Thursday, October 23, 2014

The common stonefly Acroneuria carolinensis -- or is it?!


I've had several e-mail discussions this year with Steven Beaty about genus Acroneuria common stones (Perlidae) -- a genus, he feels, is badly in need of re-search and revision.  This came up in April when I "might" have discovered an A. internata (see the entries of 4/20 and 4/22), and it came up last month when I found A. arenosa in the Rivanna, a nymph I had previously thought was a "brown" A. abnormis (see the entries of 9/1 and 9/4).   In those discussions, Beaty mentioned in passing that if I thought distinguishing those species from one another was tough, just wait until I tried to distinguish A. carolinensis from A. lycorias.

Huh.  I've seen -- I thought -- A. carolinensis a lot in the past -- and posted a whole lot of photos -- I've never looked for A. lycorias: I didn't know this ID was in doubt.
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I commonly find what I thought were A. carolinensis nymphs in the Doyles River at what I call my upper site, which is where I went this morning.  (Actually, I started at Patricia Byrom Park.  But with the small streams there virtually dry, I backtracked to the Doyles.)  So I thought I would look into this problem.

No problem finding the nymphs: I found two in short order.  The one at the top of the page (another photo),


and this one.


So, which are they, Acroneuria carolinensis or Acroneuria lycorias?  Let's look at Beaty's descriptions.  ("The Plecoptera of North Carolina," p. 14)

A. carolinensis - male nymphs 17-19 mm, female nymphs 21-23 mm; dorsum of head with light M-shaped pattern; dorsum of abdomen banded, anterior half light and posterior margin of tergites dark; anal gills usually absent.  Relatively common in the northeastern Mountains and in the Sand hills year round but particularly in the early winter.

Perfect fit.  Light "M" pattern, tergites banded, dark in back, no anal gills.


A. lycorias -- male nymphs 15-18 mm, female nymphs 17-20 mm; dorsum of head with light well-developed M-shaped pattern; posterior margins of tergites dark; anal gills usually present, sometimes small.  ... Found in Mountains (mostly the Catawba River basin) and Sand Hills.  Though uncommon, nymphs can be collected year round.

As you can see, the species seem to differ only in one way:  the presence or absence of anal gills.  Of course the catch is that accoring to Beaty they are usually absent on carolinensis, and usually present on lycorias.  That sort of leaves the door open!

Since we can't clearly decide on the species using Beaty's descriptions, let's see if there's other information around.  As it turns out the confusion of the two species was noted as early as 1942 by Frison (T. H. Frison, Studies of North American Plecoptera: With Special Reference to the Fauna of Illinois:  Urbana, Illinois, Natural History Survey Division, pp. 281-284).    On A. carolinensis he says-- "particularly important features of the color pattern are the arrangement of the light and dark areas on the dorsum of the head and the banding of the abdominal tergites; in color pattern the nymph is very similar to lycorias, but it differs from the nymph of lycorias in the lack of anal abdominal gills." (p. 282)  It would seem that at that time, at least, the presence or absence of anal gills was taken as definitive.  Perhaps things have changed.

Frison does one other thing that might be useful in deciding this matter.  He provides full illustrations of both of the nymphs (A. carolinensis, on p. 282; A. lycorias on p. 283).   In those illustrations, the head patterns are not exactly the same.   The carolinesis head looks exactly like the heads of the nymphs that I found this morning.  Note two things: 1) the wide, light area at the back of the head forms an arc that reaches up to the sides of the eyes, and 2) that light area intrudes into the dark transverse band on the head on either side of the ocellar triangle.  I.e. this is what we see.

e

Neither of those things is true on the lycorias head.  That is to say, the light area at the back of the head essentially forms a closed rectangle at the back of the head --it isn't shaped like an arc, and it does not intrude into the transverse band.  Also, it's completely surrounded by a dark border.


Hope your imagination is good: best I can do.
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What that all comes down to is this: I feel pretty confident that the nymphs that I'm finding are Acroneuria carolinensis, and I'll continue to use that ID.  But I will be checking for any sign of anal gills.

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Oh.  Lots of Strong-case makers in this river as well.  Psilotreta labida from what I can tell.


Saturday, October 18, 2014

Finally rain! Which of course produces bad photos


We have water again in our streams.  Unfortunately, the rain was so heavy -- at our house, I measured 3.5" -- that it muddied up a lot of the water.  And, that can lead to photos like the one at the top of the page.  (Lots of silt on the head and pronotum: on the case as well.)

Back to Sugar Hollow this morning to a small stream just to the west of the stream that I went to last week (10/9), not at all far away.  And last week, you'll recall, I found these beautiful, "clean," Goeras (weighted-case makers).



The heads and pronota are easy to see.  Not so when the larva is covered with silt.


Ah well...at least I'm pretty sure now that Goeras inhabit most -- if not all -- of these small streams I explore.

Species?  Again G. calcarata.  No sign of sternal plates (see the post of the 10th); and three pairs of sclerites on the metanotum.

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I didn't see  many insects today -- other than two Goeras.  There was a fair number of common stoneflies in the leafpacks (leaves are building up and decomposing) -- Acroneuria abnormis and Eccoptura xanthenses.  I was hoping to see the first Perlodid stones of the season: maybe next time.


Sunday, October 12, 2014

The seasons of the caddisfly case-makers


As you know, at the moment I'm seeing a lot of case-makers: humpless case-makers (Brachycentrids), strong-case makers (Odontocerids), and weighted-case makers (Goerids).  Case-makers show up in our streams in fairly predictable ways: I know when -- at what time of year -- I will see what.  True, there are some exceptions, notably the humpless case-maker Brachycentrus appalachia and the saddle-case-makers, Glossossoma nigrior.  My photo archives reveal that I can run into these larvae at just about any month the year.  Still, this is the pattern I most commonly see.

I. Winter (into Spring)

1. Uenoidae (little northern case-makers): species found so far -- Neophylax aniqua, N. concinnus, N. consimilis, N. mitchelli (in photo at top of the page), and N. oligius.  I have found them from late November right into April; they're most prolific from December through March. Cases made out of sand grains and pebbles, with 3-4 larger pebbles on each of the sides.

N. consimilis

N. aniqua

N. oligius

2.  Apataniidae (little mountain case-makers): species -- Apatania incerta.   Cases are made of mineral particles.  They are often cornucopia shaped with a "hood" over the top of the larva.  To date, I have found them only in December and January.




3. Glossossomatidae (saddle-case maker): species found so far -- Glossossoma nigrior.  The case is "dome" shaped, made of pebbles; it resembles the shell of a turtle.  When you turn the case over you can see the larva lying under a "strap" or "saddle."  I see a lot of these in the winter -- December through March.  But, I also see them throughout the summer -- May through September.  The summer cases seem to be smaller than those that I see in the winter (= two generations?).

dorsal view


ventral view


4. Lepidostomatidae (common name, Lepidostomatid).  Species -- undetermined.  The case can be made out of sand grains (early instars), a mix of sand grains and neatly cut sections of leaves (transitional), or the common 4-sided case made of square pieces of leaves (mature larva).  I see them most often in small mountain streams from late November through May.  However, I've found some as late as June in remote mountain streams, and they also inhabit the Rivanna in the summer.




from the Rivanna in summer (probably a different species)


5. Limnephilidae (northern case-maker): species -- Pycnopsyche gentilis.  This caddis larva often makes a 3-sided case out of sections of leaves/bark.  But the case can be part leaves and part stones, or -- especially in the late spring -- a case that's completely made out of pebbles.  They're in our streams from January through May.   The cases are fairly large.





II. Spring (into Summer)

1. Limnephilidae (northern case-makers): species  -- Pycnopsyche scabripennis.  These larvae make fairly large cases using sticks and pieces of wood.  I have found them from April through August.  Cases really vary in appearance and composition.



(Petri dish is 3 1/2" in diameter.)


2. Limnephilidae (northern case-maker): species --  Pseudostenophylax sparsus.  This one was found by my friend in Sugar Hollow in a spring seep right by her home.  It's rare.  The case is made of sand and pebbles.  She found it in March, so it's borderline Winter/Spring.   I've found some in late May as well.


3. Brachycentridae (humpless case-makers).  Species found so far: Brachycentrus appalachia, Micrasema charonis, and Micrasema wataga.   B. appalachia makes a 4-sided "chimney-shaped" case out of ribbons of vegetation.  The Micrasema cases are round and tapered, composed of vegetation and moss.   B. appalachia will be discussed with the Fall case-makers.  I have only found one Micrasema charonis, and that was in April.  My friend in Sugar Hollow found M. wataga larvae in June.

M. charonis


M. wataga (photo provided)

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III. Summer (into Fall)

1. Just a reminder -- I do find humpless case-makers (B. appalachia) throughout the summer, also saddle-case makers (small cases), and -- in the Rivanna -- Lepidostomatids.

2. Leptoceridae (long-horned case-makers): species found so far -- Nectopsyche exquisita and Ceraclea maculata.  N. exquisita is fairly common in the Rivanna with a case made of sand with plant stems attached.  I have found N. exquisita from July into October.  I have only seen C. maculata once, and that was in May.  (Guess I should put C. maculata into the Spring.)

N. exquisita



C. maculata

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IV. Fall (into winter)

1. Brachycentridae (humpless case-maker): species -- Brachycentrus appalachia.  While I have found these cases just about every month of the year, they are common on the rocks at this time of year, with the larvae being mature (they hatch in the spring).   The cases I see in the summer are small. The case is attached to a rock with the opening facing upstream since the larvae lacks "humps" with which it could generate water flow.


and next to Apatania incerta


2. Brachycentridae (humpless case-maker): species -- Adicrophleps hitchcocki.  This was found by my friend in a very small, first-order stream, buried in moss.  It is rare and regarded as threatened in the state of Virginia.  The case resembles that of B. appalachia, with strands of moss attached.  She found this one in November.  (She took the photo.)


3. Odontoceridae (strong-case maker): species found so far -- Psilotreta labida and Psilotreta frontalis (and possibly P. rufa).   Cases are made out of pebbles that are tightly glued together, often tapered and curved.  I've seen them as early as July, but they're most common from September into November.  Their cases are easy to see since they lie on tops rocks.  Psilotreta frontalis is a species I've only seen once: end of October.

P. labida



P. frontalis


4. Goeridae (weighted case-maker): species -- Goera fuscula and Goera calcarata.  Fairly large cases -- larger than those of Uenoids -- that are made out of pebbles, with 2-4 large pebbles on each of the sides.  I've found them from August through November

G. calcarata (2-stone case)


G. fuscula (in a 4-stone case)

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That's the case-maker cycle that I normally see -- at least in the stream work that I've done so far.  But if you monitor streams you want to be careful.    Things can show up "out of season," and you might find cases in the substrate long before they show up where I'm normally looking.   That being said, I've never seen a Uenoid in summer!

Thursday, October 9, 2014

Goera (Weighted-case maker) day in Sugar Hollow: in twos and threes and fours!


I knew that the water was low -- but I decided to have a look anyway -- so off to one of my favorite streams.  I didn't see much -- too early for the stoneflies and mayflies to fill up the leafpacks -- though I did see quite a few small Giant stones.  But there were Goeras all over the place.  How did I miss them in previous years?  Simple enough.  Their cases look exactly like little pebbles that are scattered on rocks.  But they no longer fool me.

I noted in the entry of 9/21 that Goeras are normally found in cases with two stones on each side.  But on 9/21 I found that nice case with four stones on each side.  Found another today (photo above), and I also found two that had three stones to a side.  Photos.  Two stones, three stones, and four stones.

Two



Three


and Four -- of which I got some very good photos.





Big case: 17 mm.
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What about species?  They all seemed to be G. calcarata -- though I have reservations.  I'd base the ID -- of G. calcarata -- on two things: 1) the larva has no sternal plates (see photos in the 9/21 entry), and 2) the central ridge of the pronotum is raised.



So why do I have reservations?  I'm not sure about the metanotal sclerites.  Do these larvae have 3 pairs of sclerites (G. calcarata) or 4 pairs of sclerites (G. fuscula)?   (This is the larva from the four-stone case.)


Beaty has assured me that the larva from the Rapidan River (previous entry) was indeed G. calcarata.


And the larva from Entry Run -- on which the sternal plates were very distinct -- I am sure was G. fuscula.


But I have trouble deciding about the larvae that I found today.  I'll let you know if I figure it out.
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We had an inch of rain two nights ago -- but we need a lot more to fill up our streams.  This is where I was looking today.


Here's a spot slightly lower last spring.