Tuesday, May 16, 2017

The free-living caddisfly larva Rhyacophila carolina -- or so it seems


Out to Sugar Hollow this morning hoping to find our as yet unidentified Isoperla stonefly -- I. sp. VA.  We found some, but they were still very small.   Not sure we'll find the mature nymphs and/or adults until well into June.  But there was this free-living caddsfly larva of interest.

A quick review of the Rhyacophilids we've found so far in the small streams that we explore.

1. R. fuscula -- a very distinctive green with a very distinctive head pattern.


2. R. nigrita -- dark front edge on the pronotum.


3. R. banksi complex


4. R. glaberrima -- this is the only one that I've seen so far.


and 5. R. carolina  -- one that seems to show up in late spring.  (I see those above throughout the winter starting in December.)


I've seen one other Rhyacophila, but it seems to occur in a different habitat -- I've not seen it in Sugar Hollow.   I've found it two times, once in the Doyles River, the other time in the Lynch.  Rhyacophila ledra.  (R. ledra, like R. carolina, is in the "R. carolina group".)



Let's look again at R. carolina.  There are two distinctive features: 1) the head is golden brown (Beaty, "The Trichoptera of North Carolina," p. 60), and 2) there are no ventral teeth on the anal claw.  The claw look like this.


And the heads on the larvae I've found are indeed golden brown.  (Also note that the head is rounded laterally and narrows anteriorly.) Two more examples.



Notice too that there are no markings on the head -- it's uni-color.

Now back to the larva that I found this morning.  The anal claw is a match for R. carolina.


And the head is golden brown, but...


There is a very distinct dark medial line both on the head and the pronotum.  Hmm....  What I'd like to know is -- is this a common variant with R. carolina?  Or, is it something unique to our streams in Sugar Hollow?  Time to contact Steve Beaty.

(There is, by the way, another species in the R. carolina group -- R. teddyi -- but that larva remains undescribed.)


Tuesday, May 2, 2017

Nice photos today from Buck Mt. Creek


We needed the rain -- and we got it!  The down side is that now our streams are high and finding the insects isn't that easy.  Still, today when I could find a wad of decomposed leaves I could find nymphs.  And the light was just right for some good photos.
________________


1. Spiny crawler mayfly, Drunella tuberculata.   I seem to find one every year in Buck Mt. Creek, though Beaty notes these nymphs as being "uncommon."  ("The Ephemeroptera of North Carolina," p. 48)  Drunella nymphs can be identified by their muscular fore femora, on the leading edge of which there is a uneven row of tubercles.  You can sort of see them in this photo,


but they're much clearer in this microscope photo of Drunella cornutella.


The key feature for the species ID is the pair of tubercles on the occiput.  These.


I got a great pic of these several years ago when I got a nymph to look directly into the camera.


But that was a real beauty today.



2. A small minnow mayfly, Beatis intercalaris.


This is one of our "summer" Baetidae.  It's fairly common fairly, and it's easy for us to make the ID.  1) Note how the cercal segments (tails) are banded -- at the base, in the middle, and at the tips.


And note the pale "parentheses" ( ) marks medially on each of the terga.  (Clearly visible in the first photo.)

________________

3. Flatheaded mayfly, Leucrocuta sp. (hebe?).


Leucrocuta is distinguished from genus Heptagenia by the lack of fibrilliform at the base of gill number 7.


Beaty cautions to leave Leucrocuta nymphs at the level of genus.  However, most sources seem to agree that the pale markings on terga 4-5 and 7-8 are indicative of L. hebe.
________________

4. Number 4, the flatheaded mayfly, Maccaffertium modestum.  Very pretty caramel color.



This is one type of M. modestum -- fairly uniform in color with fairly plain femora.  The other -- this one --


is darker in color with femora that are heavily marked.  Both types are found in Buck Mt. Creek.
________________

Up to the Rapidan River this weekend.  Sure hope the water keeps dropping.

Saturday, April 22, 2017

Project for a rainy day: re-examining Amphinemura species ID


Rain at last, and it's supposed to continue through Tuesday.  Our streams really need it.

You'll recall that I found quite a few Amphinemura Nemourids last week at Buck Mt. Creek.  On Tuesday, I went to the Rivanna and they were in there as well.


Some time ago I worked on Amphinemura species ID and reached the conclusion that those that I've found in our streams are Amphinemura delosa.    This was based on the description of A. delosa found in a 1971 article by P. P. Harper and H. B. N. Hynes: "The nymphs of the Nemouridae of Eastern Canada (Insecta: Plecoptera)," Canadian Journal of Zoology, 49: 1129-1142.  Let me review their description (their words cited in BOLD) noting those features on the nymphs that I've found this week and last.  (See p.1131 of their article.)

1. Total length of mature nymph, 5-6 mm.  The nymphs that I found were all 5.

2.  Color medium to dark brown, head darker; antennae pale, first few segments darker; Yes.


3. legs brown; ... cerci pale, first few segments darker;  Yes.


4. Short bristles covering head capsule, those behind eyes longer and stout.  Very clear.


5. Pronotum rectangular, nearly as broad as head, covered with short bristles and hairs; pronotal fringe well defined, consisting of long pointed bristles.  They are indeed long and pointed.  Not real easy to see the bristles and hairs on the pronotum itself with all of the sand and silt on the nymph.


6. legs with long stout bristles, the longest femoral bristles longer than the greatest width of the femur.  They don't seem quite that long on my nymph, but I think they're close enough.  This nymph was still immature.


7. a few long hairs on the tibiae but no tibial fringe.  Yes.


8. prosternal gills in four tufts; distance between the median tufts about twice that between the median and lateral tufts; each tuft comprising about eight (in mature nymphs) filaments forming a whorl around a central axis.    That's a match for our nymph.


9. Finally, abdomen covered with long bristles, the longest marginal bristle longer than the mid-dorsal length of the corresponding tergum.


___________________

Looks like a slam dunk to me.  But just to be sure, I thought I'd see what Steve Beaty says in his latest work on "The Plecoptera of North Carolina" (Version 4.0, 2015).  Gives me pause.

To begin with, he notes that four species of Amphinemura have been found in North Carolina: appalachia, delosa, nigritta, and wui.  (Harper and Hynes, by the way, have described A. nigritta and A. wui but not A. appalachia. A. delosa and A. nigritta are very similar, but not exactly the same.)  But he cautions those of us using his guide to leave Amphinemura ID at the level of genus.  I'm not exactly sure why -- I need to check in with him on this matter.  I suspect he feels that we need to be cautious until the nymphs of all four species have been fully described.  Then again, he may question the reliability of a study done nearly 50 years ago.  There is good news: B.P. Stark (of Stewart and Stark) is apparently preparing a "nymphal key to the eastern species of Amphinemura," but it will not include a description of A. appalachia.  Bummer.

All things considered, I think that at the moment the safe thing to call the nymphs I've been finding is Amphinemura sp. (delosa?).  I'll let you know if that changes.
_____________


Saturday, April 15, 2017

Isoperla davisi at Buck Mt. Creek


A species of Isoperla that I haven't seen for four years -- Isoperla davisi -- one that I've only seen at Buck Mt. Creek.   Better review how we arrive at the species ID.


We rely on the patterns we see on the abdomen and the head.  "pre-emergent nymphs 7.0-8.0 [mm].  Lacinia recedes from base with 6-8 stout marginal spines below subapical tooth; both pale area anterior to median ocellus and pale ocellar spot enclosed; transverse brown bar on anterior frontoclypeus wider than brown area that encloses the anterior pale median area." (Steve Beaty, "The Plecoptera of North Carolina," p. 59)

Our nymph is 8 mm long.  The lacinia is as described,


as is the head pattern.


Beaty continues: "dorsum of abdomen with distinctive longitudinal '5-lined' banding; median and sublateral bands darker and usually narrower than submedial bands and with intervening pale narrow lines."  



If you go to NatureServe Explorer (http://explorer.natureserve.org/) and enter "Isoperla davisi," you'll see that the common name for this species is "Alabama stripetail."  Curiously, they fail to note that this species is found in both Virginia and North Carolina (here only listed for Alabama, Florida, and South Carolina.)

Good to see this one again.



_________________

It was a great day at Buck Mt. Creek.  Lots of insects around, including a bunch of Nemourids, the genus we see in the Spring -- Amphinemura.  (Amphinemura delosa.)



These are the Nemourids with the "cervical gills," which makes them very distinctive.

_________________

I saw a lot of Amphinemura, but without any question, the bug of the day in terms of sheer numbers was the small minnow mayfly, Plauditus dubius.   I saw both male and female, and almost every nymph that I saw had black wing pads = ready to hatch.





They can be distinguished by gender with a quick look at the eyes -- big eyes on the males (first photo) -- but the abdominal patterns differ as well.  While the pattern is hard to see on our male since it's so black, we can see the key feature on the female.  "female -- median spots on terga 2 and 6."  (Beaty, "The Ephemeroptera of North Carolina," p. 22)


The dark median band on the tails is present on both male and female.
_________________

The weather's been great so I hope to get out a lot more.   The warm temps and low water we've had most of the year, mean that things are ahead of where we expect them to be.  To wit, I'm already finding Isoperla holochlora nymphs.  Very early.