Tuesday, September 17, 2013

Odontocerids (Strong case-makers) at the Rapidan River

With very little to see in our local streams at the moment, I decided to return to the Rapidan River where I knew I could find lots of insects.  One of my goals was to find some Odontocerids -- Strong case-maker caddisflies -- for photos, and it wasn't much of a problem.  When I walked into the stream, I looked down at some submerged rocks in the slow water -- and there they were.  They graze on the algae and periphyton on the tops of the rocks, so you don't have to lift a thing to see them.

Strong case-makers -- at least the genus we commonly see, Psilotreta -- hatch as "Dark blue sedges" in late spring/early summer, but the time to see them in their beautiful cases is now.    Ames (Caddisflies, p. 211) says that he sees them in New England in the fall, from August through October.  Some make tubular cases; others have cases that are long, tapered and curved.  I found both types of cases this morning, but I forgot to photograph the plain, tubular case.

Look for them in clean mountain streams.  I see them every year in the Rapidan, the North Fork of the Moormans, and South River up in Green county.  The most common species we see is Psilotreta labida.

Other photos:

1. Small minnow mayflies, Acentrella nadineae.  I also saw Baetis intercalaris nymphs, but somehow I managed to break their tails.

and this one decided to perch on this humpless case-maker case

2. And yes, as I expected, I again saw a lot of humpless casemakers -- Brachycentrus appalachia.

If you look closely at the head of this larva, you can make out the 5 black stripes that help us to key out the species to B. appalachia.

3.  I saw quite a few fingernet caddis larvae this morning, genus Dolophilodes.  Note the assymetrical notch on the leading edge of the head.

4. And you guessed it, that's a small roach-like stonefly alongside our larva.  There were lots of them in the leaf packs.  They're tiny at this time of year.

5. One of those young common stoneflies I've been talking about.  This one is Paragnetina immarginata.

6. And I found both Giant stoneflies that inhabit this river: Pteronarcys proteus and Pteronarcys biloba.  The lateral projections on the abdominal segments differ dramatically on the two as we can see in these photos.

P. proteus

P. biloba

P. biloba cerci (tails) are quite a bit longer than those of P. proteus.

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