Wednesday, February 25, 2015

Snowed in and frozen out -- and we're missing so many nice things


Twenty inches of snow in one week, with morning temps in the single digits and teens: February in a nutshell, this February at least.  So with the sun out this morning and more snow and cold on the way, can you blame me for trying to get out to a stream?  Alas, you can see what I found when I got to Buck Mt. Creek: I needed my ice skates instead of my boots!

The problem is we're missing a lot of beautiful insects that are close to, or already fully, mature.  E.g. just look what I've seen in previous years at this time.  A sampler.

1. Giant stoneflies

Pteronarcys biloba (Rapidan River): 2/17/12


Pteronarcys proteus (Sugar Hollow): 2/13/12


2. Perlodid stoneflies

Helopicus subvarians (Buck Mt. Creek): 2/6/12


Clioperla clio (Buck Mt. Creek): 2/17/12


Malirekus hastatus (Sugar Hollow): 2/13/12


Isoperla similis (Rapdian River): 2/24/14


3. Nemourid stoneflies

Prostoia completa (Buck Mt. Creek): 3/1/11



4. Large winter stoneflies

Taenionema atlanticum (Sugar Hollow): 2/2/12


Strophopteryx fasciata (Buck Mt. Creek): 2/6/12


4. Small winter stonefly

Paracapnia angulata (Sugar Hollow): 1/30/12



5. Small minnow mayflies

Heterocloen amplum (Doyles River): 2/6/12


Heterocloen amplum (Doyles River): 2/17/13


and Baetis tricaudatus (Rapidan River): 1/18/12


Baetis tricaudatus (Rapidan River): 2/24/12


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What a pity.  Let's hope for warm weather and sunshine in March -- which starts on Sunday!  Until then, the "treasure hunt" is on hold.

Saturday, February 7, 2015

The small winter stonefly Paracapnia angulata: going higher in Sugar Hollow


A beautiful spot: higher up than I've gone on this stream before.

I worked hard today to locate new things, digging into the substrate, but most of the insects I've seen here before.  One exception:  the small winter stonefly, Paracapnia angulata.


We've found them before on the other side of the valley (see, for example, 1/30/12), but further down in this stream, I've seen nothing but the more common small winter, genus Allocapnia.  The main difference, you may recall, at least in making a real quick ID -- the shape of the rear wing pads.  On Allocapnia nymphs, the posterior edge of the rear wing pads is truncate (flat),


on Paracapnia nymphs, they're more rounded off.


Today is the first time that I've noted the "parentheses" on the terga -- they showed clearly on segments 4-7 -- but when I looked at my photos from previous years, I could see them on the live nymphs as well.  (Visible on terga 2-8)


While Allocapnia nymphs have a tolerance value of 3.3 (North Carolina values), Paracapnia angulata hasn't been rated.  That normally means it's not seen that often.  Habitat?  "Nymphs typically occur in small headwater streams, possibly in leaf packs."  (Beaty, "The Plecoptera of North Carolina," p. 1)  That's affirmative.

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A few other findings -- photos that turned out alright.

1. Perlodid stonefly, Isoperla similis.  Not uncommon in these headwater streams, but overall not very common.


2. Uenoidae, Neophylax mitchelli, tolerance value of 0.0.


This one has clavate ventral gills and a sharp tubercle on its head (visible in this photo), one that tends to point to the rear.  Also, light colored legs and normally a light colored face, and 1-3 setae in the ventral sa3 position.


Not the best photo -- but good enough.


3. Roach-like stonefly, genus Tallaperla.  Keep looking for the species that has only one gill sticking out behind the rear wingpads (Viehoperla ada): still haven't found one.


Friday, January 30, 2015

Cabin fever sets in -- time to get to a stream


The wind and cold couldn't stop me this morning.  With no warm weather in sight, I decided to brave it and check out a small stream in Sugar Hollow.

I was hoping to find two different things, and I found both.  That's one in the photo at the top of the page: the free-living caddisfly larva, Rhyacophila banksi complex.


I've found this species before in this stream, along with R. fuscula, R. nigrita, R. glaberrima and R. carolina.  This is the best stream I know of for finding Rhyacophilids.    This larva matches the description for the species R. banksi, but entomologists feel R. banksi can't be distinguished from a number of similar species.  Hence, "R. banksi complex" (which belongs to the R. invaria group).


On January 28 of last year, I posted a thorough review of how we arrive at this identification.  There's no need to go over that detail again.  But, two of the features that nail this down are

1) There is a single, large, ventral tooth on the anal claw,


and 2) the second segment of the maxillary palp is twice as long as the first.



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My second goal was to find one of those Isoperlas that I think might be I. kirchneri (see the entry of 1/25) -- and I was successful.


Whatever species it turns out to be -- I. montana, I. kirchneri, or something else -- this is the same nymph that I've found here in previous years: no "bars" or "stripes" behind the ecdysial suture.


Since I had none of these in my collection, I preserved it so I could see what the lacinia looked like.  But, nothing unusual there: same shape and make up that we normally see on most Isoperlas.


This was a young one.  Have to get back here in March and April to see one that's mature.

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The most common taxon today?  Not much question about it: the large winter stonefly, Taenionema atlanticum -- and this one was fairly mature.




Wednesday, January 28, 2015

The importance of laciniae in Perlodid stonefly genus ID: focus, Isoperlas


(Perlodid stonefly, genus Skwala.  Oregon, October, 2013.)

For those of you who, like me, like to work at the level of genus ID, with Perlodid stoneflies, one of the first things you need to examine is the laciniae ("teeth" used for tearing) of your nymph -- shape and constitution.  If you look at the keys -- Peckarsky's Freshwater Macroinvertebrates of Northeastern North America; Merritt, Cummins, and Berg, Aquatic Insects of North America --  you'll see that laciniae can differ markedly.

For example, each lacinia of the genus Remenus has only one tooth.



Diploperlas have two (apical and subapical).



The laciniae of Malirekus stones are more elaborate: two teeth, a knob with a tuft of setae, and dark clothing hairs along the base.


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In general, the shape and make-up of the lacinia can help us get to the level of genus when we're working through keys.  But Isoperla Perlodids can present a bit of a problem.   Here is the lacinia of Isoperla dicala which represents very well the general Isoperla description we find in the keys.


There is an apical tooth and a subapical tooth; the base is wider than the apex; below the subapical tooth, there are usually 4-6 spine-like setae with finer setae often continuing on to the base.  And, Isoperla laciniae are often medially constricted.

Here is the description we find in Merritt, Cummins and Berg, p. 332.

88' Apical lacinial tooth much shorter than rest of lacinia

89  Inner lacinial margin with row of at least 4-5 long seta; no prominent knob bearing pegs below subapical lacinial tooth....Isoperla  (Remember that Malirekus has that "prominent knob.")

And in Peckarsky (p.71)

41b. Lacinia without a knob, rounded or tapering from the smaller spine to base


 Beaty's description is more detailed ("The Plecoptera of North Carolina," p. 23)

Lacinia bidentate with apical tooth shorter than rest of lacinia and typically without low rounded knob; lacinial margin with row or tuft of at least 4-5 long setae, some species with row approaching base."

This description holds true for almost all of the Isoperla species I've found.  This lacinia -- along with the longitudinal abdominal bands -- will help you ID the following species: Isoperla dicala, Isoperla holochlora, Isoperla nr. holochlora (which actually lacks the longitudinal bands), Isoperla montana/kirchneri, Isoperla similis, and Isoperla davisi.  But there are some exceptions that need to noted.

1. Isoperla orata.  



The apical tooth of the lacinia is very long, as long as the rest of the lacinia.  And there is a bit of a knob below the subapical tooth on which we find exactly 3 setae.


2.  A second exception -- the nymph I've been calling Isoperla nr. orata -- in part because the laciniae are so much alike.


The lacinia differs in one important way: there appear to be 5-6 setae on the knob below the subapical tooth.


3. And for the strangest one I've seen so far, Isoperla lata.


This lacinia looks nothing like the other Isoperlas we've seen.  



Beaty's description - "lacinia distinct, broad, apex as wide as base and covered with a dense brush of setae."  Wierd, and it looks like there's only one tooth.
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I guess the point to be made is use your keys with caution: they don't always get you to the right place.  And with Isoperlas, I'd encourage you to go right to Beaty's descriptions.  Remember that his "The Plecoptera of North Carolina" is available on line.  You can download it and print it.  Go to:
http://portal.ncdenr.org/web/wq/taxonmanual.
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Isoperla nr. holochlora.  An Isoperla species on which the longitudinal stripes on the abdomen -- usually three dark bands against a lighter background -- are indistinct.