Saturday, October 22, 2011

Photos: More Surprises at the Rapidan River

You may wonder why I spend so much time at the Rapidan River in Madison County, but it's really quite simple.  1) The insects here are prolific: I never have to hunt around looking for the odd mayfly or stonefly; 2) I find insects here that I find nowhere else -- quality insects; and 3) the location is right at the base of the Blue Ridge, and it's a beautiful drive -- the last 10-15 miles anyway.

On September 13th (you can look back at the entry) I was surprised by some of the insects I found in this river; the same was true today.  And we may as well begin with the photo at the top of the page.  On the left is a pronggilled mayfly (genus Paraleptophlebia); on the right a small minnow mayfly, Baetis pluto.  I haven't seen Baetis pluto since June 19th at Buck Mt. Creek (you might want to look back at that entry).

I did not expect to see prong-gilled mayflies this early, and they were all over the place -- very small, crawling around in the leaf packs.   This is a mayfly that we see in very few streams, but the Rapidan is a good place to look.  It has very unusual gills -- they look like "tuning forks".  Here are some photos: the "forked/pronged" gills are very clear.

On the small minnow mayfly -- at the stream, I was quite sure it was Baetis intercalaris; I found some here on my last trip.  I didn't realize that it was, in fact, Baetis pluto until I downloaded the pictures.  The
pattern on the head gives it away (it appears to be longitudinally striped -- alternating light and dark bands), and very obvious from the photos is the abdominal pattern: tergum 5 is pale in color, 6 and 7 are dark.  Have a look (and look back to the nymph that I found on 6/19).

And a side view,

So, I found some nymphs of this species that were nearly mature in June, and now here's one that is nearly mature in October.   Does that mean that this species has two hatches a year?  I can't tell for sure since my samples were found in two different streams.

More nice surprises today.  On September 13th, you may recall, I found a small Perlodid stonefly, genus Isogenoides, the first Isogenoides I've seen in Virginia.  Found another one today, and it's noticeably bigger than the one I found in September.  The species is Isogenoides hansoni.  Keys to species ID include, 1) the dark banding on the anterior and posterior edges of the abdominal segments, 2) the pale "M" shape on the head, and 3) the pale yellow dot between the lateral ocelli.

And at home with the microscope, I got some excellent photos of the morphological features used for genus identification -- 1) presence of submental gills, and 2) on the mesosternum, the median ridge extends to the transverse ridge.

I expect to see really tiny Perlodids in the other streams I explore by the end of this month or in early November.  But they'll be different genera: Clioperla or Diploperla are normally the first two that we see.

I also found, on 9/13, a really small spiny crawler, the beautiful nymph that will mature here sometime in late winter -- Ephemerella subvaria.  I found two more today, and they too were quite a bit bigger than those that I found here last month (look back at the post of 9/13).   A couple of photos of this colorful insect.

They're simply amazing.

Just three more things.

1) A Giant stonefly -- this one was well over an inch long.  They really are "formidable" looking critters.

2) A fair-sized free-living caddisfly larva.  (So, they're back.)

3) And, an Odontocerid (Strong case-maker caddis), genus Psilotreta.  I knew they were in here: it was just a matter of time before they showed up.

So another delightful day at the Rapidan River.  I'll be heading back there next month -- who wouldn't go?!

Below: The Rapidan River in autumn at the entrance to the Shenandoah National Park.

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