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.)

No comments:

Post a Comment