Friday, June 14, 2013

Our summer "annuals" -- Neoperlas and Perlestas (common stoneflies) -- at the Doyles River this morning

I wasn't sure I'd find anything at the Doyles River this morning.  After 7 inches of rain in the last 7 days, I wasn't sure I could even get into the stream.  Well, the water was high and fast, but it was fairly clear.

Most common stoneflies (Perlids) are multivoltine, meaning they mature over 2-3 years.  But there are two "univoltines" (i.e., the life cycle is only one year in duration), and we see both of them mainly in June: Neoperlas and Perlestas.   I've seen very few Neoperlas: before today -- I've only seen them in Powells Creek in Crozet.  Perlestas, on the other hand, are all over the place at this time of year.  This agrees with comments by Beaty ("The Plecoptera of North Carolina," pp. 17 and 19): Neoperlas are "uncommon in the mountains," while Perlestas  are "common and widespread."   Both, by the way, are fairly tolerant: tolerance values are Neoperla, 2.1; Perlesta, 2.9.

Neoperla Perlids are fairly easy to spot and can be identified with a loupe: they have large, lateral ocelli at the back of the head but lack the anteromedial ocellus that we find in the other Perlid genera.  They also have a transverse occipital ridge.

Most Neoperlas have not been described to the level of species (Beaty, p. 17), so our ID remains at the level of genus.   But nymphs of two of our species have been described -- N. clymene and N. carlsoni --so I hope to look further into the issue of the species ID of the nymphs that I find in our streams.

I found Perlesta nymphs of various sizes this morning, but this one was clearly mature.  Perlestas, like Neoperlas, have not yet been ID'd to the level of species, though according to Beaty (p.19) a lot of work is being done on this issue right now.  Like almost all of the Perlestas I see in our streams, this one is very speckled (the abdomen), but there is one thing on this nymph that strikes me as being unique and may be species specific: that's the dark brown/black ocellar triangle.

By way of contrast, take a look at this Perlesta that I found at Powells Creek on June 16th of last year.

And look at the head:

The dark brown ocellar triangle is not distinct from its anterolateral projections.  Quite different.  Something to look for as we move on through June since this is the most common stonefly we are going to see.

Below -- a "friend" who watched me closely as I was taking my photos.  Can anyone tell me what this might be?  Pretty neat looking bug.