Monday, June 20, 2016

Sticking to photos today: got some good ones at the Rapidan River

I don't normally take photos of this one since I took a lot of them early on.  But, what a chubby!  I used to work with a gal who called this larva "Michelin man" -- seems pretty fitting.  Caddisfly larva, Rhyacophila fuscula.   I'm seeing a lot of big ones at the moment.


And I believe I mentioned last time that I find quite a few Paragnetina immarginata at the Rapidan River.  One of my photos is great for species ID.  I'll add it later on if I can get this damn Photos software to work!  (Hope my computer isn't on its last legs.)

Made the mistake of putting two in my tray at once, and I couldn't keep them apart.

And I found another Rhithrogena.   This one was fully mature and given the spreading, rising wing pads,  I'm pretty sure it was in the process of hatching.

You'll recall that we first saw this nymph at the Rapidan on May 25.  At the moment, Rhithrogena sp., possibly R. manifesta.


Also found a few little Perlesta.  I'll do some microscope work on this one and see how it compares to the nymphs I've found in other streams.

I'll edit this entry if I mange to annotate the picture I mentioned, pointing out the key features for species ID for Paragnetina immarginata.

Here we go.  Beaty, "The Plecoptera of North Carolina," p. 18.  "head M-pattern with medial pale line extended anteriorly, often connected to pale frontoclypeal margin; yellow femora distinctively patterned with dark brown longitudinal bar extending about 2-3 the length; abdominal terga banded, anterior half dark; anal gills absent."

Sunday, June 19, 2016

A Drunella double at Entry Run: cornutella and tuberculata

But first things first.  A beautiful, fairly mature, common stonefly, Paragnetina immarginata.  Think I've found one in Entry Run before but they're more common in the Rapidan River.  TV 1.1.

Drunella spiny crawlers.  Today I found both D. cornutella and D. tuberculata.  Drunella seems to be the only spiny around at the moment.  The more common Ephemerella nymphs have already hatched. Drunella nymphs are by far less tolerant of stream impairment.  The tolerance value of both of our species -- cornutella and tuberculata -- is 0.0.

Drunella cornutella.  I found a bunch of them today, but then Beaty says they are "common."  ("The Ephemeroptera of North Carolina," p. 25)  They're fairly small.  This one was 6 mm.

Distinguishing features?  Two things stand out: "head smooth with moderately long lateral frontoclypeal projections but less than half as long as the distance between them; median ocellar tubercle blunt to moderately sharp."  Yep.


Drunella tuberculata.  Less common than cornutella and somewhat bigger (this one was 8-9 mm).   Key features for the ID of this species are, in addition to the fact that it lacks the lateral frontoclypeal projections, "head with long occipital tubercles not divergent apically ... abdomen with paired dorsal tubercles always well developed on segments 5-7."  (Beaty, p. 25)  You can see the occipital tubercles on the nymph in the photo above, but this microscope photo is better.

Abdominal tubercles as you can see are present on terga 3-8 and definitely prominent on 4-7.

Drunellas apparently hatch as "Eastern Blue-winged Olives" for us fly fishermen.  I can't imagine that's is a "blizzard" out there when they do!  But they'll be big.  You can probably get away with a size 14 hook, maybe even a 12.

Providing much better hatches of BWO's are the Baetidaes -- small minnow mayflies -- and we see a lot of them in the summer, and a lot of different species.  Today I found one of my favorites: Acentrella nadineae.

This one was fully mature, in fact, I think it hatched while I was taking photos of other insects.  In any event it was not in my bowl when I went to release it -- and there was a shuck floating on top of the water!  You may recall that this happened to me before.    9/16/14, Rapidan River.

Olive body, bluish gray wings.

Two things help us with this species ID.  First look at the gills.  "gills elongate asymmetrical, and with basomedial pigmentation splotches."  (Beaty, "The Ephemeroptera of North Carolina," p.4)

And second, "distinct abdominal color pattern often tinged with red." (Beaty, p.4)  While we can see that on this nymph, it is much clearer on a nymph that is not this mature (and therefore not so dark).


I'm seeing fewer and fewer insects now in our small mountain streams.  Time to get down to the Rivanna.

Monday, June 13, 2016

Tiny crayfish -- couldn't resist!

What a cutie.  Not something I normally photograph, but the colors drew my attention.  I've been seeing a lot of crayfish lately, but nothing this small.  I'd say this was 10-15 mm.  Doyles River.

Sunday, June 12, 2016

Perlesta nymphs: initial thoughts on making species distinctions

Please keep in mind that any observations I have at this time are provisional.  Beaty lists the names of 17 species that are found in North Carolina, noting that most are undescribed.  I'd better cite him: "North Carolina has very high diversity of Perlesta, most of which are currently undescribed in the immature stage.  While many nymphs appear highly freckled some nymphs have few or inconspicuous freckles.  ...  It is not uncommon to get 2-3 nymphal habitus forms at one site."
("The Plecoptera of North Carolina," p. 49 in the latest version -- 4.0, 2015)  He also notes that the famed entomologist Bill Stark will publish this year a Perlesta key, but he advises us not to use it "as it contains only 6 of the 17 regional species."

So, we can forget about attempting any species ID.  My goal this month is a simple one -- to identify features that appear to me as likely to related to species distinctions.  So far, I've noticed three.  They are: 1) the density and size of the "freckles" we see on a nymph (these black dots are the pigmentation at the base of the setae on this very setose taxon); 2) the color of the ocellar triangle, and 3) the nature of any anterior extension from the pale "M" on the head.

Thus, with the nymph at the top of the page -- one that I found in the Rivanna River in June, 2011 -- the freckles are dense and large.

On the head, the ocellar triangle is filled in and setose, the "M" pattern is interrupted, and there is no anterior extension.

I might also note that this nymph is unusally dark -- abdomen and head -- the darkest Perlesta I've seen.

For a nymph that appears totally different, let's look at the nymph I found in Sugar Hollow last week.

The abdomen is lightly freckled and the black dots appear to be small.

And on the head, the ocellar triangle is noticeably pale and devoid of setae, the "M" is well-defined, and there is a well defined anterior projection from the middle of the "M".

There is something else we can see on this nymph that may be important.  On terga 9 and 10, we can detect a faint, dark line laterally on those segments.  While that line here is indistinct, it is very clear on other Perlestas I've found.


Looking at those 3-4 traits, let's see what I've found in the Perlesta photos I've archived over the years.

I. nymphs that are densely freckled

1. Buck Mt. Creek, May 28th of this year

Very speckled and the dots are large.  And note the lateral abdominal lines -- they are visible on all of the tergites, curving inward on 8 and 9, then moving slightly back to the side on 10.

 On the head, the ocellar triangle is filled in with dark spots/setae, and it looks to me like the "M" extension absent.

2. Rivanna River, 7/8/14

Dramatically freckled.  No real "M" pattern visible though there is a pale space at the front of the head.  And, if you look closely, you can easily see the lateral, abdominal lines.

3. Lynch River, 6/6/12

and 4. Doyles River, 5/23/12, one that's fully mature


II.  Well defined anterior extension, freckles light

1. the nymphs that I'm finding in the small streams in Sugar Hollow, the one that we've posted above, and this one

2. from the Doyles River, 6/23/11 (though note that on this one, the ocellar triangle is filled in/setose.


III. anterior projection blurred or missing

1. Buck Mt. Creek, 6/11/16

Note the head.  Not sure we can call that an "M" since the middle broadly extends to the front of the head.

Again we can see the lateral abdominal lines.

2. Buck Mt. Creek, 6/3/11, one that's completely mature

3. another that was completely mature, 6/14/13, Doyles River

4. to this "type" we can add the nymph from the very top of the page.

Well, it's a beginning.  All I can do at this time is work to discern traits that might be significant in establishing species ID.  I may or may not have picked out critical things.  Hope that some day we'll know one way or the other.