Friday, May 31, 2013

Drunella spiny crawlers again -- but the common stonefly Perlesta is taking over the stream: Up to the Moormans

One of the better photos I've gotten of the spiny crawler Drunella tuberculata.  What a beauty!

I decided to look at the Moormans this morning.  I have a site that I visit right below the first bridge in Sugar Hollow.  I expected to see flatheaded mayflies, small minnow mayflies, and the common netspinner caddis.  I did.  But once again I saw a lot of Drunellas, D. tuberculata and D. cornutella -- two days in a row!  They were mostly in clumps of leafs and twigs, though I did find one cornutella just strolling along on a rock.  I photographed two D. cornutellas which turned out to be a male and a female.  Spiny crawler male nymphs have big red eyes just like we see with male small minnow mayflies.



I guess D. cornutella is more common than I had assumed.

But the big story today -- Perlesta Perlids (common stoneflies).   I had forgotten how they "blossom" in a lot of our streams when we get into June.

I picked up 20-30 in a short time this morning -- most were in leaf packs.  I saw one A. abnormis Perlid and one I. holochlora Perlodid: everything else (stoneflies) was Perlesta.  Three features to look for: 1) anal gills are present; 2) the abdomen, actually most of the body, often looks speckled; and 3) the setal row on the occiput is sinuate with gaps.  (See Steven Beaty, "The Plecoptera of North Carolina," p. 19)

I had also forgotten that Perlestas are voracious predators.  I found a nice, fully mature Plauditus dubius small minnow mayfly this morning that I was sure would make a nice photo: one that looked a lot like this.

I eventually found it in my tray -- well, what was left of it -- in the mouth of that innocent looking Perlesta in the photo above!  Perlestas, by the way, are "univoltine" having a one year life cycle.  That's why we only see them at this time of year and watch them mature in 2-3 months.  Very pretty when they mature.


One other insect that I don't see all that often, but one which is fairly common at this site in the Moormans -- a Polycentropodidae, "Trumpet-net maker" caddisfly larva.

The muscle scars on the head are very distinctive.  This one, like all of the Polys I've found, was Polycentropus in terms of the genus.   It's the "X" on the anal proleg that gives that away.


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