Thursday, July 28, 2011

Dragons and Damsels -- Back to the Rivanna at Crofton


If you want to see them, the Rivanna at Crofton is the place to go, and if you want to see them, go now.
This is a beautiful, pretty mature, Broad-winged Damselfly -- Calopterygidae.  It was big -- between an inch, and an inch and a half long.  Of the two damsels we see -- Broad-winged and Narrow-winged -- this one wins the beauty contest, with its slim, sleek body and very distinct antennae.  The tolerance values for genus Hetaerina broad-winged damsels varies with species: the NC DWQ tolerance lists has one at 4.9 and another at 7.5 (no determination is made for two additional species).   The common name for genus Hetaerina Calopterygids is "Rubyspots," and for photos of the adults, go to http://bugguide.net/node/view/362/bgimage.

Another photo before we move on.

While we do find broad-winged damselflies in our streams, without any question, our most common damselfly is the narrow-winged damsel -- Coenagrionidae, genus Argia.   While I found just this one broad-winged damsel today, I found six narrow-winged damsels.  Not as "delicate" as their competition, they're still beautiful insects.  The common name for genus Argia is "Dancer," and you can find photos of "Dancer" adults at:  http://bugguide.net/node/view/463/bgimage.  A couple of photos of a nice one that I found today.



But we mustn't ignore the dragonflies.  As I did the last time I was here, I found some "Emeralds" (family: Corduliidae).  In fact today, I found a lot of them.  There was one small one -- the rest were big -- about the size of a dime.  I'll show you the little one first.


And now one of the big ones, to which a lot of mayflies (flatheads, mostly) decided to cling!  I guess hitching a ride is better than swimming around on your own.


In the far left of the photo -- that tiny insect climbing the side of the petri dish is a three-tailed small minnow mayfly.  Tiny, tiny, tiny.  And I did find another Heterocloeon curiosm small minnow mayfly, the small minnow I found here on my last visit.  It too, was very small, so my photo isn't the best.


When I looked at this at home, I wasn't sure that it was a Heterocloeon, but I thought I should look to see if there were procoxal gills.  Oh yes! -- pretty obvious, right at the base of the front legs.  No doubt about it, small minnow mayfly, Heterocloeon curiosum.


And now for the unexpected treat of the day: a tiny "Little Stout Crawler" mayfly, family Tricorythidae (alternate name, Leptohyphidae), genus Tricorythodes.



If you want to see just how small this Trico (the fly fishing name) is, take another look at the photo at the top of this entry.  That's our Trico in the upper left part of picture!  This is a, typically, late summer mayfly, and we'll see them through September --  perhaps into early October.  I've found them in a number of streams (the Moormans comes to mind), but I've seen more at this site than anywhere else.
They do get a little bit bigger than this, but not a lot.  Ask any fly fisherman who has to tie on a size 20 or 22 imitation when the trout are keyed in on Tricos!

What's the key to recognition?  It's the large, grayish-brown operculate gills ("gill covers," actually) on the sides of the abdominal segments.  With magnification, they're easy to see, and you'll note that they're triangular in shape.  I liken them to the "chaps" worn by cowboys!


I might add that just about every Trico I've seen is similar to this in color -- i.e. they're normally yellow/orange.  Very unique.

One final shot.  There are a lot of clams and snails at this site.  So I took another photo of a Pleurocerid snail.  For those of you just starting out with identifying benthic macroinvertebrates, this clearly shows how "gilled" snails open on the right.


Oh.  Lots of netspinners, fingernets, flatheaded mayflies (Maccaffertium), and a few brushlegged mayflies.

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