Thursday, February 23, 2012

The Leuctrids (Rolledwinged Stoneflies) Start to Show up in Our Streams

They're small, and I've only seen them in very small (narrow) streams, mostly very clean streams that flow through the mountains.  The tolerance value is only 1.5 for the genus "Leuctra," which is the only one that I've seen in this region.

Monitors sometimes confuse Leuctrids with small winter stoneflies.   But if they look closely they should be able to tell them apart, and, they don't overlap that much in our streams: by now, most small winter stoneflies are gone, and the Leuctrids are just coming on (they normally hatch in August -- November).  In any event, Leuctrids have a long, thin abdomen -- small winter abdomens usually have a slight bulge in the middle -- and the rear wing pads on Leuctrids are always longer than they are wide (see the photo below), not the case with most small winter stoneflies.

The genus Leuctra is descibed by Beaty ("The Plecoptera of North Carolina," p.2) in the following way:
"Nymphs 6-9 mm; labial palpi extend past rest of labium; hind wing pad longer than its greatest width; first four abdominal sternites with pleural folds; abdomen parallel sided; pair of terminal setae on lobe of last abdominal segment."

That the labial palpi extend beyond the glossae and paraglossae is easy to see.

And, I think you can distinguish the pleural fold in this photo.  The fold occurs right where there's a color change at the edge of the segments 1-4.

As for the pair of terminal setae -- well, tough to see on our nymph since they were covered with silt.

I should find some better Leuctrid examples as we advance through the spring.  Another look at our nymph.

And, here's a microscope photo of a mature nymph, taken two years ago.  When they mature, their wing pads and abdomen often contrast in color.


I was back in Sugar Hollow this morning since a lot of our streams are, once again, a little bit high following the melting of 6 inches of snow and a quick shot of rain.  But, I always find beautiful insects when I go to these streams.

1. Flatheaded mayfly, Epeorus pleuralis.  You can pick up just about any rock, and you'll see them scamper for cover.  The stream is loaded with them.  This is the mayfly of the moment.  Oh, but I also saw a lot of Leucrocutas which, at the moment, are just too small to pick up for pictures.

2. And the "stonefly" of the moment -- what else? -- Isoperla nr. namata.  The rocks are covered with flatheads; and the leaf packs are loaded with the Perlodid stonefly I. nr. namata.  Sure with quite a hatch of "Yellow Sallies" from late March through April.

3.  But I also found more of the big Perlodid, Malirekus hastatus.  You really have to be careful with these -- they'll eat anything they can get hold of.  I lost a number of flatheaded mayflies to their hungry jaws and an I. nr. namata as well.  But, they are beautiful insects.

4. I saw quite a few Uenoid case-maker caddisfly larvae: some were crawling around on the top of the rocks (rocks that were underwater, that is), others have already sealed up their cases and entered pupation.  Beautiful Uenoid cases in this particular stream.

5. And in this photo, a free-living caddisfly larva (R. fuscula) decided to perch on one of the cases in which a Uenoid has gone into pupation!  (Notice how the Uenoid has sealed its case at one end with an orange pebble.)

6. Another free-living caddisfly larva, Rhyacophila nigrita, a species that's common, it seems, in this stream.

7. And finally, a Chloroperlid (Green stonefly, genus Sweltsa) that has started to move toward maturity, getting darker in color and with wing pads that are "rounding" into shape.

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