Friday, November 25, 2011

Back to Work on the Freeliving Caddisfly Larvae

I went back to the Moormans today -- well, back to one of the small streams that feeds into the Moormans -- where I found, among other things, this immature freeliving caddisfly larva.  A lot of freeliving caddisfly larvae inhabit this stream, and I've written about them before and posted photos.  To refresh your memory, look back at the entries from March 4th, May 20th, and June 14th.  The colors have varied: some were bright green, some were aquamarine, some light green, and some were a nice creamy white -- like the one in the photo below (this was shot on March 4th.)  (Of all of the photos I've taken this year, by the way, this is probably my personal favorite.)

The most common freeliving caddis we see in our streams is bright green, with a distinct pattern on top of its head.  This one.

This is the insect monitors expect to see if they see a freeliving caddis.  This larva is a Rhyacophila fuscula.  Let's see what Beaty has to say on this species:
"R. fuscula -- larvae large, ?? mm; long apicolateral spur; dark H-pattern on head interrupted anteriorly and extended posterolaterally; pronotum mostly dark.  Most common and tolerant Rhyacophila in NC."
("The Trichoptera of North Carolina")  (The tolerance value is still a mere 1.6.)

So what is the "apicolateral spur," and can we get a better look at that "H" on the head?  The "apicolateral spur" is a spur that sticks out from the top (apex) of the anal proleg and parallels the anal claw.  This is easy to see in a microscope photo.

The "interrupted H pattern" can be seen in the photo above, but it shows up better in this photo I took at the start of the month (November 4th, Rapidan River).

So, there is no top (front) to the "H," but the dark colors extend to the side and the rear.  Rhyacophila fuscula.

But what about the larva that I found today?   Clearly not Rhyacophila fuscula -- but it is a Rhyacophilid (freeliving caddisfly larva)!  Here's another look at the larva, and take a look at that head and pronotum.

The head is burnt orange to brown to almost black at the front -- no "H" pattern in sight.  And the body will not be bright green when the larva matures: I'd go for creamy white or aquamarine.

Does it have an "apicolateral spur" on the anal proleg?  It does not, though there do seem to be "ventral teeth" on the anal claw.  Take a look.

The "ventral teeth" seem to eliminate what might otherwise be a possible option -- R. carolina -- about which Beaty says: "R. carolina -- larva ?? mm; head golden brown.  Second most common Rhyacophila in NC."

At the moment, I'm leaning towards R. nigrita (TV is 0.0), which lacks the apicolateral spur but does have ventral teeth on the claw.  And there's another relevant feature -- the color of the pronotum.

"R. nigrita -- larva ?? mm; head black or brown and parallel sided; pronotum darker anteriorly.  Occurs mostly in small Mountain streams.  Third most common Rhyacophila in NC. "  Take another look at the head and the pronotum.

The front edge of the pronotum is clearly darker than the rear portion.  Species ID of Rhyacophila larvae will be an interest of mine throughout the winter and spring.


My other findings today were things that I would have expected: Giant stoneflies, Common stoneflies (Acroneuria abnormis and Eccoptura xanthenses), crane fly larvae (still pretty small in this stream), Peltoperlid (Roach-like) stoneflies, a few flatheaded mayflies, and, of course, lots of small winter (Capniid) and green (Chloroperlid) stoneflies.  Here are some photos of the latter taxa to finish the entry.

Small winters:


And a "double":

(Below, one of the riffles I sampled today.    I go looking for aquatic insects for the same reason that I go fishing for trout -- they live in beautiful places.)

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