Friday, November 23, 2012

Good News and Bad News from Buck Mt. Creek

The good news is that I found quite a few Uenoid case-makers (caddisfly larvae) in Buck Mt. Creek this morning: the bad news is that someone is messing around with the stream.

Bad news first.  Buck Mt. Creek has changed dramatically since I was last there less than three weeks ago.  While the water is clear,  the bottom is, all of a sudden, silted up.  Rocks are covered with silt, the submerged leaves in the stream are covered with silt, and the grass-like vegetation that covers the bottom in places -- the long kind that sways back and forth with the current -- looks like it has "clouds" of silt on everyblade.  Result:  I didn't see a whole lot of insects, and most that I found -- whether in leaf packs or on the bottoms of rocks -- were covered with sand.  The brush-legged mayfly nymphs that I saw had turned pale in color: I'm not sure what that means -- but it can't be good.  If there are readers in the Charlottesville area who know what's going on, I'd sure like to find out about it.  It was very, very discouraging.  This is/was an excellent streams for insects.

Now, back to our Uenoids.  This is a caddisfly larva that makes its case out of grains of sand and small pebbles, and we see a lot of them in local streams during the winter.  You'll see their cases, normally, on the tops of the rocks -- they'll look like light-colored dots.  When its case is put upside down, the larva look like this.

The Uenoid genus we see in our streams is Neophylax, one of five genera noted by Wiggins in the caddis family Uenoidae (Glenn B. Wiggins, Larvae of the North American Caddisfly Genera (Trichoptera), 2nd edition [University of Toronto Press, 1996]).   But "Uenoidae" is a relatively new caddisfly family, and in 1977, in the 1st edition of Larvae of the North American Caddisfly Genera, Neophylax was listed as a Limnephilid (Northern case-maker) genus.

Uenoid cases are commonly tapered like the one in the photos above, and they often have 3-4 larger pebbles on each of their sides as we can see in this photo.

The cases that I found this morning were still very small, measuring 5-6 mm: the larvae inside were smaller still, about 3.5 mm.  And here's what the larva will look like when it slips out of its case.

Like most Limnephilids, the Unenoid has lateral humps on the first abdominal segment; there's a dorsal hump as well which we could see by turning this over.  But the key feature we need to see for certain ID is a "T" shaped sclerite on the underside of the head.   For a photo of this, see the entry posted on 12/21/10.

We'll be seeing Uenoids all the way through the winter, and I hope to be able to nail down the "species" ID sometime soon.  Beaty describes 10 Neophylax species that are found in North Carolina ("The Trichoptera of North Carolina," p. 86).


My other findings this morning?  A few small winter stoneflies, genus Allocapnia, but not a lot, and some Helopicus Perlodid stoneflies.

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