Saturday, July 30, 2011

A Quick Look at Buck Mt. Creek on a Hot Summer's Day

Yes, yes, I know -- we all want to see those beautiful mayflies and stoneflies and caddisflies, but they do share the streams with some rather scary characters.  Megaloperta, Corydalidae (Corydalus cornutus, I'm told) -- a Hellgrammite, or Fish Fly, or Dobson Fly to most of us who've been seeing them since we were kids.  This is 2 1/2" - 3" long -- a big one -- so if you want to grab it, I'd advise you to stay away from those "pincers" on the front of the head.  A closer look:

If you're this close, you're too close!  They will grab your fingers -- and it hurts!   But they're not all this big at this time of year.  In fact, right now, you can find infants and toddlers and teens -- as well as these monsters that are preparing to hatch.  (Have a look at recent entries from the Mechunk Creek and the Rivanna River at Milton.)  Some others that I've found this summer -- a baby and then something like a teen.

I took a couple of photos of this big boy today -- well, could be a girl I guess (?) -- where we can notice some interesting things.  First...

You can get an idea of the size of this baby by noting the other nymphs in the photo: two flatheaded mayflies, a brushlegged mayfly, and a young hellgrammite that looks like it's climbing aboard!  You can also see (I encourage you to click on the photo to enlarge it) the two claws on each anal proleg that help us ID this critter, no matter how small it might be.  And finally, you can make out the "frilly gills" that can be found between each of the filaments on abdominal segments 1-8 and 10.  We often miss seeing those "gills," because they won't be in use unless the hellgrammite is in water that's deep enough for it to draw the oxygen out of the water.   Here's a photo that helps us to see them a little bit better.

Of course, this is not the only thing that I saw today.  I saw a lot -- and I do mean a lot -- of brushlegged mayflies.  Most were in leaf packs which are already starting to form in the stream.  There were also a lot of flatheaded mayflies -- mostly genus Maccaffertium.  But I did find a few Heptagenias -- so they do live in streams other than the Moormans!

I've discovered that this is Heptagenia marginalis, and one of the keys to identification is the "oblique" black lines on the margins of the abdominal segments (click to enlarge).  These hatch in July, August, and September.  Note that the wing pads on this one are quite a bit longer than those on the nymph that I found last week.

I also found more Whirligig beetles, some Dryopid beetles (on leaves and pieces of bark), lots of netspinners and fingernet caddisflies, and a handful of small minnow mayflies.  All of the small minnows were Baetis in terms of the genus.  Earlier in the summer, I found both Acentrella and Baetis nymphs here: the Acentrellas seem to be gone (they were looking pretty mature back in June).  A couple of pix (note the three tails).

I also found one spiny crawler, genus Serratella -- but the photos I got aren't really worth showing.
Below, Buck Mt. Creek in the low flow of summer.

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

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:  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.

Tuesday, July 26, 2011

The "Final" Flatheaded Genus: Heptagenia!

Finally.  The flatheaded mayfly (family: Heptageniidae), genus Heptagenia.  I was beginning to worry that I wouldn't find them this summer.  I found some last summer (August) in the Moormans River (off Free Union Road), and sure enough, that's where I found them today.  I've never seen very many; I've only seen them in summer (note that this is a "young" one -- short wing pads); and this is the only stream in our watershed -- so far -- where I've seen them.  Isn't it a beauty?!

The gills on the nymphs of this genus look exactly like those on genus Leucrocuta.  The difference?
Gill #7 on a Heptagenia nymph has fibrilliform (feathery strands behind the gill plate); those on a Leucrocuta nymph do not.  You can actually see the fibrilliform in this live photo (click on the photo to enlarge it.)  It's also true that Leucrocutas are very small nymphs; Heptagenias can be pretty big.

If that doesn't work, here's a microscope shot from one of the nymphs that I found last year.

My guess is that this genus matures in mid August through mid October -- but I'll have to come back to see.  (I see that Knopp and Cormier, Mayflies, p.150, note a hatch of Heptagenia solitaria from the beginning of August through the end of October -- but H. solitaria is noted as a Western species.)

I found two other unusual things at the Moomans today.  One -- a yellow-orange Common netspinner, genus Hydropsyche.  I've never seen one this color before, and I got a really good close-up.

The other oddity is this Pleurocerid snail with its head sticking out, on which you can see the eye!  The eyes on a snail are located at the base of the tentacles.  (On snail anatomy, see Douglas Grant Smith, ed., Pennak's Freshwater Invertebrates of the United States: Porifera to Crustacea, pp. 328-330 -- in the 2001 edition.)

Pleurocerid snails are the most common "gilled" snail we find in our streams.  For some reason, the pointed top end of the shell is always broken off (or just flattened?)

There were other treasures today: lots of small minnow mayflies (genus Acentrella);  a number of young Acroneuria common stoneflies; a Serratella spiny crawler (which I didn't notice until I looked at things with my microscope when I got home!); quite a few brushlegged mayflies; and a couple of Whirligig beetles.

But the prize of the day was that Heptagenia flatheaded mayfly -- and check out the length of those tails!

Wednesday, July 20, 2011

Our Summer Spiny Crawler: Genus Serratella

My main goal this summer is to find and photograph those nymphs and larvae that are only around this time of year -- e.g., damselflies, dragonflies, Long-horned case-maker caddisflies, and the Macrostemum common netspinners that I found on Sunday.   This morning, for the first time this summer, I found a few spiny crawler mayflies that were genus Serratella, and I found them in the Rivanna River in Darden Towe Park, one of the few places I saw them last summer.

The spiny crawlers we saw throughout the spring in HUGE numbers were genus Ephemerella.  They are plentiful, and they tend to hatch in May and June, and they account for some major hatches that are much anticipated by fly fisherman: E. invaria and E. rotunda become "Sulphur Duns," and E. dorothea hatches as the "Pale Evening Dun."  Serratella nymphs are not plentiful, we see them sporadically throughout the summer, and they are of little or no interest to fly fishermen.  They are also small, probably 1/2 the size of the spring Ephemerella.  And, they are drab in appearance -- dark brown or black.  Ephemerella nymphs -- olive or brown -- are richly patterned.  For example, this one that I found in late May.

Anatomically, however, the two genera are similar in constitution, in that the gill structure is exactly the same.  On both, there are gills on top of abdominal segments 3-7, though the gill on segment 7 is usually partially obscured by the gill on segment 6.  Here's a good picture of that from one of the Serratellas that I found this morning.  The second photo shows the actual "gills" under the gills.

However, the tails -- or "cerci" -- differ.  Ephemerella tails have "intrasegmental setae" -- i.e. they're very hairy; Serratella tails have whorls of spines at segmental joints but little or no intrasegmental setae.  Compare.

Ephemerella cerci:

Serratella cerci (also click on the photo at the top of the page to enlarge it):

So nice to see this genus around again for the summer.

The other insects of interest that I found this morning -- I can't get real excited about "tons" of netspinners, some Maccaffertium flatheads, and a few small hellgrammites! -- were small minnow mayflies, quite a few of them actually.  They were all Heterocloeon in terms of genus -- in fact they were, again, Heterocloeon curiosum.   Some nice pix:


We identify Heterocloeon nymphs by 1) the two tails (vs. three), and 2) by the gray pigment in the center of the gills (that's actually pretty clear in all of the photos above -- click on them to enlarge them.)
Here's a close-up of the gills on one of these nymphs.

And we know they are species curiosum because they have "procoxal gills," tiny finger-like gills that stick out from the base of the front legs.

One final photo.  This is another Heterocloeon curiosum small minnow mayfly, but a younger one with somewhat muted colors.

It's beginning to look like the small minnows that flourish in the Rivanna River throughout the summer are, for the most part, Heterocloeon curiosum.  Remember, this is what I found last week in the Rivanna at Crofton as well.   But, this is just an hypothesis to be tested.

Tuesday, July 19, 2011

The Trumpetnet Caddisfly (Polycentropodidae): Genus Polycentropus

I went to the Doyles River in Doylesville last week -- but I didn't find anything new or exciting.  There are still some common stoneflies here, genus Perlesta, and I also saw a young Acroneuria.  Lots of netspinners, fingernets, and flatheaded mayflies (genus Maccaffertium, and a few Epeorus vitreus).  I also found a few small minnow mayflies, genus Baetis, and I'll show you a photo of one of those in a minute.  But the water was low, and with the heat we're having this week, it's bound to drop even more.  So, for the moment, I think I'll stick with the big river -- the Rivanna itself: that seems to be where the action is at the moment.

But I did find the interesting caddis larva in the photo above.  This one fooled me.  It was long, maybe 3/4", and big and orange.  And with abdominal segments that are pretty constricted, my guess at the stream was that it was a freeliving caddis.   However, when I downloaded my photos at home and noticed the gray "freckles" (muscle scars) on top of the head, my thoughts went right away to Polycentropodidae, a "trumpet net" caddisfly larva.  There's only one way to know that for sure -- you have to check the shape of the fore trochantin using a microscope.  The fore trochantin (the joint where the front leg meets the body) should come to a sharp point -- sort of looks like a pick-axe.

So, no doubt about it: it was indeed a Polycentropodid.  What about the genus ID?  That's also easy to determine using a good microscope.  This one is Polycentropus.  How do we know?  The "suture" on the anal proleg of Polycentropus consists of a black "X".

Polycentropodids, by the way, have a tolerance value of "6.0" in the VA DEQ list of tolerance values: in the NC DWQ list, the genus Polycentropus comes in at "3.1".    Since I was thrown off by the color, let me remind you of what they normally look like: this is a photo of one from the Doyles, that I posted back at the beginning of May.

Two more photos.  The first, a lovely little flatheaded mayfly, Epeorus vitreus.  We find these all summer long in our "good," cold water streams -- though never in very large numbers.

The other, a small minnow mayfly, genus Baetis.  I don't know the species.  But I've been finding this species in a lot of streams now (at least I think it's the same species I'm seeing).  It's very small -- every one I've seen has been small -- and not very colorful.  But  they may be small and lacking in color because they're immature.  Note that the wingpads are not very long.

Tolerance Values and Monitoring the Health of Our Streams

                              (The Rivanna River below Palmyra, VA in Autumn)

Let me begin by showing photos of a few insects, most of which I can identify to the level of species, then note, 1) the current "tolerance value" used for that taxon by VA DEQ (the Virginia Department of Environmental Quality), and 2) the value assigned to that taxon in the new list of tolerance values posted by the NC DWQ (North Carolina Division of Water Quality).  After that, I'll discuss the possible significance of these discrepancies.  Please note that, at the moment, VA DEQ bases tolerance values on "family level" ID; NC DWQ goes to the level of species.

I. Baetidae (small minnow mayflies)

1. "Probably" Acentrella nadineae; Buck Mt. Creek, 3/1/11
VA DEQ tolerance value, "4.0"
NC DWQ tolerance value, "1.9"

2. Heterocloeon curiosum, Rivanna River, 7/11/11
VA DEQ tolerance value, "4.0"
NC DWQ tolerance value, "2.1"

3. Baetis pluto, Buck Mt. Creek, 6/10/11
VA DEQ tolerance value, "4.0"
NC DWQ tolerance value, "3.4"

4. Acentrella turbida, Buck Mt. Creek, 10/25/10
VA DEQ tolerance value, "4.0"
NC  DWQ tolerance value, "2.0"

II. Odonata, Gomphidae (Clubtail dragonflies)

1. Hagenius brevistylus, Rivanna River, 7/11/11
VA DEQ tolerance value, "1.0"
NC DWQ tolerance value, "4.4"

2. Ophiogomphus, Buffalo/Roach River, 7/6/11
VA DEQ,tolerance value, "1.0"
NC DWQ tolerance value, either "undetermined" or "5.9"

III. Common Netspinners (Hydropsychidae)

1. Cheumatopsyche, Buck Mt. Creek, 3/18/11
VA DEQ tolerance value, "6.0"
NC DWQ tolerance value, "6.6"

2. Diplectrona, Moormans River tributary, 3/4/11
VA DEQ tolerance value, "6.0"
NC DWQ tolerance value: Diplectrona metaqui, undetermined; Diplectrona modesta, "2.3"

3. Macrostemum, North Fork of the Rivanna, 7/17/11
VA DEQ tolerance value, "6.0"
NC DWQ tolerance value, "3.4"


Let me note a few things before I comment on the possible significance of the data cited above.  1) Virginia DEQ is in the process of developing a new list of tolerance values for benthic macroinvertebrates based on genus level ID.  My understanding is that those values will be put into place in determining "scores" for the health of our streams sometime within the next 5 years.  2) Tolerance values are only one of the things that are used in determining scores for streams.  The "metrics" used for these calculations are complicated, and you can see how complicated by viewing the slide show put together by StreamWatch ( indicating how they go about it.  I urge all volunteer monitors to review that information.  3) The genus tolerance values used by the state of Virginia might not be the same as those used in North Carolina.  Tolerance values for stream taxa, apparently, vary with locale.  I don't quite understand why that it so -- but it is.  And 4) the data presented above is for -- what? -- 8 species.  Any differences these figures might make in scores could well be offset by different values for other taxa.  I.e. "new" scores developed by using new tolerance values might not vary that much from the current scores.

All of that being said, it seems clear that more exact tolerance values for taxa will lead to more accurate stream assessments -- something all of us want to see.  At the same time, going to "genus" or even "genus and species" tolerance values could certainly affect the role played by amateur volunteers in monitoring the health of our streams.   Family ID of macroinvertebrates isn't easy; genus ID often -- perhaps most of the time -- requires microscope work in a lab; and species ID is a job for the pros.
Those of us who love to sample in streams may well have to find a new way to participate in keeping an eye on the health of our streams.  But, all of this remains to be seen.