Varieties of the common stonefly (Perlid) Acroneuria abnormis: back to the Rivanna

I had a doctor's appointment this morning that took me close to Darden Towe Park, so I decided to make a quick stop at the Rivanna.  The dominant taxon this morning was, as it was last week, the large winter stonefly Taeniopteryx burksi/maura, and I'll post some photos of one of those nymphs in a moment.

But I want to focus attention today on the common stonefly in the photo above, a nymph that I also found in the Rivanna.  This is one of the larger common stoneflies I've found recently with a body of 17 mm, cerci of 18 mm, and antennae of 13 mm.  So, from "tip-to-toe," as it were, this nymph measured 48 mm, roughly 2 inches (1.89 in., to be exact)!  It is probably an Acroneuria abnormis in terms of the species, the most common "common" we see, but let's come back to that in a moment.

In his description of Acroneuria abnormis nymphs, Steven Beaty notes that there are two different forms ("The Plecoptera of North Carolina," p. 14).

A. abnormis -- male nymphs 15-20 mm, female nymphs 25-30 mm; 1) 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 2) dorsum of head without M-shaped head pattern and abdomen uniformly brown; anal gills always absent.  Widespread and nymphs occur year round.  (I've added the 1/2 notation for clarification.)

Type 1 is the one that I normally see.  It looks like this:

The "M" pattern on the head is very clear -- not "interrupted" in this case -- as are the light colored posterior edges of the abdominal tergites.  There are no anal gills: rather, there is a fine silky setae on the inner sides of the cerci (tails) at the base.

As I browsed through my photos a short while ago, I also found, I think, a picture of the alternate form of A. abnormis: no "M" pattern on the head, and the abdomen is uniformly brown.  This was found on August 8 last year (2011), that means it was still on the "young" side, and the head pattern and abdominal colors could change.  Still, it does look quite a bit different than the nymph in the photo above: note the difference in the width and the length of the pronotum.

Now, let's look again at our nymph from this morning.

It's almost a hybrid of the two types that Beaty describes.  The abdomen appears to be "uniformly brown," but there does appear to be an "M" pattern on the head -- in this case "interrupted."

I sent a copy of this photo to Steven Beaty, and he was kind enough to reply.  His guess -- going by the photo -- would be that it is the "dark morph" of A. abnormis, but, he notes something important for us to remember.  There are still species of Acroneuria common stoneflies for which the nymphs have not been described (in his documents, he notes this is true for A. arida and A. petersi), so, ultimately, we have to be careful to declare an ID for a nymph that does not quite fit into the mold.

Interesting.  I should also note that I had found a similar common stonefly in the Rivanna at Crofton on 11/20 (last week).  Same abdomen, same head pattern, and same odd shaped pronotum -- very wide and somewhat narrow.

At first I thought this might be A. arenosa, another species on which the abdomen is totally brown.  But, A. arenosa has anal gills, the nymphs I am finding do not.  Always something new to explore.
______________

And now for some pix of one of the large winter stoneflies that I found this morning.  This is a male, and it was 8 mm: that's quite a change from the first one I found back on 10/28 -- one month ago -- which was a mere 1.5 mm!

_______________

("Dirty nymphs" -- All of the nymphs that I found this morning were "dirty," covered with silt.  The Rivanna River runs very muddy in times of high water, and I'm afraid in the fall and the winter, the leaf packs never clean up.)

Back to Uenoid species ID -- and a report from Sugar Hollow

I. Let me begin with the report.  I have not had very good luck in my recent stream visits: I haven't found a whole lot of insects, and I haven't found the insects I was hoping to find.   Last Wednesday (11/21) I went to the Rivanna at Crofton, looking for the Giant stoneflies that live in that river so I could check on the species ID.  I found nothing but large winter stoneflies (T. burksi/maura) and a few common stoneflies (genus Acroneuria) -- nothing to photograph.  On Friday (11/23) I tried the Rivanna at Darden Towe Park -- the exact same result, and the large winter nymphs were "dirty," in mudded up leaf packs.  That afternoon, I headed to Buck Mt. Creek, and you all know the results of that trip.

Yesterday, I decided to go to one of the small mountain streams in Sugar Hollow where I was sure I'd find a variety of small Perlodids -- I did not find a one, and again I did not see a lot of insects. But I did take a few photos.

1. The flatheaded mayfly, Maccaffertium merririvulanum -- tolerance value 0.5 -- the species that I've only found in these small mountain streams.  Identity is established by the pale "V" shapes on terga 5, and 7-9.

2. A fairly large fingernet caddisfly larva, genus Dolophilodes.  Genus ID is established by the asymmetrical (wavy) frontoclypeal apotome (front edge of the head).

3. Also visible in the photo above -- a freeliving caddisfly larva, Rhyacophila nigrita.  For the ID, note that the leading edge of the pronotum is darker than the rest of the pronotum.

4. And a Chloroperlid stonefly, genus Sweltsa.

I found other things of which I did not take any pictures: Giant stoneflies, big and small; small winter stoneflies, but nothing mature; common stoneflies, both Acroneuria and Eccoptura; and a few Peltoperlids (Roach-like stoneflies).  But I didn't see a single Perlodid, and the water was low, and the leaf packs aren't really forming.
__________________

II.  Now on to the question of Uenoid species ID.   The Uenoid case-maker (caddisfly larva) at the top of the page was found on 2/18/11 in Elk Run, a small tributary to Buck Mt. Creek.  The species is Neophylax oligius.

Let me tell you how I arrived at this species ID.  First, as I believe I mentioned last time, the caddisfly family Uenoidae consists of 5 genera: Farula, Neothremma, Sericostriata, Neophylax, and Oligophlebodes (see Glenn B. Wiggins, Larvae of the North American Caddisfly Genera Trichoptera), 2nd edition (Toronto: University of Toronto Press, 1996), pp. 413-415.)  The only genus that occurs in the East is Neophylax.  So, if you find a nice Uenoid case like the one at the top of the page -- with 3-4 large pebbles on each side of the case -- you not only know it's a Uenoid, you know it's a Neophylax Uenoid.  If you do not have the case, only the larva, you'll want to look for two things: 1) the leading edge of the mesonotum is "emarginated" (dented -- "anteromedial emargination"), in the shape of a "W," and 2) the ventral apotome is "T" shaped.

Steven Beaty lists a total of 10 species of Neophylax that might be found in North Carolina ("The Plecoptera of North Carolina," pp. 86-87).    However, his work group has never seen three of the larvae -- N. aniqua, N. atlanta, and N. kolodskii,  and two other species -- N. concinnus and N. toshioi -- have been found in parts of Virginia but not yet in North Carolina.  Of the rest, three species are said to be "common," the other two rare.  Common: N. consimilis, N. mitchelli, and N. oligius -- the "most common Neophylax in NC" (p. 87): uncommon: N. ornatus and N. fuscus.

The two most important characteristics used in establishing Neophylax species ID are 1) the presence or absence of ventral "clavate" gills on the first abdominal segment, and 2) the color of the head.  Let's look at the ventral side of the larva that lived in the case in the photo at the top of the page.

Clavate gills are gills that are wider at the tip than they are at the base (to me, they look like little balloons), and this larva clearly has them .  The front of the head is dark brown with a large, medial, yellow stripe.  Let me read from Beaty's descriptions:

N. oligius -- well developed clavate ventral gills on abdominal segment 1; yellow stripe on head, but varies, should be greater than 1/2 head length...underside of head usually testaceous [shell like].  Mountains and Piedmont. ... Most common Neophylax in NC.

I'd say that's what we've got.  And judging from the specimens that I've preserved over the years, I'm inclined to think that N. oligius is also the most common Neophylax in VA.  Almost every larva I have in my vial of Uenoids has the gills and has the yellow stripe on its head.

But, I have found additional species, some whose heads/faces are totally brown.  E.g. this one I found in South River on 1/4 at the start of this year:

and, the small Uenoid I found at Buck Mt. Creek on Friday had a brown head, and it did not have clavate gills.  (Only three of the possible species, by the way, do not have clavate gills: N. concinnus, N. toshioi, and N. fuscus.)

So, I have something fun to work on over the winter.  Can we identify all of our Uenoids to the level of species?  Stay tuned.

Good News and Bad News from Buck Mt. Creek

The good news is that I found quite a few Uenoid case-makers (caddisfly larvae) in Buck Mt. Creek this morning: the bad news is that someone is messing around with the stream.

Bad news first.  Buck Mt. Creek has changed dramatically since I was last there less than three weeks ago.  While the water is clear,  the bottom is, all of a sudden, silted up.  Rocks are covered with silt, the submerged leaves in the stream are covered with silt, and the grass-like vegetation that covers the bottom in places -- the long kind that sways back and forth with the current -- looks like it has "clouds" of silt on everyblade.  Result:  I didn't see a whole lot of insects, and most that I found -- whether in leaf packs or on the bottoms of rocks -- were covered with sand.  The brush-legged mayfly nymphs that I saw had turned pale in color: I'm not sure what that means -- but it can't be good.  If there are readers in the Charlottesville area who know what's going on, I'd sure like to find out about it.  It was very, very discouraging.  This is/was an excellent streams for insects.

Now, back to our Uenoids.  This is a caddisfly larva that makes its case out of grains of sand and small pebbles, and we see a lot of them in local streams during the winter.  You'll see their cases, normally, on the tops of the rocks -- they'll look like light-colored dots.  When its case is put upside down, the larva look like this.

The Uenoid genus we see in our streams is Neophylax, one of five genera noted by Wiggins in the caddis family Uenoidae (Glenn B. Wiggins, Larvae of the North American Caddisfly Genera (Trichoptera), 2nd edition [University of Toronto Press, 1996]).   But "Uenoidae" is a relatively new caddisfly family, and in 1977, in the 1st edition of Larvae of the North American Caddisfly Genera, Neophylax was listed as a Limnephilid (Northern case-maker) genus.

Uenoid cases are commonly tapered like the one in the photos above, and they often have 3-4 larger pebbles on each of their sides as we can see in this photo.

The cases that I found this morning were still very small, measuring 5-6 mm: the larvae inside were smaller still, about 3.5 mm.  And here's what the larva will look like when it slips out of its case.

Like most Limnephilids, the Unenoid has lateral humps on the first abdominal segment; there's a dorsal hump as well which we could see by turning this over.  But the key feature we need to see for certain ID is a "T" shaped sclerite on the underside of the head.   For a photo of this, see the entry posted on 12/21/10.

We'll be seeing Uenoids all the way through the winter, and I hope to be able to nail down the "species" ID sometime soon.  Beaty describes 10 Neophylax species that are found in North Carolina ("The Trichoptera of North Carolina," p. 86).

_______________

My other findings this morning?  A few small winter stoneflies, genus Allocapnia, but not a lot, and some Helopicus Perlodid stoneflies.

Whoops! Make that Nigronia serricornis

The hellgrammite/fishfly that I found yesterday at the Lynch was Nigronia serricornis, not Nigronia fasciatus.  I just discovered my mistake as I was looking for verification of the fasciatus ID.  The two species -- serricornis and fasciatus -- are similar, but they are distinguished from one another by the position and size of the respiratory tubes on segment 8.  These:

The tubes on N. fasciatus are relatively close together and long, extending beyond the end of segment 9; those on N. serricornis are "lateral" -- at the edges of the segment, and they are short, less than 1 mm in length.  This distinction is made in an article published in Entomological News in 1965 (R. Duncan Cuyler, "The larva of Nigronia fasciatus (Megaloptera: Corydalidae), pp. 192-195.)  On p. 194, Cuyler has this to say:  "Larvae of Nigronia fasciatus closely resemble the larvae of the more widespread Nigronia serricornis Say, and a third undescribed species.  It differs from these mainly in the greater length and closer proximity of the caudal respiratory tubules.  In the other species the respiratory tubules are mid-lateral in position, conical, and less than 1 mm in length."  The tubules on the nymph I found yesterday are less than .5 mm in length though that nymph was certainly not yet mature.

For more evidence on the ID of N. serricornis, I urge you to look at the illustrations of the respiratory tubes of N. serricornis and N. fasciatus in Merritt, Cummins and Berg, An Introduction to the Aquatic Insects of North America, on pp. 429 and 431.  Those of N. fasciatus clearly extend beyond the end of abdominal segment 9; those of N. serricornis do not.  Here is a microscope view of those of the nymph I found yesterday.

One final bit of evidence for us to consider.  Take a look at the Nigronia serricornis photos of Jason Neuswanger in Troutnut.com (http://www.troutnut.com/hatch/3357/Hellgrammite-Nigronia-serricornis-Fishfly), and note the length of the respiratory tubes.

My apologies for the mistake -- amateur at work.  The tolerance value of Nigronia serricornis is 4.6.
_______________

One strange looking Hellgrammite: Nigronia fasciatus

(Note: This hellgrammite is mistakenly identified in this entry.  It should be Nigronia serricornis.  See the following entry.)
Of course I should be talking about small and large winter stoneflies and all those Perlodid stoneflies that are showing up now -- but we'll be seeing them in a regular way in the weeks ahead, and this is an insect that we see only rarely.  It's a hellgrammite -- a "fishfly" if you prefer -- family Corydalidae, species, Nigronia fasciatus.  This is not the hellgrammite that all of us are used to seeing on the rocks in the streams.  That would be this one...

This is genus Corydalus, and it's got some pretty mean jaws (some of us have found out the hard way!).  The genera are similar in a couple of ways: both have two pairs of hooks at the end of the anal prolegs, and both have "filaments" sticking out from the abdominal segments.  But Corydalus has something you don't see on Nigronia nymphs -- clustered gills between those filaments.

Nothing like that on our Nigronia nymph.

I've already posted an entry on this type of fishfly (5/17 of this year), so I'd refer you back to that entry for the details on how we arrive at the genus ID.  Essentially it has to do with finding a pair of "respiratory" tubes at the end of segment 8 (dorsal side).  These:

Or these:

And note the size: 1 1/2 times as long as wide.  Nigronia.  The species ID, fasciatus, is determined -- as I recall (I can't locate my source at the moment) -- by the amount of separation between those tubes.  And one more photo, since the two pairs of hooks at the end of the prolegs are not clear in my live photos, here's a closeup microscope view.

Nigronia fasciatus.  This one is from the Lynch River.  Size: 25 mm.  Tolerance value: 6.1.

_____________________

So much for the "beast," let's have a look at a "beauty."

The Perlodid stonefly, Clioperla clio.  The Lynch was loaded with them.   Note how the posterior edges of the wing pads are really starting to bow, and of course, the colors and patterns are starting to richen as we watch them start to mature.

In addition to the C. clios, I did find a number of small winter stoneflies today -- one was eaten by this big Clioperla! -- and I found a number of tiny Perlodid stones that I was anxious to photograph and ID.  Unfortunately, on my way back to the car I stumbled and fell, and there went most of my insects!  I did find one still swimming around in my bowl.

A very, very small (2.5 mm) Diploperla duplicata.  I found a fully mature D. duplicata in this very same stream on May 14th of last year (2011).  Quite a transformation.

_______________

Below: a Clioperla clio traffic jam in my petri dish when I was getting my photos.

"Shock and Awe" at South River this morning

I was indeed "shocked" by two of the taxa I found at South River this morning, and I was in awe of the variety and numbers of insects I found in this healthy Greene county stream.

One of the shockers -- I found 3-4 Lepidostomatid caddisfly larvae including the one in the photo at the top of the page.  This is the case-maker we only see in small mountain streams, and we see them in large numbers, in some of those streams, during the winter.   It's only November...but they're already here.  Some Lepidostomatids, like the one in this photo, initially build their cases out of grains of sand, then switch over to a four-sided case made of neatly cut pieces of leaves.  The genus is Lepidostoma, and the TV is 1.0.

More photos:

1. another view of the larva in the photo at the top of the page

2. and a second case that appeared to be empty...

but wasn't!  Pretty cool.

And for shocker number two -- several tiny flatheaded maflies -- Epeorus pleuralis!

This one I did not even see until I started taking my pictures.

I'll see a lot of these in this stream in the winter and spring: but again, it's only November, and I never thought that I see them this early.   This is another insect that lives in small, quality, mountain streams with a tolerance value of 1.5.  Fishermen know it as the Quill Gordon.  You'll find these on the bottoms of rocks.  And in April, they'll look more like this:

_______________

And now for the insects I expected to see.  Without any question, the dominant insects in my findings today were the pronggilled mayfly, genus Paraleptophlebia and the small winter stonefly, genus Allocapnia.  The leaf packs were loaded with both of these nymphs, and I got some very nice photos.

Pronggilled mayfly, Paraleptophlebia

Small winter stoneflies, genus Allocapnia

1. Allocapnia pygmaea?

males:

female:

female and male together (the males are smaller than the females):

(Question:  Do the female wing pads lighten in color as they mature and the male wing pads get darker?)
_______________

And for the rest...

1. Chloroperlid stonefly, genus Sweltsa.  I found quite a few, all still very small.

2. A couple of small, free-living caddisfly larvae -- Rhyacophila fuscula.  You can see the "topless H" pattern on the head of the second.

 3. Giant stonefly, Pteronarcys proteus, "the Giant who lives in our small mountain streams."

4. A Perlodid stonefly, a very young Isoperla similis.

5. And still hanging around -- which is also a little bit "shocking" -- a Strong case-maker caddis, genus Psilotreta.

_______________

Below, the South River in the first photo: in the second, a tributary that flows into the South slightly downstream from where the first picture was taken.  At the moment, both streams are loaded with insects.