"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!

Photos:

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."

Mature! Heterocloeon amplum and Helopicus subvarians -- Doyles River

The water in the Doyles River has finally dropped and cleared enough to allow me to resume looking for insects.  This morning, I was hoping to find two different things: the small minnow mayfly, Heterocloeon amplum, and the Perlodid stonefly, Helopicus subvarians.  Both, by this time of the year (end of March/early April) should be mature.  And they are.

In the photo at the top of the page, a beautiful, male, H. amplum small minnow mayfly.  The color is odd -- totally black -- but I've seen it before at the Doyles and up at Lynch River.  It was also large, about 8.5 mm.  The mature H. amplum that I normally see -- in terms of the color -- is this one.

Again a male, this one was about 7.5 mm.  Here are additional photos of both.

They're beautiful insects when they're mature, and the "Blue-winged Olive" hatch should begin anytime now.
________________

And here's the Perlodid stonefly, Helopicus subvarians.

You'll notice that this nymph was chewing away on a black fly larva: they must be pretty tasty (though I have no intention of checking that out!).

H. subvarians is the largest Perlodid stonefly I see in the course of the year (this one measured 20 mm), and for that matter, H. amplum is the largest small minnow mayfly I see in the course of the year.

I thought I might review how we ID this particular stonefly using Steven Beaty's "The Plecoptera of North Carolina," p. 21.

Genus diagnosis: Lacinia triangular, bidentate sometimes with a small tuft of setae originating on a small knob and with a row of marginal hairs approaching base.

Definitely.  He continues, "right mandible with five teeth; prominent submental gills, about three times longer than wide."  I didn't examine the mandibles, but the submental gills are easy to see.

"Frons with a complete dark transverse band through ocellar triangle; cerci with a dorsal fringe of setae."  I'm afraid that the dorsal fringe on the cerci does not show up very well in my photos: the dark transverse band on the head/face, on the other hand, is obvious.

On the species ID (H. subvarians), Beaty says the following:

H. subvarians -- nymphs 17-20 mm; anterior margin of dark, transverse ocellar band a straight line or mostly so; occipital spinules grouped into broad patch of 2-3 irregular rows.  Nymphs occur September through April in the Mountains and Slate Belt.  Relatively uncommon.

The transverse band is indeed "mostly" straight, and there are indeed 2-3 irregular rows of occipital spinules.

________________

I hope to get up to the Rapidan River on Saturday where all sorts of things should be maturing.

Predators! Feeding Perlodids and Chloroperlids in Sugar Hollow

Back to Sugar Hollow this morning to explore a jewel of a stream that pours down the mountain near the home of my friend.  The water there is crystal clear.

We didn't find a lot of insects in the leaves and the rocks, but I was pleased to see some fairly mature Chloroperlids (green stoneflies) -- pictured above.  Note how the inner edges of the wing pads diverge, and note the dark hair that covers the wing pads and abdominal segments: both are indications of genus Sweltsa.

I also picked up a nice Ameletid mayfly (Ameletus lineatus, I think -- never got a chance to check it for sure) and a Perlodid stonefly, Isoperla similis.  This little beauty.

But I wasn't vigilant when it came to keeping an eye on the bugs in my tray.  As a result, I never got a chance to photograph that nice Ameletid: before I got to it my "nice" Perlodid got ahold of its throat!

And I noticed a black fly larva as I was taking my photos -- but my Chloroperlid noticed it too!

Little did he know that he'd be sharing that larva with the I. similis nymph.  Between them, they disemboweled it.  Ugh!

________________

If you read this blog in a regular way, you know that this is not the first time that this has happened.  In the winter of 2011, I lost a small minnow mayfly (H. amplum) to a voracious C. clio Perlodid:

Then last fall, a Perlid (common stonefly) bit into a common netspinner while I wasn't watching.

________________

Perlids (common stoneflies), Perlodids (Springflies/Stripetails), and Chloroperlids (green stoneflies) are predaceous -- they like to eat meat.  And they're not very choosy when it comes to picking their prey.  I've noticed a preference for small minnow mayflies (!), but as we can see, black fly and caddisfly larvae will do perfectly well!  And, they will go after each other.  The Chloroperlid in the photo above was chased a couple of times by that I. similis nymph before they both took that black fly to lunch.

The "mouths" of Perlids, Chloroperlids and Perlodids have rather powerful-looking glossae(g) and paraglossae(p) which I suspect are designed for tearing things apart.  Have a look.

Perlid labium:

Perlodid labium:

Chloroperlid labium:

Compare those with the p and g of a large winter stonefly, a stonefly that lives on a diet of algae and leaves (they're shredders, collectors and grazers).

In any event, lesson learned once again -- always carry two trays for collecting your insects!
________________

Note:  The I. similis Perlodid remains one of my favorite stones in terms of its colors and patterns.  We should see mature nymphs this month and next.  My best photos of this particular species date from 4/13/11.  The two nymphs below were in the same stream we went to today.

________________

Rhyacophila carolina at a small stream in Sugar Hollow

The plan was to go to Buck Mt. Creek where I'm sure the winter insects -- H. amplum small minnow mayflies, Clioperla clio Perlodids, etc. -- are fairly mature.   But BMC is still high, fast, and off-color.  I'm still restricted to the small, first order streams in Sugar Hollow: I'm not even sure that the Rapidan is doable yet.

My choice today was a small stream that spills into the Moormans not far from the first bridge.  This is only the second time that I've stopped there.  I sure didn't have to look very hard to find lots of interesting insects.  While here, too, the E. dorothea spiny crawlers dominated my findings, I was most excited about this free-living caddisfly larva, Rhyacophila carolina, one that I've only seen in a few of our streams.  Tolerance value: 0.4.

There are three features that distinguish this species, one is the color of the head and pronotum: golden brown (Beaty, "The Trichoptera of North Carolina," 60).   That's very clear in all of my pictures.

Number two -- there are no ventral teeth (denticles) on the anal claws.

And number three -- the sides of the head are "rounded," not "parallel."  Compare R. carolina with R. nigrita.

R. carolina, according to Beaty, is the "second most common Rhyacophila in NC."
________________

For the rest, pretty much what we'd expect to find in a small mountain stream at this time of year.

1. Spiny crawler mayflies, E. dorothea.  As I did at the Whippoorwill last week, I found both the large nymphs that are dark brown with a pale dorsal stripe,  nymphs that are already fairly mature,

and some much smaller nymphs that still have a long way to go.  However, these E. dorotheas were not so much "speckled" -- as those at the Whippoorwill were -- as highly patterned, and one was a very odd color, very orange.

2. A Limnephilid (Northern case-maker), genus Pycnopsyche -- the one with the three-sided case made out of segments of leaves.

3. Common stonefly, Eccoptura xanthenses.  I saw quite a few -- this was their kind of stream.

4. And as you can see in that photo, I found some Uenoids, including two very small Neophylax aniqua.  Here is a close-up of the one in the photo above.  The blunt tubercle on the head is visible even though the larva was only 2.5 mm.

Here's a second N. aniqua: this one was 3 mm long.

I also found two N. concinnus Uenoids: the photos of this one were the best.

N. concinnus larvae have a small, rounded tubercle on the head which you can see if you enlarge this photo.   They also have a "spiculate" pattern on the frontoclypeus and fairly large spines on the anterior of the pronotum.

And no clavate gills.

_____________

Note the difference in size of two of the E. dorotheas.