Sunday, October 27, 2013

Make that Goera fuscula: my mistake

When I was at the point of posting yesterday's entry I had second thoughts and almost hit "delete" instead of "publish."  I should have.  After closer study this morning, I've determined that the Goerids I found yesterday were, species, Goera fuscula, not Goera calcarata.

The thing that bothered me yesterday -- that drove me to look at these insects again -- was the size. The larva that I examined was 11 mm: Beaty has "8-9 mm" for G. calcarata, but "9-11mm" for G. fuscula.  So let's have a look at Beaty's description of G. fuscula.

G. fuscula -- larvae 9-11 mm; 4 pairs of sclerites on metanotum; sternal thoracic plates distinct; face with central area smooth; posterior carina sharp and high.  Mountains only. Rare with less that 15 BAU records.  (Beaty, "The Trichoptera of North Carolina," p. 87)

1.  As I've already noted, the larva that I pulled from its case and measured was 11 mm; the case was 12 mm.

2. There are indeed 4 pairs of sclerites on the metanotum, not 3!  If you look directly down on the dorsum of the metanotum you'll only see three, but if you turn the larva on its side, you'll then see the 4th.  (Sclerites are bounded, dark spots on the fleshy body, normally containing setae.)

3. And yes, the sternal thoracic plates are distinct.  That's the first thing I noted this morning.  That on its own eliminates G. calcarata for the ID.

4. Head/face -- it's flat, almost depressed, surrounded by a quite clear carina.

Another look at the carina and head/face in a photo from my friend in Sugar Hollow.

Goera fuscula.  The tolerance value remains undetermined since it's an uncommon species.


One other point of interest on Goera in general.  On Friday, when my friend and I went to that small stream in Sugar Hollow, she saw some cases that looked like Goera.  They appeared to be sealed off for pupation, but she took them home for a look.  After a time, the larvae emerged -- the cases weren't sealed off at all!

The same thing happened to me yesterday.  Here's what I saw.

I was initially disappointed since I knew by the cases that these were Goerids: but then they emerged.

When I was reading Glenn Wiggins (Larvae of the North American Caddisfly Genera, 2nd edition, 1996) on the Goerids, I discovered that this is characteristic of the Goerids.  Look at this photo from my friend's collection, then I'll quote from his book.

"Larvae of the Goeridae are characterized by major modifications to the thoracic nota.  The pronotum is enlarged and thickened laterally; sclerotized plates of the mesonotum are subdivided into two or three pairs of smaller sclerites, and the mesepisternum is extended anterad as a prominent process.  These modifications are integrated to form a set of close-fitting sclerites forming an operculum that closes off the anterior opening of the case when the larva withdraws."(Wiggins, p. 226)

So, if you find one of these cases and it appears to be sealed -- don't be too sure!

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