Monday, January 27, 2014

Nigronia fasciatus: the hellgrammite we find in small streams

I was about to call this one "Beauty and the Beast" -- no question about who's the "beast"!   But come photo time I couldn't locate the "beauty" -- a colorful, fully mature, Allocapnia small winter stonefly.

I had to get out there today before, once again, the temperatures take a dive, so off to my favorite small stream in Sugar Hollow in search of Rhyacophilids (freeliving caddisfly larvae).  I didn't find any, but it was still good to get out and turn over some rocks and sort through the leaf packs.

The hellgrammite we normally see is this ugly brute...

genus Corydalus.  But on occasion we run into the genus that lacks those frilly gills that we see on Corydalus.

The genus is Nigronia, and I've encountered two different species: N. serricornis (Lynch River -- see the postings of 11/21 and 11/22/12) and N. fasciatus.   They differ in the location and the length of the breathing tubes on segment 8.  These.

On N. serricornis, the tubes are short -- less than 1mm -- and fairly wide apart.  (For a full discussion of how to distinguish the two, see the Lynch River posting, 11/22/12.)  On N. fasciatus, the tubes are long, extending beyond the end of segment 9, and they're fairly close together.  The tubes on the large nymph that I found this morning measured about 1.5 mm: N. fasciatus.  Overall length was 33 mm.

One wierd looking critter!  Seems out of place in this pristine mountain stream.


I saw a lot of insects this morning, everything but the larva I was hoping to see.  The most common nymph that I found in the leaves was the large winter stonefly, Taenionema atlanticum.

And on the rocks: sides and tops, lots of Uenoids; bottoms, Epeorus pleuralis flatheaded mayflies -- they're plentiful at this time of year.

Oh, and by the way, I now feel quite certain that the Epeorus I found up at South River on 1/9 of this year -- this one

-- was Epeorus fragilis, not the more common Epeorus pleuralis.  Note the shapes of the heads and the shapes of the eyes.

I saw a lot of Uenoids this morning.  I hoped to run into N. mitchelli and/or N. aniqua -- which I find up at the top of this stream -- but alas, the four that I kept were all N. consimilis.
Unfortunately, I won't get up to the area where I know I will find mitchelli and aniqua until the weather warms up and we get rid of the snow.  N. consimilis: note the pale, reddish spots on the head.

They sure make beautiful cases in this little stream.

Below: young N. fasciatus found on 5/16/12.

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