Wednesday, September 12, 2012

Back North to the South River: A Real Mix of Nymphs and Larvae -- but Some Beautiful Photos

Beautiful early fall weather at last: no steamed up lens on the camera, no sweating away in humid conditions.

I've not gone to the South River up in Greene county all summer: it's a small stream, and I assumed there would not be a whole lot of water.  To my surprise the water was still very low (we've had 6 inches of rain at our house in C'ville in the last month).  Still there were all sorts of insects on the rocks, even some in some leaf packs.  I can't say that any one insect "dominated" my findings, but that's not unusual for this time of year.  But the sunny conditions made for good photos.

Above, one of many Odontocerids (Strong case-maker caddisflies) that I saw in the stream, and I was pleased to get this photo with the larva almost crawling out of its case.  Look how clearly the "dorsal" hump that we see on most cased caddis larvae shows up in this photo.

Here are more photos of this beautiful caddis larva.

I'm still not totally sure of the species identification of the Odontocerids I find (the genus is Psilotreta).  But this last photo seems to indicate Psilotreta labida.    On P. labida, the anterolateral pronotal projections are long and acute.  That seems to be true on this larva.

The other find that pleased me today was a "new" netspinner species -- Hydropsyche betteni. [PLEASE SEE THE ENTRY POSTED ON 10/19.  THIS WAS LATER IDENTIFIED AS Ceratopsyche alhedra.]

As I was downloading my photos just a short time ago, I kept looking for a mark or a pattern of dots on the head -- I could not see a thing.  And sure enough, that's what tells us is H. betteni.  "Hydropsyche betteni larvae are typically black-headed with no light markings except those around the eyes." (Schuster and Etnier, "A Manual for the Identification of the Larvae of the Caddisfly Genera Hydropsyche...", p. 63)  Here is a close-up shot of the head.

I was a little surprised to find this common netspinner species in this very clean stream: H. betteni has a tolerance value of 7.9.  Still, it's well to remember that there is a mix of insects in all of our streams: tolerant insects have no trouble living in very good water, it's just that most intolerant insects have trouble living in water that's impaired.

Schuster and Etnier (p. 63) have some interesting things to say on this species.  "...this species is very common in small, warm-water streams.  It is often found in very large numbers, much like H. orris in large rivers.  H. betteni seems to be one of the most resistant Hydropsyche species to organic pollution.  Its ability to cope with and use the high concentrations of organic materials may contribute to the high numbers of individuals in the populations collected.  It has been found that, where H. betteni occurs, it is usually the most predominant caddisfly present.  It is often the only Hydropsyche species in the stream, but it is not uncommon for other species to occur with H. betteni.  The species most often collected with H. betteni is Symphitopsyche sparna [now Ceratopsyche sparna] which also seems to be resistant to high concentrations of suspended materials."

I've cited this passage at length for a couple of reasons.  1) I found these larvae in a small tributary to the South River, one which I'm sure does get very warm in the summer.  2) I picked up 3-4 in the short time that I was looking for things in the water.  And 3) I did find another netspinner larva, a small one, that I'm quite sure was Ceratopsyche sparna, even though the three light spots on the head we'd expect to see have not yet developed.

In one of my photos, I managed to get both species of larva together.


Just a few additional photos.

1.  A flatheaded mayfly, Leucrocuta hebe.

2. Flatheaded mayfly, Epeorus vitreus.  They're still around.

3. And our favorite summer small minnow mayfly, Acentrella nadineae.

1 comment:

  1. Etnier would probably tell you to look for two little bumps on the posterior margin of the frons on the head capsule. H. betteni has them, his description is "it looks like someone has been banging on the head with a ball peen hammer from the inside out". As weird as that sounds, it makes sense when you see it!