Monday, October 6, 2014

Just checking: Yes, it was Goera calcarata

I assumed yesterday that the Goera (weighted-case maker) I found was species G. calcarata since that's the species I've found before at the Rapidan River.  But in this business, it's risky making assumptions about an ID -- so I thought I should check it, just to be sure.  Down to the microscope.

Steven Beaty, "The Trichoptera of North Carolina," p. 87:  G. calcarata -- larvae 8-9 mm; 3 pairs of sclerites on metanotum; pronotum with central raised area and anterior margin with conspicuous spicules; sternal thoracic plates indistinct.  Common in the Mountains and Sandhills.

1.  This larva was almost exactly 8 mm.

2. The 3 pairs of sclerites on the metanotum and the central raised area on the pronotum both came out very well in one of my microscope photos.

3. On. G. fuscula larvae, the "sternal thoracic plates" -- you will recall -- are distinct and look like this.

Here's a look at our larva -- no plates to be seen.

It was indeed Goera calcarata.

I suspect that Goeras are "stream specific" in terms of the species, and G. fuscula larvae are apparently fairly uncommon (Beaty on G. fuscula "Rare with less than 15 BAU records.")  (BAU = Biological Assessment Unit)  In Entry Run, I see nothing but G. fuscula; in the Rapidan River, G. calcarata.  But don't you wonder what determines which species is where?   The Rapidan and Entry Run are both in the mountains, both flowing out of the Blue Ridge.  Maybe it's size: Entry Run is a small, first order stream; the Rapidan is not.

But think this one over.  My good friend who lives in Sugar Hollow on the banks of a "pristine" first order stream, finds nothing by G. fuscula: but on the other side of the valley -- less than 1/4 mile away -- in another "pristine" first order stream, I've found nothing but G. calcarata.


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