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.