Saturday, June 4, 2011

The $400.00 Trip to Buck Mt. Creek!

I lost my glasses.  I discovered this when I got home, a half hour later.  Having looked all over the house, I remembered taking them off while taking some photos.  So, this afternoon I turned around and went back to the stream.  Couldn't find them.  I hope you enjoy this "expensive" entry!

The gorgeous stonefly in the picture above is a Common Stonefly (Perlidae), genus Perlesta.  I've been finding immature nymphs at this stream for 3-4 weeks -- this one is close to mature.  The dark marks on the wing pads will turn just about black, while the tips themselves remain yellow.  Also, the yellow-orange color is very distinctive.

I found 10-12 of these in a single leaf pack, though at first I thought I had found some more Remenus Perlodid stoneflies.  As soon as I looked though my viewfinder I knew what I had.   I found nymphs at various stages of development: here's one that is quit a bit younger than the one pictured above.

As I've noted in previous entries, this genus has two features that we use for identification.  1) Subanal gills are present, and 2) there are "spinules" along the back of the head in a wavy, irregular row (Peckarsky, Freshwater Macroinvertebrates, p. 69).   Here's a closer look at those features from samples collected previously.

This is a genus that I've seen in only two places: Buck Mt. Creek and the Rivanna River at Darden Towe park.  And I've only seen them in May and June.

Now on to some of the "treasures" I found (but were they worth $400.00?!).  The first -- a Gomphid (Club-tailed Dragonfly), genus Hagenius.

Does anyone spot what's wrong with this picture?  The bug's upside down!  (Ugh!  It was just one of those days).  So, here's a picture with the dragonfly right side up -- but it's already preserved, no longer alive.

This is not the Gomphid we normally see (that's genus Ophiogomphus).  This is only the second Hagenius nymph that I've found, and they're big: this specimen was about 3/4" in diameter.  The defining features?   "Segment 4 of antennae vestigial or nearly so," and, ""Body very flat; abdomen nearly circular in dorsal view; paired tubercles on top of head" (from Peckarsky, Freshwater Macroinvertebrates, p. 48)   That the "body is flat and nearly circular" is clear from the pictures, so too is the fact that the primary wingpads are parallel, not divergent.  For the other features, we need a microscope view (click on the photo to enlarge it.)

This critter was wrapped up in the same leaf pack where I found all the Perlestas, so too was this Spiny Crawler mayfly, genus Eurylophella (my way to remember the Latin is to think of "you're-a-real-fella"!).

You may remember from previous entries that this genus differs from the one that we normally see, Ephemerella, in that the gills on segments 4-7 are "operculate".  Actually, the most obvious difference is that gills 4 and 5 are large, operculate, and cover the rest.  This is very clear in a microscope shot of the abdomen.

This is only the second time that I've seen this genus.  I did not see any Ephemerella Ephemerellids -- they seem to be gone.

One other surprise, something I see only rarely, a Whirligig Beetle (Gyrinidae).  This one is immature; mature larvae are darker yellow.

I don't want to tell you how long it took me to get these pictures!  This is an insect that hardly ever stops "whirling" around in the tray.  Here's another view.

I've seen these before in Buck Mt. Creek, always in June and July; I've also seen them in the Mechunk in Fluvanna County.  They're usually squirming around in the tangled grasses/vines/algae that cover some of the rocks in the summer -- but this one was inside a leaf pack.

What else did I see?  Flatheaded mayflies -- genera Leucrocuta, Epeorus, and Maccaffertium.  These are always on the bottoms of rocks.  The Epeorus nymphs that we see in the summer are probably Epeorus vitreus.  This species delights fly fishermen all summer long since it is a reliable evening hatch -- the "Light Cahill".  Epeorus pleuralis -- the Quill Gordons -- should be gone by now.  But this is Bob the fly fisherman talking, not a professional entomologist.  I also picked up a few small Brushlegged mayflies -- I'll see more of them here as the summer progresses -- and I had a couple of small minnow mayflies, but I couldn't find them at "picture" time.  I also had a small square-gill mayfly -- first of the summer, very exciting.  But I tried to balance a large rock on my knees and fell backwards into the stream spilling out all of my bugs -- so no picture.  (Did I mention that the day was a disaster?!)

Finally, I'm still finding the Perlodid stonefly, Isoperla holochlora.  This is a beautiful nymph: it's become one of my favorites.

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