Friday, October 19, 2012

Making the Case for yet Another Common Netspinner: Ceratopsyche alhedra

On 9/12, I posted this photo of what at the time I thought was the netspinner, Hydropsyche betteni.  I'm now pretty sure I was wrong; it was Ceratopsyche alhedra.  C. alhedra is a very intolerant netspinner with a TV of 0.0; H. betteni is a very tolerant netspinner with its TV of 7.9.  This larva was found in very clean water in the South River coming out of the Blue Ridge.  I'm pleased to know that my initial assessment was wrong, and I'm certainly not surprised by the ID.

Having found what I am certain was an H. betteni larva in Mechunk Creek on Tuesday, I decided to compare the two larvae closely today with microscope views.  That's when I discovered a major mistake.  The netspinner found on 9/12 at the South does not have "scale" hairs on the abdominal segments.  Here is a microscope view of the abdomen of a Hydropsyche larva: the "scale" hairs are the short, wide, pointed, very black hairs.

Now look at the abdomen of the larva I found on 9/12:

I just don't see any scale hairs.

Back to the books.  Which Ceratopsyche species has a head that's totally black, that would look like H. betteni?  Steven Beaty, "The Trichoptera of North Carolina," p. 72:

C. alhedra -- larvae large; head uniformly black with posterior margin of head pale.  Prefers clean streams and fast current.  Mountains.  Uncommon.  Very intolerant.

I think that's a match.  But let's look at a source with greater detail -- the EPA Manual on Hydropsyche and Symphitopsyche (now Ceratopsyche) genera by Schuster and Etnier.  The relevant pages are 45-47.  I'll not cite their complete description; I'll just focus on features that I can show you.

Symphitopsyche [Ceratopsyche] alhedra

Description: Head coal black except for circular areas around the eyes and large subrectangular yellow area on posterior lateral aspects of genae. ... Labrum coal black with short, black setae margined by tuft of long, yellow setae.  Mandibles dark brown to black."

In the photo below we can see all three of these features: the "subrectangular yellow area" at the back sides of the head; the black labrum, or at least the top of the labrum covered with setae; and the dark brown/black mandibles.

I think that's a pretty good fit.

My apologies for not being more careful with this ID in the first place.  But, when I make a mistake, I always try to correct it.  And it's always a joy to realize that another species has been found in our streams.

More photos:

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