Tuesday, July 8, 2014

What are Lepidostomatid case-makers doing in the Rivanna River in summer?

The water in the Rivanna is dropping and clearing -- and really warming up.  So I went to the Rivanna at Crofton to see if I could lift any rocks.  I could -- but I had to stick close to shore.  Still, I saw a lot of insects, though most things are small.

And I found, as you can see, a Lepidostomatid case-maker.  I've seen them before in this river, but it's something I don't understand.  The genus is the same that we see in the winter in spring -- Lepidostoma -- a larva which makes a four-sided case "constructed of quadrate pieces of plant material" (Beaty, "The Trichoptera of North Carolina," p. 81).  Tolerance value: 1.0.  We see a lot of these in the winter and spring, but they're always in small, very clean, cold mountain streams, often head water streams.  So what are they doing in this big, warm, not so clean river in summer?  I assume this is a matter of species, which, unfortunately have not yet been described.  Beaty names 22 species in North Carolina.   Whatever the answer, they're here, though not in very large numbers.

I have to admit that the cases made by those that I find in the winter are aesthetically much more pleasing.  And remember that some begin their cases with grains of sand.

Here's a pair that I found in Sugar Hollow on 3/3/12.

And another from 1/30/12.

I'll have to see what the entomologists say about this one.

Other photos:

1. The "Rivanna River" Acroneuria abnormis Perlid.  No "M" visible on the head, and no banding on the terga.  (Have a look at the entry of 10/4/13.)  Still very small.

2. A VERY freckled genus Perlesta Perlid.  Note the setal row on the occiput and the presence of anal gills (= Perlesta).  (Red eyes = male?)

3. And among the many flatheaded mayflies I saw, I found our first Heptagenia of the season: Heptagenis marginalis.

Heptagenia flatheads, as opposed to Leurcrocuta flatheads, have "fibrilliform" on gill 7.

We'll get better photos of this one later on in the summer.  This one was taken on 8/8/12.

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