Tuesday, January 28, 2014

The freeliving caddisfly larva "Rhyacophila banksi" in Sugar Hollow -- but it's a "complex"

I was sorting through my photos on Sunday and found this one: it's a free-living caddisfly larva, the photo dated 12/11/11.  I found this in the little stream in Sugar Hollow to which I returned yesterday.   I had made no attempt at species identification.  But the larva was preserved in my collection so I decided to give the ID a try.  I've concluded that it's R. banksi -- or better, part of the R. banski complex -- which in turn is part of the R. invaria group.  The R. banski complex includes the following species: R. alabama, R. banksi, R. carolae, R. kondratieffi, R. shenandoahensis, and R. parantra.   (See A.L. Prather and J.C. Morse, "Eastern Nearctic Rhyacophila Species, with Revision of the Rhyacophila invaria Group," Transactions of the American Entromological Society 127 (1): xx-xx, 2001, pp. 104-106.)

How do we arrive at the R. banksi ID?  To identify species of Rhyacophila you must examine the anal prolegs.  Three questions: 1) do they have "apicolateral spurs"?  2) are there "basoventral hooks"?  and 3) are there "ventral teeth" on the anal claws?  We find all three, for example, on Rhyacophila fuscula.

apicolateral spurs

basoventral hook (a dark, hooked sclerite at the base of the anal proleg)

and ventral teeth (in this case two)

Members of the R. invaria group do not have apicolateral spurs or basoventral hooks: they do have ventral teeth on the claws.

Steven Beaty says very little about the R. banksi complex: "larva ?? mm; head broadens posteriorly and without a conspicuous pattern."  ("The Trichoptera of North Carolina," p. 60) It is very clear in my photos that the head does broaden from front to back.

But there is a very detailed description of the species R. banksi, along with illustrations, in an article by J.S. Weaver and T.R. Illand Sykora: "The Rhyacophila of Pennsylvania with larval descriptions of R. banksi and R. carpenteri", Annals of the Carnegie Museum, 48 (1979), pp. 403-423.  Let me quote from that work (as cited in an unpublished manuscript by Joe Giersch and Robert Wisseman):

"R. banksi -- Overall length 16 mm, Head: Coloration variable; in some, golden brown, in others dark brown with an irregular row of pale muscle scars extended on each side of the front and the coronal suture, muscle scars faintly distinguishable on the frontocephalis, lateral and posterior portions lighter; right mandible with three apical teeth, mesal tooth longest; left mandible with two apical teeth, ventral tooth longer; maxillary palpi with second segment twice as long as the first.  Abdomen: Proleg with basoventral and apicolateral processes, neither free of membrane; claw with one large ventral tooth and sometimes a smaller tooth.  Flint (Roback, 1975) was of the opinion that "it is impossible to separate the larvae of R. invaria, R. shenandoahensis, and R. vibox."  Likewise, we are unable to distinguish the larvae of R. banksi from these three species."

(Prather and Morse could not distinguish the larvae of R. banksi, R. shenandoahensis, and R. parantra.)

The head of our larva, viewed through a microscope, is largely dark brown with muscle scars along both of the sutures and muscle scars in the frontoclypeus: those at the rear are very light.  It is an exact match, by the way, to the illustration provided by Weaver and Sykora and a close match to the illustration of R. parantra in Prather and Morse (p. 163).

While our article says that apicolateral spurs and basoventral hooks are present, it adds that neither is free of the membrane -- which is to say they're not  "present" in the way that they are on something like R. fuscula.  (You can see the sclerite on our larva -- but it's not really "hooked".)

There is one large tooth (denticle) visible on each ventral claw, possibly a second which is quite small.

Clearly, I need to check the "mandibles" with care -- but I'd rather have a second larva before I dismember the head of the only one in my collection.  One other thing -- the pronotum of R. banksi, as illustrated by Weaver and Sykora, is an exact match to the pronotum we see on our larva.

I think there's good reason to feel that the larva I found in December 2011 was indeed a member of the R. banksi complex, though clearly this ID is a tentative one.  But if that is true, it would mean that I've now found five Rhyacophilids in this one little stream.

R. fuscula

R. nigrita

R. glaberimma

R. carolina

and now R. banksi (one of the "complex")

That's pretty special.  But this is a real special stream.


(Hmm... is this the same insect?  Same stream on 3/14/11.  Rhyacophilids are "predaceous," and that Chloroperlid's in trouble!)

Monday, January 27, 2014

Nigronia fasciatus: the hellgrammite we find in small streams

I was about to call this one "Beauty and the Beast" -- no question about who's the "beast"!   But come photo time I couldn't locate the "beauty" -- a colorful, fully mature, Allocapnia small winter stonefly.

I had to get out there today before, once again, the temperatures take a dive, so off to my favorite small stream in Sugar Hollow in search of Rhyacophilids (freeliving caddisfly larvae).  I didn't find any, but it was still good to get out and turn over some rocks and sort through the leaf packs.

The hellgrammite we normally see is this ugly brute...

genus Corydalus.  But on occasion we run into the genus that lacks those frilly gills that we see on Corydalus.

The genus is Nigronia, and I've encountered two different species: N. serricornis (Lynch River -- see the postings of 11/21 and 11/22/12) and N. fasciatus.   They differ in the location and the length of the breathing tubes on segment 8.  These.

On N. serricornis, the tubes are short -- less than 1mm -- and fairly wide apart.  (For a full discussion of how to distinguish the two, see the Lynch River posting, 11/22/12.)  On N. fasciatus, the tubes are long, extending beyond the end of segment 9, and they're fairly close together.  The tubes on the large nymph that I found this morning measured about 1.5 mm: N. fasciatus.  Overall length was 33 mm.

One wierd looking critter!  Seems out of place in this pristine mountain stream.


I saw a lot of insects this morning, everything but the larva I was hoping to see.  The most common nymph that I found in the leaves was the large winter stonefly, Taenionema atlanticum.

And on the rocks: sides and tops, lots of Uenoids; bottoms, Epeorus pleuralis flatheaded mayflies -- they're plentiful at this time of year.

Oh, and by the way, I now feel quite certain that the Epeorus I found up at South River on 1/9 of this year -- this one

-- was Epeorus fragilis, not the more common Epeorus pleuralis.  Note the shapes of the heads and the shapes of the eyes.

I saw a lot of Uenoids this morning.  I hoped to run into N. mitchelli and/or N. aniqua -- which I find up at the top of this stream -- but alas, the four that I kept were all N. consimilis.
Unfortunately, I won't get up to the area where I know I will find mitchelli and aniqua until the weather warms up and we get rid of the snow.  N. consimilis: note the pale, reddish spots on the head.

They sure make beautiful cases in this little stream.

Below: young N. fasciatus found on 5/16/12.

Tuesday, January 21, 2014

Large winter stoneflies: how to distinguish Taenionema nymphs from Strophopteryx nymphs

At the moment we're seeing all three of our large winter stoneflies: Taeniopteryx burksi/maura (probably burksi), Strophopteryx fasciata, and Taenionema atlanticum.   These are all photos that I've recently posted.

T. burksi/maura:

S. fasciata:

T. atlanticum

T. burski/maura nymphs are already hatching: S. fasciata and T. atlanticum will probably start hatching sometime next month.  It is common to see T. burksi/maura and S. fasciata in the same streams, and I sometimes see T. atlanticum and T. burksi/maura together (like Sunday at the Rapidan River);  I don't know that I've ever seen T. atlanticum and S. fasciata in the same riffles. T. atlanticum nymphs prefer mountain streams, especially headwater/1st order streams.

Now, to my point.  When I first found Taenionema nymphs I was told by entomologists to be sure they were not Strophopteryx nymphs.  When you look at the photos above you'll wonder how on earth the two species could be confused.  Strophopteryx fasciata is very distinct: the head, pronotum, and thorax (wing pads) are mottled -- a mix of yellow and brown -- and the abdomen is clearly banded;  Taenionema atlanticum is totally brown.  Here's the catch -- while there is only one Taenionema species found here in the East (atlanticum), there are three Strophopteryx species here in Virginia  -- S. appalachia, S. fasciata, and S. limata -- and, S. limata, like T. atlanticum, is totally brown and is also found in the mountains (Beaty, "The Plecoptera of North Carolina," p. 7; Stewart and Stark, Nymphs of North American Stonefly Genera, p. 238).

So if you're out sampling this winter and start seeing brown, large winter stoneflies, chances are good that you've run into T. atlanticum nymphs, but there's the odd chance that you've found S. limata.  How to be sure which you have?

All Strophopteryx nymphs have a "ventroapical plate" which you can see by placing the nymph on its side.  It looks like this on S. fasciata.

But, Taenionema nymphs have this feature as well.  So you need a direct, head-on, as it were, view of the ventroapical plate.  This is how you tell the two species apart.

Strophopteryx ventroapical plate.  The plate is narrow and bends in at the sides.

Tanenionema atlanticum ventroapical plate.  The plate is broad, and the sides move down in a uniform way.

(For good illustrations of both ventroapical plates -- and how to distinguish the male from the female -- see Stewart and Stark, pp. 237 (Strophopteryx) and 240 (Taenionema).  There are probably very few readers who will need to make this distinction -- but that's how it's done.

With predictions of snow and freezing cold weather about to move in, I made a quick trip yesterday to the Doyles River in search of our "winter" small minnow mayfly, Heterocloeon amplum.  I did find a few, but they're still very small.

It will be quite awhile before we see the beautiful mature males and females.

Always something to which we can look forward.

Sunday, January 19, 2014

Quality insects in quality water: Isogenoides hansoni at the Rapidan River

It's a stunning insect and it's uncommon: the Perlodid stonefly, Isogenoides hansoni.  The Rapidan River in Madison County is the only stream in which I have found it.

The genus is defined by anatomical features.  It has "submental gills at least twice as long as [their] greatest width," and the "median ridge of [the] mesosternum extends anteriorly beyond [the] fork of [the] Y to [the] transverse ridge."  (Barbara Peckarsky, et.al., Freshwater Macroinvertebrates of Northeastern North America, p. 71.)   Naturally, we need microscope photos for a look at these features (these are photos of a previous nymph; I did not keep the nymph that I found today.)

For the species ID, let's turn to Beaty.  "I. hansoni -- nymphs 16-24 mm; large denticles on the ventral mandibular tooth; conspicuous, sharply delineated M-shaped pale mark anterior to median ocellus; ocellar triangle bordered by dark but with pale central spot; dark transverse bands on anterior third to half of terga 1-9 and a dark, transverse band along each posterior margin.  Relatively rare.  Recorded from GSMNP."  ("The Plecoptera of North Carolina," p. 22)

I can't be sure of the length of our nymph, but my guess would be ~ 20mm, and I have not looked at the "ventral mandibular tooth".  The other features are easy to see in the following photo. (Note that I marked the "median ocellus" as the "anterior ocellus".)

Even better:

(For a more detailed description of Isogenoides, see Stewart and Stark,  Nymphs of North American Stonefly Genera, pp. 403-406.)

Beaty notes two other things of interest about Isogenoides: "Primarily collected in small streams to small rivers in the Mountains from late September through April" and "Nymphs have been documented as inhabiting steams that support trout populations." (pp. 22-23)  A good description of the Rapidan River.

I've been fortunate to see at least one of these nymphs at the Rapidan every year since 2011.  Always makes my day.


Other photos.

1. Large winter stonefly, Taeniopteryx burksi/maura.  Fully mature (black wing pads, black prontum.)

2. Large winter stonefly, Taenionema atlanticum -- of which I got a very nice photo.

3. Pronggilled mayfly, Paraleptophlebia (mollis?).  The leaf packs were loaded with these, along with brushlegged mayflies and Isoperla montana/sp. Perlodid stoneflies.

4. One of the many Isoperla montana/sp. Perlodids I had in my bowl -- and returned to the stream.

5.  And naturally I picked up a few Uenoids (little northern case-makers).  They turned out to be Neophylax consimilis.  Loved the case on this one.

This one too.


And these are the riffles inhabited by I. hansoni -- though I always find them in leaf packs.  (Photo taken last spring.)