light medial area on dorsum of head (including most of ocellar triangle), a faint M-pattern sometimes present in ultimate instars; dark area along anterior margin sometimes with linearized anterolateral spots; dark bar along epicranial sutures almost connecting lateral ocelli to eyes, submental gills absent; pronotum surrounded by a dark border and with lateral edges pale; dorsum of abdomen with longitudinal stripes sometimes vague and diffuse; each tergite with up to 4-6 pale circular dots transversely across the segment, the 2 median dots often most prominent."



For a Perlodid stonefly, Clioperla clio is fairly tolerant -- TV of 5.2 -- consequently, I don't find it in the very best streams I explore (the small mountain streams in Sugar Hollow and the Rapidan River where it exits SNP).   On the other hand, I've never seen one in the Rivanna (a big river) where the insects are typically fairly tolerant.   It's the streams in between like Buck Mt. Creek and the Upper Doyles River.  There I see them in fairly big numbers.

Should be back at it by the end of next week.  Until then, I wait!

Saturday, October 8, 2016

A project for a rainy day: identifying that pupa

On September the 6th I posted an entry on the caddis pupa I'd found at the Rapidan River.  This one.

At the time, I speculated on the species ID suggesting three possible choices: Ceratopsyche/Hydropsyche sparna, Ceratopsyche/Hydropsyche slossonae, or Ceratopsyche/Hydropsyche alhedra, the three larvae that I've found in that stream.  But how to determine which one?

Well, I've been able to do it thanks to Jessica Fong, an Aquatic Biologist with the Toronto Conservation Authority who has helped me before.  She kindly sent me a key to Hydropsyche pupae:  Jane E. Rutherford, "An Illustrated Key to the Pupae of Six Species of Hydropsyche (Trichoptera: Hydropsychidae) Common in Southern Ontario Streams," The Great Lakes Entomologist, 1985.

The pupa was Ceratopsyche slossonae, and this is the larva.

(The pale spot in the middle of the head is a key feature of the species.)  How did I determine the species ID.

p. 128 of Rutherford's study: Pupa large, abdominal length 6.9-9.0 mm... with a dense patch of fine hairs present on dorsum of segment IV but the rest of the dorsal surface relatively hairless; left and right plates of each pair on segment III well-separated by at least 1 hook-plate width... H. slossonae.

The abdominal length of our pupa was a little over 7 mm.  Remember, our pupa looked like this.

But let's zoom in on segments 3, 4, and 5.

The dense setae on segment 4 -- vs. the paucity of setae on segments 3 and 5 -- is very clear, and as you can see, the space between the posterior hook plates on segment 3 is close to 3 times the width of the plates.

That will do it.  I love learning new things.  Thanks Jessica.

Saturday, September 24, 2016

Acroneuria evoluta: the Rivanna River at Crofton

These brown stoneflies were fairly common today at the Rivanna River at Crofton.  I picked up about 10 to look at for photos, and while I can't say for sure that they were all the same species, all three that I photographed were Acroneuria evoluta.   Here's Beaty's description.  "dorsum of head with interrupted M-shaped head pattern, appearing as a transverse row of 3 light spots in front of anterior ocellus; abdomen not banded; anal gills present.  Uncommon. ... Nymphs more common during summer thru late fall." ("The Plecoptera of North Carolina," version 3.3 [2011], p. 14)  The assigned TV is 1.7.  (For more on this ID, see the entries posted on 6/12/15 and 6/20/15.)

You can see the lack of abdominal banding in the photo above: and you can almost make out the 3 dots on the top of the head.  For the anal gills, let's draw in a little bit closer.

Another example

Actually, the 3 dots on the head might show up better on this very small nymph that I found (9 mm vs. 15 mm for the nymph at the very top of the page).

And the gills,

A. evoluta can be confused with the "brown" form of A. abnormis, the nymph that we looked at last week,

and I'm pretty sure that I've seen both nymphs at this site.  Both lack banding on the abdominal terga; both are brown.  But, remember that A. abnormis "brown" nymphs lack anal gills, and there is no "M-pattern" on the top of the head, not even light dots.

The Rivanna River at Crofton is the only site where I've found this species of common stone (Perlidae).  I've not seen it at Darden Towe Park in Charlottesville -- not yet anyway -- where the brown A. abnormis is common.    Moreover, it's a species that is not attested in the state of Virginia according to "NatureServe Explore" (  I've sent them my data, but so far I've been ignored.  Alas, the fate of the amateur entomologist!

I didn't see much else on the rocks in the Rivanna this morning, though I did see a few of these nymphs, Agnetina annulipes,

and there are still some damselfly nymphs kicking around

This nymph is a "narrow-winged" damselfly -- Coenagrionidae, genus Argia.

And this is what the Rivanna looks like at Crofton.

Friday, September 23, 2016

Habitat, species variation, and tolerance values: the common stonefly Acroneuria abnormis

I have written before about the issue of habitat and species variation -- in some detail on 8/26/15.  Let me remind you of two examples.

First, we have two Isoperla holochloras, one light and one dark.  Light,

and dark.

The light we find in all sorts of streams that vary in quality from Buck Mt. Creek, a stream that flows through pasture land, to the Rapidan River in the mountains at the entrance to the Shenandoah National Park (Graves Mill).

Buck Mt. Creek

the Rapidan River

But the dark form is one that I've only seen in the mountains.  In the Rapidan River, where it co-occurs with the light, and in a very clean tributary to the Rapidan River, the Staunton.

In fact, in the Staunton I've seen nothing but the dark nymphs.

Another case that I've mentioned before, Isoperla orata.  We have the "classic" form that we've found in the Rapidan River and in the small, pristine streams of Sugar Hollow,

and a variant form

which is also found in the Rapidan River, but I've seen it as well in the Doyles River and Buck Mt.
Creek, again, streams that are a step down in quality terms.

It seems to me that we have the same situation with the common stonefly, Acroneuria abnormis. A reminder of Beaty's species description.  "A. abnormis ... : dorsum of head with a well defined M-shaped head pattern, sometimes with interruptions; posterior margins of abdominal tergites light, dark tergal bands irregular; or dorsum of head without M-shaped head pattern and abdomen uniformly brown; anal gills always absent."  He adds "widespread and nymphs occur year round." 

I'd like to suggest that again, habitat is relevant in determining where these two forms are found.  The first, with the well defined M-pattern and the banded terga

is indeed widespread, and I see it in almost all of the streams I visit.   But in the Rivanna, we find the "brown" form (no M-pattern, and terga completely brown), a form that, so far, I've not seen anywhere else.

 (Not sure if the first type co-occurs in the Rivanna.  Something I have to look into.)  All of this makes me wonder about species variation and tolerance values.  It has to be true that the "brown" form of A. abnormis is more tolerant than the typical pattern we see, the same being true for the two types of I. holochlora and I. orata.  The NC list of tolerance values actually does distinguish between the light and dark holochloras: the former has a TV of 0.7, the latter is 0.0.  Makes very good sense.  But no distinction is made for our other two taxa.  There's only one value for I. orata -- 0.0 -- and the same is true for A. abnormis -- 2.1.   I think that there too, a distinction has to be made.

Have to contact Beaty on this one.  Could well be that this is one of those things that needs some revision.

Thursday, September 22, 2016

It's Acroneuria lycorias -- not carolinensis -- at Buck Mt. Creek

Kind of messed up today with my photos.  Somehow, I had my camera set to "Aperture priority" mode (Av) -- instead of the "Shutter priority" mode (Tv) that I normally use.  Unfortunately, I had not chosen an aperture setting, so all of my photos were overexposed.  Alas!  As you can see in the photo above, by editing we can make a partial correction -- but the shading doesn't look right.

Anyway, I was curious to see what this common stonefly -- an Acroneuria nymph for sure -- was in terms of the species.   You may recall that there are two species of common stone that look almost exactly alike: A. carolinensis and A. lycorias.   (See the entry posted on 12/11/14.)  This is A. carolinensis from another stream.

While I see this one a lot in the mountain streams that I visit -- upper Doyles River, Rapidan River, north fork of the Moormans --  in 2013 I realized that in Buck Mt. Creek, I was finding A. lycorias instead.  This one.  (photo taken on 10/20/13)

 (A. carolinensis, by the way, has a TV of 1.2; A. lycorias, 2.1.)  How do we tell them apart?  There are two ways in which they're distinct: 1) A. lycorias has anal gills; A.carolinensis does not: and 2) A. carolinensis has faint, medial, longitudinal markings on some or all of the terga, on A. lycorias such markings are missing.

If you look again at the A. lycorias photo directly above, you can see both of those features.  For contrast, here's a picture of another A. carolinensis.

So which one did we find this morning?  Medial longitudinal markings seem to be absent.

I was hoping for another A. lycorias nymph; so, so far so good.  But are anal gills present?  I couldn't see them.  So I brought this nymph home and used my microscope to get really close.  And voila!

Sure enough, there they are.

Back to the Rivanna tomorrow.  I've already corrected my camera settings!

Thursday, September 15, 2016

Fall Stoneflies in the Rivanna: Two things I "hoped" to find; two things I "expected" to find -- and a surprise netspinner

The common stonefly (Perlidae), Agnetina flavescens (Midwestern Stone).  This is a species that I've only seen once before.  That was on 11/9/13: the Rivanna River at Darden Towe Park (Charlottesville), the same place I went to today.  And I was hoping to see it.  Agnetina nymphs have a setal row on the occiput, and anal gills are present.  A. flavescens is described by Beaty in the following way: "head pattern roughly M-shaped with arms directed posterolaterally and almost interrupted; a light triangular pale area between lateral ocelli; dorsum of abdomen banded, with dark bands on anterior half of segment...apex of tergite 10 light with narrow dark pigment band interrupted mesally." ("The Plecoptera of North Carolina," p. 15)

We can see all of those features on this tiny nymph save one: the anal gills.

The anal gills require a microscope view.

There is also a feature not noted by Beaty in his description which seems to be characteristic of A. flavescens: terga 8 and 9 are both pale with a single dark spot in the middle of 8 and three dark spots in 9.

While A. flavescens is not something I commonly see in the Rivanna, A. annulipes (Southern Stone) is par for the course at this time of year, and I found that species as well.

Much darker than A. flavescens, and the apex of terga 10 on this species is totally dark.  Again, we have to go to the microscope if we want to see anal gills.

On the species of Agnetina, Beaty notes: "Nymphs occur primarily in the Mountains though can be found in the Piedmont.  Uncommon."  Interesting.  A. annulipes, at least, is present in pretty good numbers in the Rivanna.  (A. capitata, by the way, is uncommon.  I've only seen that one at the Rapidan River.)

While I was pleasantly surprised to see both Agnetina that are found in this river, I was not at all surprised to see two other stones.  The first, the "brown form" of Acroneuria abnormis.

The abnormis nymphs that we normally see have a very clear pale yellow "M" on the head, and the terga are banded.  But with this type of abnormis, the head lacks that "M" pattern, and, as Beaty notes, the "abdomen [is] uniformly brown." (p.15)  It was a young one -- note the posterior edges of the wing pads -- but it was already a pretty big nymph: 17 mm.  By contrast, the A. flavescens nymph was only 8 mm while the A. annulipes was a mere 6!

Also around -- quite a few of them, actually -- the Giant stoneflies Pteronarcys dorsata.

This is the only "Giant" that I see in the Rivanna, and it's the most tolerant Giant species with a TV of 2.4.  It's easily distinguished by a number of features.  1) the lateral angles of the pronotum are "produced"; 2) there are longitudinal stripes on the abdomen (usually 3-5, only 2 visible here); and 3) there are no lateral projections/hooks on the abdominal segments.  (See Beaty, "The Plecoptera of North Carolina, p. 28)


It was a good day for stoneflies at the Rivanna, lots of them crawling around in the leafpacks.  I saw very few mayflies, and very few netspinner larvae in a stream that's filled with them in the summer.  But I did pick up one to ID.

I was completely shocked when I looked at this through the camera.  It's a Macrostemum!  How do we know?  The "carinate, flattened head".  (Beaty, "The Trichoptera of North Carolina," p. 77)  Let's have a close-up look.

You can see the carina -- the raised ridge circling the top of the head -- in this photo, and if you can't tell how flat that head is, here's another angle to use.

And with these gills, these larvae should have no problem getting oxygen out of the river!

Species?  Don't know.  There are two possibilites: M. carolina or M. zebratum.  On both, the head is "reddish brown".  (Beaty, p. 77)  The difference -- the size of the tubercle near the eye.  This.

On carolina it's "large"; on zebratum it's small.  I'd have to see both species to know which one I've found.  This is a common netspinner that I always see in the North Fork of the Rivanna in summer, but this is the first time I've picked one up in the main river.  While this one is brown, those in the North Fork have always been green.  (Photo from 7/16/11)


It was a pleasure to get back out to our streams.  The Rivanna will be my destination for the foreseeable future.  We're in semi-drought conditions: most of our streams are dreadfully low and warm.