Saturday, March 30, 2013

"Three Insect" Season at the Rapidan River

We'll get to the "three insects" that have taken over the river -- but this was clearly the find of the day.  This was a HUGE giant stonefly, Pteronarcys biloba.   How big was it?  The diameter of the petri dish that I use is 3 1/2".

So this nymph was 1 3/4" -- 2" long, not counting the tails!  That's roughly 45 -- 50 mm, and according to Beaty ("The Plecoptera of North Carolina," p. 28) that's as big as they get.  The prominent lateral abdominal hooks are clear in both of these photos, and here is a close-up of the "hook-like processes" on the anterolateral angles of the pronotum.

What a stunning insect!  I'd say that this one will be hatching real soon.

At the moment, if you sift through the leaf packs and turn over the rocks in this river, you'll see a lot of three different insects, all three of them of great interest to fly fishermen.   1) The bottoms of the rocks are still covered with the flatheaded mayflies, Epeorus pleuralis, though the hatch -- "Quill Gordon" -- has already begun.  According to a fly fisherman I ran into this morning, the Brook trout are feeding on them like crazy.  2) In the leaf packs, you'll primarily pick up Isoperla namata Perodid stoneflies and Ephemerella spiny crawlers, mostly E. dorothea.  The other things that I saw in significant numbers were free-living caddisfly larvae, R. fuscula (the green one), and midges -- very sizeable midges.  I. namata stoneflies will be hatching later this month as "Yellow Sallies," and E. dorotheas hatch later in June as the "Pale Evening Duns."  Time for me to get out the fly rods!


1. The Perlodid stonefly, Isoperla namata.  Around 11 mm.   These are difficult nymphs to photograph.  They're constantly on the move.

The wing pads are well spread on the nymphs in these photos, but remember, the wing pads turn black when they're ready to hatch.

2.  Spiny crawler mayfly, Ephemerella dorothea.  6-8 mm.  They come in various colors and patterns as we can see in these photos.

3. Spiny crawler mayfly, Ephemerella subvaria.  8.5 - 9.5 mm.  These will hatch -- some are probably already hatching -- as "Hendricksons."  This is a big mayfly, and this is a hatch that fly fishermen always enjoy (we can see our flies on the water!).    There are two flies we use for this hatch: the Light Hendrickson and the Dark Hendrickson.  It's a matter of gender: females are light in color -- both the adults and the nymphs -- and males are dark.   I found some of both.  Ladies first.

And then a male.

The females nymphs are bigger.

4. Finally some photos of a very large common stonefly, Acroneuria abnormis.   This looked to be about 1 1/4" -- 30 mm.

This one will be hatching in June or July -- the "Golden Stone."

1 comment:

  1. Just beautiful photographs. Such great information. As the old saying goes, a picture's worth a thousand words.