Monday, January 30, 2012

New Stream: New Genus of Small Winter Stonefly: Paracapnia

I knew there was something wrong with these wing pads -- so I preserved this nymph for further study.
This one too, a less mature nymph, but one that looked much the same.

Here's the problem -- all of the small winter stoneflies I found in December were genus Allocapnia.  The hind wing pads on Allocapnia nymphs look like this:

They're short and stubby, and the rear edge is essentially flat (truncate).  Now look at the wing pads on the nymph pictured at the top of the page:

Quite different.  The front and rear wing pads are shaped much the same, and the rear edge of the hind wing pads is "rounded"!    So, time to look at Peckarsky (Freshwater Macroinvertebrates, p. 66) where it becomes readily apparent that these are Paracapnia nymphs.  First time I've seen them -- or at least the first time I've identified them.

Peckarsky on Paracapnia: "Numerous conspicuous bristles, mostly along posterior margins of abdominal terga and bordering pronotum and wingpads...head with a dorsal, purple-brown, reticulate pattern [marked by crossing lines], meso- and metathoracic wingpads rounded."

1) I'll let you decide for yourself about the head pattern -- but it looks good to me. 2) We've already seen the rounded wing pads.  3) What about the "hairy" body.  Here's a look at some of the abdominal terga:

That fits.  4) Now what about the pronotum and wing pads?  Are they bordered by bristles?

For sure.  (You can also see the "lines" at the back of the head in this photo.)  So, a new small winter genus -- Paracapnia -- and we can go further.  These are Paracapnia angulata nymphs, since according to Beaty, "Paracapnia angulata is the only species of Paracapnia in the southeastern United States." ("The Plecoptera of North Carolina," p.1)  He also notes that this species is only found in the mountains.

And that's where we were this morning -- back in Sugar Hollow in the Blue Ridge, exploring yet another stream that empties into the Moormans.   It was a beauty.  And now for some more of the beautiful insects we found in this little stream.

1. Another Limnephilid caddsfly larva (Northern Case-maker) -- genus Pycnopsyche -- and again it had made the "three-sided" case out of pieces of leaves.  Interesting point on this type of case: Thomas Ames notes, I noticed last night, that this type of case is typical of early instar larvae.  "Immature larvae that build cases of leaves or other flimsy stuff usually convert them to sturdy rock and twig cases in the final instar." (Caddisflies: A Guide to Eastern Species for Anglers and Other Naturalists, p. 254.)  (For some of the Limnephilid cases that I found last summer, see the entry posted on 9/25.)  This larva made a beautiful case, and in one of the photos, you can see its head right at the edge of the case.

2. A couple of lovely Lepidostomatids.   I actually found quite a few.  Look for them in the leaf packs.

3. A fairly large Ameletid mayfly.  (Lots of them in this stream.)

4. One of many Epeorus pleuralis flatheaded mayflies that was crawling around on the bottoms of rocks.

5. A Peltoperlid (Roach-like stonefly).  These too are common in these small streams in Sugar Hollow.

6. Large winter stonefly: Taenionema atlanticum.

7. And a Chloroperlid (Green) stonefly that had just recently molted.  I couldn't tell what it was until I took a look with the microscope.  But, it was actually the largest Chloroperlid I've seen so far this season. (Genus Sweltsa: note the short tails, the shape of the wing pads, and the very hairy body -- especially the wing pads.)


Saturday, January 28, 2012

Malirekus hastatus in Our Own Backyard

So, last week I drove up to the Rapidan River in Madison county and found -- for the very first time -- the Perlodid stonefly, Malirekus hastatus, and today I found two of them in one of the tribs I study in Sugar Hollow.  No need to go far from home to find quality insects -- just head for the Blue Ridge Mountains.

Some more photos:


Since I posted the 1/21 entry on Malirekus hastatus, I've learned two things about this Perlodid.  1) Malirekus hastatus nymphs and Malirekus iroquois nymphs look exactly the same, but M. hastatus has submental gills; M. iroquois does not.  M. hastatus is found in the southeast; M. iroquois in New England and the mid-atlantic.  So, I guess we now know for sure that central Virginia's in the south!  Joking aside, the precise dividing line between the two species is not known for sure, so maybe we've discovered something important.  2) The second thing I've learned about M. hastatus nymphs is that they're very aggressive!  I collected a number of flatheaded mayflies this morning, Epeorus pleuralis, and made the mistake of putting them in the same bowl with my Perlodids.  When I next looked, both of my M. hastatus nymphs had Epeorus nymphs in their mouths!  And, when I was taking my photos, the M. hastatus nymph was constantly chasing an I. similis nymph around the side of the dish.  Happy to say, the I. similis always escaped.

Close call!

Important diagnostic features for M. hastatus, again, are the pale dots on the head that are anterolateral to the rear ocelli, the pale area that forms the ocellar triangle, and the "conical-shaped," tiny, submental gills.

Other nice findings today --

1. Lots of Isoperla similis nymphs -- much smaller in size that M. hastatus.  And note the different head pattern: no pale area in the ocellar triangle, and there are pale "spaces" that are anterolateral to the ocelli, but they're not in the shape of ovals.

2. A real surprise -- a Gomphid (Clubtailed dragonfly), genus Ophiogomphus, with wing pads that make it look fairly mature!  It was 14mm long -- close to 3/4 of an inch.

3. And another surprise, I found three Limnephilid caddisfly larvae, genus Pycnopsyche, all three in the three-sided cases made out of pieces of leaves.  One was kind enough to venture out of its home.

4. And finally, a photo of one of the many flatheaded mayflies I found -- all Epeorus pleuralis (Quill Gordons to you flyfishermen).  Look for them on the bottoms of rocks.   On one large rock that I turned over, there must have been 15-20 nymphs that scurried for cover.

Friday, January 27, 2012

Rapidan Riches: The Uncommon Taxa

I feel like I've spent most of the winter so far either waiting for sun, or waiting for the rivers to clear.
Today, we have blue sky and sunshine, but after rain overnight and a downpour this morning our rivers look like chocolate milk.  So, let me post a set of photos that I've been compiling.

I sample the Rapidan River in Madison county right where it flows out of the Shenandoah National Park.
It's a special stream, and I'll tell you why: I've found taxa there -- stonefly nymphs, mayfly nymphs, and caddisfly larvae -- that I've seen nowhere else in all of the streams I explore.  (The same is true for the tributaries to the Moormans River --  which are headwater streams -- and one of these days I'll write about them.)  So, let me go through the list of these "uncommon taxa," showing some photos, and noting the tolerance values for each taxon as posted in the recent list of tolerance values put out by the North Carolina Department of Water Quality (available on their website).

1. The Common stonefly (Perlidae), Paraganetina immarginata.  That's what's pictured in the photo at the top of the page, and I think it's one of the most spectacular insects, in colors and patterns, that I've yet to see.  Tolerance value: 1.1.  Another picture:

2. The Perlodid stonefly (Perlodidae), Isoperla nr. holochlora (i.e. it's "close/near" to I. holochlora, but not quite the same).  Tolerance value: 0.0.  Two photos:


3. The Perlodid stonefly, genus Yugus (arinus?  bulbosus?).  Tolerance value: not enough specimens found to determine a tolerance value (i.e. it's seen only rarely).   To date, I've only seen one.

4. The Perlodid stonefly, Isogenoides hansoni.  Tolerance value: not enough specimens found to determine a tolerance value.  I have only found immature samples so far: I hope to find a mature one so we can see it in its full colors.


5. The Perlodid stonefly Malirekus hastatus.  Tolerance value: 1.1.  This specimen is also immature.

6. The Spiny crawler (Ephemerellidae) mayfly, Ephemerella subvaria.  Tolerance value: not enough specimens to determine a tolerance value.  Perhaps the most colorful aquatic insect I've seen.


7. The Pronggilled mayfly (Leptophlebiidae), genus Habrophlebia.  Tolerance value: the only species listed is Habrophlebia vibrans, 0.3.

8. The Northern Case-maker larva (Limnephilidae), genus Pycnopsyche.  This is a genus I have seen elsewhere -- but only in a few, tiny, very good streams.  Pycnopsyche Limnephilids build cases that vary: each is unique.  Tolerance value of Pycnopsyche larvae in general is: 2.5.  Here are the two that I've found in this stream.

and, the "hot dog" case

9. And the other caddisfly larva that I've found in this stream that is truly "uncommon" is the Fingernet caddisfly genus, Dolophilodes.  Again, I have found this genus in a few other streams, but not very many.
Tolerance value for this genus: 1.0.


10. Since I've moved into the area of "seen elsewhere, but only a couple of times," let me add a final taxon:  the Giant stonefly, Pteronarcys biloba.  Tolerance value: 0.0.  The "hooked" corners at the front of the pronotum help us to ID this species.


It is very exciting to me, to find and photograph these kinds of insects -- exciting to find the "new" and the "uncommon."  (And note the very low tolerance values.)   Every time I get close to my "spots" on the Rapidan River, I tingle in anticipation -- "What will I find today?"

Saturday, January 21, 2012

Malirekus hastatus: A New Perlodid Found at the Rapidan

I hang my head in shame, since I once again -- in my posting of 1/18 -- identified an insect before I carefully checked the ID with my microscope.  The Perlodid stonefly in the photo above, which I found at the Rapidan River on Wednesday, is not Isogenoides hansoni -- it's Malirekus hastatus, a Perlodid that I've not seen before.

The first clue that I was wrong with the Isogenoides ID came when I looked at the mesosternal ridge.
This is what that looks like on an Isogenoides nymph, where median ridge of the "Y" intersects the transverse ridge at the top--

Here is the ridge of our Rapidan nymph.

No median ridge, no transverse ridge.  Oh dear.  So, let's start our quest for genus ID with Barbara Peckarsky,, Freshwater Macroinvertebrates of Northeastern North America (p. 71).  And we begin with couplet 37.

37a. Submental gills at least twice as long as greatest width...38
37b. Submental gills less than twice as long as greatest width, or absent...40

I did not see any submental gills when I first looked at the chin.  But, that led me nowhere, so I looked a little bit closer, and

sure enough there they were, I've just never seen gills that short and that wide at the base.  That means, by the way, that we opt for 37b. in the couplet and move on to 40.

40a. Lacinia of maxilla terminating in a single tooth lacking spinules or hairs on the mesal margin...Remenus
40b. Lacinia with a shorter spine mesal to major spine and commonly with additional spinules or hairs...41


On to 41.

41a. Lacinia with a sharp angle just below second, smaller tooth sometimes in the form of a knob with tufts or spinules of hairs...42
41b. Lacinia without a knob...43

There is indeed a "knob" below the smaller tooth and it does have tufts of hairs on it.  So we go on to 42.

42a. Submental gills present; outer ventral lacinial surface with basal patch of about 50 dark clothing hairs...Malirekus
42b. Submental gills absent or greatly reduced; ventral lacinial surface without dark clothing hairs, but may have smaller patch of setae...42.5

Here's a close-up of the ventral lacinial surface.

This is a tough call, since I can't really tell if there are 50 hairs on the surface, but, since the option of 42.5 leads us to a choice between Yugus and Diura -- neither of which match the nymph in our picture -- I would tentatively conclude that this is a Malirekus.  (For pictures of a Yugus nymph, see the entry for 3/25/11.  The body is bright yellow.  And, Diura is primarily a Western Perlodid genus.)

But, let's seek confirmation from two other sources, beginning with Steven Beaty's description of Malirekus in "The Plecoptera of North Carolina," p. 26.

Genus diagnosis: Nymphs 15-19mm [this one was 15mm, fairly large]; conical submental gills [great description!]; triangular lacinia with low marginal knob bearing a tuft of setae and ventral surface with a cluster of approximately 50 clothing hairs near base; single curved row of spinules on back of head, obsolete [i.e. missing] near midline.

In his "Notes," he adds some things that are important to us.  "Malirekus hastatus is the only species to occur in the southeastern United States.  Separate Malirekus from Yugus by the single row of spinules on the occiput.  The patch of clothing hairs on the lacinia a traditional diagnostic feature for separation of these two genera, may be difficult to see (setae can be dark or clear) or is not always present as the hairs can fall off."

So, we should not be overly concerned about not finding "50" clothing hairs on the ventral surface of the lacinia, and, we should be able to see a "single row of spinules on the occiput" (i.e. the back of the head).
And there is a row spinules with a gap in the middle.

I think the Malirekus ID is pretty secure, and "conical submental gills" describes the gills on our nymph perfectly.

But, let's check in one final source, Stewart and Stark's Nymphs of North American Stonefly Genera (Plecoptera), pp. 416-417 (Malirekus hastatus is illustrated on 417).   Here we find a more complete description than we've found so far of the body and head.

"Nymph Morphology: Body brown with dark brown markings; antennae, legs, cerci light brown.  Head mostly brown with light M mark forward of anterior ocellus; two pale, ovate spots lateral to ocellar triangle, and pale interocellar spot; two large ovate occipital spots, broken by reticulate brown lines and bordered behind by row of short, blunt setae."

Let's take a close look at the head, remembering that we've already seen the "row of short blunt setae" at the back of the head in the previous picture.

Perfect!  That's enough for me -- I no longer have doubts.   This nymph is genus Malirekus, and, following Steven Beaty, Malirekus hastatus.   The Rapidan is a river that's rich in Perlodids.  I've now found the following: Isogenoides hansoni, Yugus, Malirekus hastatus, Helopicus subvarians, Isoperla namata, Isoperla holochlora, and Isoperla nr. holochlora.   Will I find something new on my next trip?
That would be great!