Wednesday, November 21, 2012

One strange looking Hellgrammite: Nigronia fasciatus

(Note: This hellgrammite is mistakenly identified in this entry.  It should be Nigronia serricornis.  See the following entry.)
Of course I should be talking about small and large winter stoneflies and all those Perlodid stoneflies that are showing up now -- but we'll be seeing them in a regular way in the weeks ahead, and this is an insect that we see only rarely.  It's a hellgrammite -- a "fishfly" if you prefer -- family Corydalidae, species, Nigronia fasciatus.  This is not the hellgrammite that all of us are used to seeing on the rocks in the streams.  That would be this one...

This is genus Corydalus, and it's got some pretty mean jaws (some of us have found out the hard way!).  The genera are similar in a couple of ways: both have two pairs of hooks at the end of the anal prolegs, and both have "filaments" sticking out from the abdominal segments.  But Corydalus has something you don't see on Nigronia nymphs -- clustered gills between those filaments.

Nothing like that on our Nigronia nymph.

I've already posted an entry on this type of fishfly (5/17 of this year), so I'd refer you back to that entry for the details on how we arrive at the genus ID.  Essentially it has to do with finding a pair of "respiratory" tubes at the end of segment 8 (dorsal side).  These:

Or these:

And note the size: 1 1/2 times as long as wide.  Nigronia.  The species ID, fasciatus, is determined -- as I recall (I can't locate my source at the moment) -- by the amount of separation between those tubes.  And one more photo, since the two pairs of hooks at the end of the prolegs are not clear in my live photos, here's a closeup microscope view.

Nigronia fasciatus.  This one is from the Lynch River.  Size: 25 mm.  Tolerance value: 6.1.


So much for the "beast," let's have a look at a "beauty."

The Perlodid stonefly, Clioperla clio.  The Lynch was loaded with them.   Note how the posterior edges of the wing pads are really starting to bow, and of course, the colors and patterns are starting to richen as we watch them start to mature.

In addition to the C. clios, I did find a number of small winter stoneflies today -- one was eaten by this big Clioperla! -- and I found a number of tiny Perlodid stones that I was anxious to photograph and ID.  Unfortunately, on my way back to the car I stumbled and fell, and there went most of my insects!  I did find one still swimming around in my bowl.

A very, very small (2.5 mm) Diploperla duplicata.  I found a fully mature D. duplicata in this very same stream on May 14th of last year (2011).  Quite a transformation.


Below: a Clioperla clio traffic jam in my petri dish when I was getting my photos.

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