Friday, August 15, 2014

Case-maker day at the Rapidan River

(Obviously "not" a case-maker caddisfly larva -- but still one of the prettiest common stoneflies we find: Paragnetina immarginata.  It's a small one.  Even so, it measured -- I'd guess -- about 20 mm.  The Rapidan is one of the few places I see them.)

It was another day when I expected to find lots of small minnow mayflies, and I did find a couple.  But of much greater interest, I found 5 different case-maker families: Goeridae (Goera calcarata), Limnephilidae (Pycnopsyche scabripennis), Brachycentridae (Brachycentrus appalachia), Odontoceridae (Psilotreta labida), and Glossosomatidae (Glossosoma nigrior).

1. Weighted-case maker, Goera calcarata

The Goerid was the first thing I found, not something I ever expected to see.

I thought it was a Glossosomatid (Saddle-case maker) until I dropped the case into my bowl.  The two large pebbles on either side of the case immediately gave it away: Goeridae, the "weighted-case maker."   I thought these showed up in late fall and winter -- thinking I have to revise.

A defining trait of Goera -- in addition to the conspicuous case -- the "pronotum [is] produced anterolaterally into wide, sharply pointed processes." (Beaty, "The Trichoptera of North Carolina," p. 87)  Easy to see in the first photo.

This appeared to be Goera calcarata.  It was about 8 mm long with 3 pairs of sclerites on the metanotum.  Also, I did not see any sternal thoracic plates (which are distinct on Goera fuscula -- see the entries posted on 10/27/13 and 11/27/13), and there were "conspicuous spicules" on the anterior edge of the pronotum.  (For all of these traits see Beaty.)

By the way, if you find one of these cases but don't see the larva, turn the case on its back.  This larva only emerged when its case was flipped over.


2. Northern case-maker, Pycnopsyche scabripennis

I usually see these in the spring, so this too appeared to me to be out of season.  But there it was.  This is a large larva: the case was 25 mm, the larva about 22.  Nothing special I thought -- until I got home and downloaded my photos.  Then I spotted what looked to me like a tiny case on the side of the case.

And it was!  Under the microscope, I peeled this little case off and pulled it apart, finding this inside.

It's a midge!  How about that.  Actually, there's a whole world of "micro" midges, and my friend in Sugar Hollow has found them before.  Chironomids of any size, are difficult to ID to the level of genus, let alone species (over 20,000 species world-wide), so this is as far as I go.  Still, a very cool find.

(Is that the midge head and proleg I see sticking out?)


3. Humpless case-maker Brachycentrus appalachia

This was not a surprise.  This is a caddis that is plentiful in this stream, especially at this time of year -- and I saw a lot of cases today.

But do you notice what's on the side of this case as well?  It was another midge case.

When I peeled this one off it measured about 2 mm.  This one, however, was not occupied.

4. Strong-case maker , Psilotreta labida

Not a good photo, but it was a very small larva.  It's the start of the season for these larva: more common in the next 2-3 months.

5. Saddle-case-maker, Glossosoma nigrior

And by the time I got around to photos of the Glossosomatids, they had all climbed out of their cases!

A fun day -- and oh yes, I did photograph one of the small minnow mayflies.  It was a male Plauditus dubius.  Tiny: 3-4 mm.

1 comment:

  1. Bob, I told you you couldn't stop.

    FYI, I am about halfway through the revision of Trichop larvae of NC. Hope to be finished in less than a month. Completely different format from the previous one and much more similar to the Mayflies of NC: Distro maps, seasonal graphs and up to date systematics, taxonomic characters and species lists. Also, at some point in the future (hopefully within the year) John Morse will be releasing a new book of EPT of the Southeast, with keys and diagrams. Should be pretty awesome,

    By the way, nice photos. I envy you your trips out west. Can't seem to swing it myself lately. Anyhoo, keep it up.