Wednesday, December 14, 2016

A review of the large winter stone flies (Taeniopterygidae)

Went out to Buck Mt. Creek this morning where I found the first Uenoidae (little northern case-makers) of the season, about which I'll post something tomorrow.  But I also found some large winter stoneflies -- pictured above -- the species we see in a lot of our streams, Taeniopteryx burksi (or possibly maura).   And this is when we see them, from November through January, with a few around in February as well.  With a TV of 6.6, it's a tolerant insect, but it's still a beauty.

With the brown body and the pale medial stripe that runs from the head to the tails, it's easy to spot, and if there's any doubt in your mind about what you've found, flip the nymph onto its back.  There'll you'll see these.

Long telescopic coxal gills at the base of each of the legs -- to me they look like bean sprouts.

While T. burksi is the most common large winter we find in our streams, it's not the only one you're likely to see if you're out there monitoring streams.  And in the very same streams where T. burksi/maura hangs you'll probably run into this one,

which is Strophopteryx fasciata.  Different colors with a mottled appearance on the head, pronotum and wing pads, and banding on the terga.  No coxal gills -- so don't rely on that feature to identify all large winter stoneflies.    One of the keys to the S. fasciata ID is the abdominal banding.  On each tergite there is a dark anterior band and a medial row of dark dots.

Also important is the ventro-apical plate which when looked at head on looks like this.

That last point is important since it's an important way to distinguish Strophopteryx nymphs from the third species of large winter stonefly we find in our streams -- Taenionema atlanticum.

Apparently there are Strophopteryx nymphs that like T. atlanticum, are uniformly brown in color (though I've never seen them).  That's why it's important to look at the ventro-apical plate.   And while the Strophopteryx plate has concave shaped sides, those of Taenionema curve straight down to a point.

But I don't think you'll find T. atlanticum nymphs where you find our other two species.  T. atlanticum only occurs in high quality, cold water streams -- like the headwater streams in Sugar Hollow that I go to -- where I've never seen T. burksi/maura or S. fasciata.

A look at some Uneoids tomorrow.

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