Thursday, December 1, 2016

Some beautiful insects at the Rapidan River this morning


Common stonefly, Agnetina capitata.  The light was just right for some good photos this morning, and I had some very good subjects.  I have yet to find this one anywhere else.  Described by Beaty ("The Plecoptera of North Carolina," vers. 4, p. 40):

Lateral arms of M-pattern on head directed laterally; dark area between lateral ocelli sometimes lighter to median ocellus; dorsum of abdomen banded, posterior margins dark and with a triangluar mesal area anteriorly projecting forming an apparent mid-dorsal longitudinal stripe; apex of tergum 10 light with dark pigmentation faintly continuous mesally, sometimes with a small median projection directed distally.

All good.


Just a very handsome stonefly.




And a nice side view as well.

_________________

And the other beauty I found -- actually, I found three of them -- was that very colorful spiny crawler, Ephemerella subvaria.




(Enlarge and note the detail on the head.  Ornately patterned.)

_________________

The leafpacks were full of two things today: pronggilled mayflies and small winter stones.  Took a couple of shots of the latter.  Allocapnia for sure for the genus: species -- probably pygmaea.



__________________

After a long, long dry spell it finally rained.  The collecting should start to improve.

Saturday, November 19, 2016

A few photos from the North Fork of the Moormans


The Moormans River begins at the base of the dam on the Sugar Hollow Reservoir.  Flowing into the lake are the North and South Forks.  The North Fork is a boulder-strewn, cold water stream that's popular with fly fishermen, and in it we find high quality insects.  Took these photos this morning.

1. Common stonefly, Acroneuria carolinensis (pictured above)




2. Common stonefly, Acroneuria abnormis


3.  The "strong casemaker" (Odontoceridae), Psilotreta labida


4. And the giant stonefly, Pteronarcys biloba, tolerance value -- 0.0




Oh, and clinging to our giant stonefly, the large winter stonefly, Taeniopteryx burksi


Friday, November 18, 2016

Corrections on the carolnensis/lycoria distinction


In reviewing additional photos of Acroneuria carolinensis last night, I noticed two things that differ from the points that I made yesterday.  1) On some specimens, the dark areas on the femora look just the same as those on Acroneuria lycorias.  I.e., they're extensive and extend from the proximal to the distal ends on the anterior edge.  And 2) the dark dots on the terga are anteromedial, not posteromedial, and reach back into the pale anterior band.


Thursday, November 17, 2016

Stoneflies at Buck Mt. Creek: one I was hoping to see and some that were fully expected


This is the one I was hoping to see: common stonefly (Perlidae), Acroneuria lycorias in part because I continue to work on distinguishing this species from Acroneuria carolinensis.  This is a problem I've noted before.  Entomologists think the two can be confused, and it's true that they look much the same.  Compare our nymph from today with the A. carolinensis nymph that we noted just 10 days ago.


Pretty darn close.  However, with A. lycorias nymphs "anal gills [are] usually present" (Beaty, "The Plecoptera of North Carolina," vers. 4.0, p. 38) while on A. carolinensis they're typically absent.  But according to Steven Beaty, this is not a hard and fast rule.  He says, "...the distribution maps for A. carolinensis and A. lycorias suggest that these two species have historically been confused with each other.  There are some populations of Acroneuira carolinesis that have either sparse anal gills, anal gills only on one paraproct, or missing the gills entirely (particularly smaller specimens)." (p. 38)

Obviously, the evidence I have isn't extensive.  Still, it has been consistent and I hope that others will consider the factors I've noted.  What I've found is that with the nymphs that lack anal gills, there are small, dark, posteromedial extensions on the terga, and the dark spots on the femora are restricted to the distal and proximal locations.  This.


Also, I've only found them in cold mountain streams (Upper Doyles River, Entry Run in Greene County,  Rapidan River).   By contrast, the nymphs that have anal gills 1) lack any posteromedial extensions, and 2) the spots on the femora are extensive and may even extend across the anterior edges.


This is a nymph that I have -- so far -- only found in Buck Mt. Creek (not in the mountains), but I'm sure it occurs elsewhere in other streams.

In the end, the only way to be sure that these distinctions are valid is to find some corresponding adults.  Not sure that's something I'll ever do.

More pics of this nymph from this morning.



_________________

What are the stoneflies I was expecting to see?  Small winters -- Allocapnia sp. (pretty sure they're all pygmaea).




Even saw one that was fully mature.



Unfortunately for this little nymph, our A. lycorias nymph saw it as well --


and inhaled it!


(Note the rear end and tails sticking out.)  Alas.

Sunday, November 13, 2016

Flatheads and Perlids -- that's about it at the moment


Yesterday, I hit the Rivanna at Crofton: today, it was a small stream in Sugar Hollow.  And, at both streams I found much the same thing: common stoneflies, Acroneuria abnormis in both cases, and flatheaded mayflies -- but not the same species.  In the photo above, the "brown" form on A. abnormis.  So, so broad, a very unusual shape.  But it made for some very good photos.


And the flatheads I found in the Rivanna were -- like those in Buck Mt. Creek -- Maccaffertium modestum.


_________________

Different habitat, different results.  In Sugar Hollow today, it was the "patterned" form of A. abnormis.




And the flatheads out there were Maccaffertium pudicum, a species with a much different tolerance value (2.1 vs. the 5.7 of M. modestum).



To be fair, I did find other insects.  I saw giant stones at both of the streams, P. dorsata at the Rivanna and P. proteus in Sugar Hollow.  And at the Rivanna, I found another Acroneuria arenosa/evoluta, the one with anal gills present.



And there were Goera larvae (weighted case-makers) in our small mountain stream.


But the story at the moment seems to be Acroneuria stones and Maccaffertium flatheads.  Things will be changing real soon.