I Went, I Found, I Came Home

I went to the North Fork of the Rivanna this morning in search of one thing: I also found other good things, but this is the larva that I was after.  Common Netspinner (Hydropsychidae), genus Macrostemum.  Very few volunteer samplers ever see this one since it's not all that common -- in our watershed, that is -- and it's only here from mid-summer through early fall.  Another look.

Check out the head.  It slopes down from the back to the front -- in fact, it's a little caved in.  But that's not easy to see without magnification, and I've worked with monitors in the past who had no clue what this was -- despite the obvious frilly abdominal gills.  The other problems with identifying this as a netspinner are that it's an odd shade of green, and, it's big and fat, considerably longer and fatter than the netspinners that we commonly see.

For keying this out, let's use Peckarsky (Freshwater Macroinvertebrates, p. 101).  There we read: "Head with a broad, depressed, flat, dorsal area surrounded by an extensive arcuate carina; anterior margin of tibia and tarsus of foreleg with a dense brush of pale setae."  I was able to get a microscope shot that shows us both of those features.

Very, very odd-looking critter as netspinners go.  And it's less tolerant than the two genera we most often see (Cheumatopsyche and Hydropsyche).   In the latest list of tolerance values posted by the North Carolina Division of Water Quality, Cheumatopsyche netspinners have a value of 6.6; Macrostemum netspinners come in at 3.4.  One more photo of a Macrostemum larva since they aren't that easy to find and not that easy to photograph either!

The vegetation growing on rocks in the North Fork was absolutely crawling with netspinner larvae -- only 4 of which were genus Macrostemum.   If I lifted a rock out of the water and let it sit a few seconds with the vegetation exposed to the air, I'd see netspinner larvae wiggling all over the place.  I certainly saw hundreds of larvae today, possibly thousands.   I'm convinced that the main hatch of netspinners in this part of Virginia occurs in the fall.

A few other nice photos to look at, though I don't want to detract from the focus of today's entry.
There were also a lot of brushlegged mayflies hiding away inside the vegetation on top of the rocks.
A lot.  And they were pretty mature.  I'd expect them to hatch by the end of the summer.  Here's a pretty good shot (note the dark wing pads).

There were also flatheaded mayfly nymphs present -- all Maccaffertium -- and I found three small minnow mayflies, 1 was a small three-tailed Baetis, the other two were Heterocloeon curiosum, the same species I found in the main stem of the Rivanna last week.  The deciding factors: a circle of gray pigment in the center of each of the gills, and "procoxal gills" --  fingerlike gills sticking out from the base of the front legs.  Got a good microscope photo of that.

And, I found yet another Hagenius Clubtail dragonfly (I understand from the folks at Bugguide.net that this is Hagenius brevistylus).  I may have to revise my thinking that these are rare in our streams.  By the way, they are always tangled up in vegetation and sampling with the protocol that's normally used would not shake them loose.  It's unlikely that volunteer groups are going to see them.

And finally, I found an unexpected treasure: a "Whirligig beetle" larva -- family Gyrinidae.  I have never seen very many of these -- a few in Buck Mt. Creek, a few in Mechunk Creek, and now one here in the North Fork.  And this was a big one -- I'd say about 1 1/4" in length -- and in its fully mature very bright colors.

All in all, a nice summer day at the stream.

The "Needle in the Haystack": A "Long-horned" Case-maker

This was a bonus today -- though I've been hoping to find some.  That little insect sticking its head out of the case that's attached to that piece of vegetation is a Leptocerid caddisfly larva -- a "Long-horned" case-maker.  I'm pretty sure the genus is Nectopsyche (see the entry of 1/26 on Leptocerids)-- but I couldn't get it out of its case, so I can't really confirm that.   If you can't see the larva, here's an annotated version of the picture above (and I encourage you to click on the photo to enlarge it.)

I usually find these in the Rivanna, and that's where I went this morning -- to the boat put-in below the bridge at Milton.  But, these are extremely hard to find, and it is indeed like looking for a needle in a haystack.  Leptocerids -- this genus at least -- attach their cases to the grass or algae that covers the rocks in the Rivanna each summer.  This vegetation is long (2-3"), dense, and gnarly.  And these cases are tiny -- you'd never see them if you didn't know what to look for.  Here's another shot of this insect.

I hope to find more of these throughout the summer (and I should) -- and with luck I'll find some that are a bit bigger than this one!

But I found other treasures today.  Such as....

...this beautiful Emerald Dragonfly (family Corduliidae).  In Voshell (Freshwater Invertebrates), this would be called a "Skimmer Dragonfly" (pp. 126-127), for which he gives the family name Libellulidae.  But Libellulidae and Corduliidae as dragonfly families can be distinguished: in nymphs of the family Libellulidae, the "crenulations on the distal margin of the palpal lobes are usually separated by shallow notches (Merritt, Cummins, and Berg, Aquatic Insects of North America, p. 249), while with those of the Corduliidae family the crenulations are separated by deep notches (same source, p. 246).   Here's a microscope view of the notches in question -- and they're deep.  (The definition of "deep" is "one-fourth to one-half as high as long" (same source, p. 246).

Some other treats -- damselfly nymphs, both broad-winged and narrow-winged, so a good chance to see how different they are in appearance.

Broad-winged (Calopterygidae)

and Narrow-winged (Coenagrionidae)

It's not very difficult to tell them apart.  Note the difference in the antennae.  With Calopterygidae, the first segment of each antenna is longer than the other segments combined.

One more treat -- a "baby" Hellgrammite.  This one was really, really, small -- about 1/8" long.  It has not been here in this world very long.

If there's any doubt about the identification, you simply have to look at the anal prolegs: each proleg has two claws at the end.  And here is a microscope photo of that.  (Oh.  Stream monitors should know that when hellgrammites are this small, they can be confused with netspinners.  If they look a little bit off, be sure to look at them with a loupe.)

(Below -- another look at our Emerald Dragonfly.)

Pursuing Dragons and Damsels: Off to the Rivanna

I've been hoping to find -- and photograph -- more dragonfly and damselfly nymphs, so this morning I went to a place on the Rivanna where I've found a lot of them before.  I managed to find two "Narrow-winged" damselflies (family: Coenagrionidae) and another Hagenius clubtail dragonfly nymph.

The narrow-winged damsel in the photo above is one of the prettiest specimens I've ever seen.  For beginners -- damselfly nymphs have three "tails" like most mayfly families and genera, but the "oar-like" or "paddle-like" shape of the tails makes them easy to distinguish.  And, in reality, these "tails" are not "tails" at all; they're "caudal filaments" -- essentially gills, i.e. they use them to breathe.

Narrow-winged damselflies are easy to ID at the streams, at least when they're as big as the one in the photo above (3/4" - 1" in length).  Flip them over and look at the "chin" (as it were), the "prementum".
It should look like this.

It's wide at the top and narrow at the bottom.  The nymphs that I found today were Argia in terms of the genus.  To determine this, we have to look at the palpal lobes, on which we find in Peckarsky (Freshwater Macroinvertebates, p. 46): "Distal margin of each palpal lobe produced into 3 pointed hooks, middle one shorter than end hook and usually about 1/2 as long as movable hook."  Have a look.

Narrow-winged damselflies are "tolerant" insects.  In the new list of tolerance values used in North Carolina, Coenagrionids, those with tolerance values that have been determined, run from 8.3 to 9.5.  But it's good for us to remember that finding "tolerant" insects in rivers and streams does not necessarily mean that that body of water is somehow "polluted" (through siltation, sewage, etc.).   Insects that are mature or maturing during the summer in this part of the country have to be tolerant of reduced levels of oxygen in the water because of high water temperatures.   These are insects that have ways to adjust to the lower oxygen levels -- e.g. they're smaller in size than insects we find the rest of the year, or, like common netspinners, they have numerous gills so they can suck up all the oxygen that they can find.

The dragonfly nymph that I found was an Hagenius nymph.  I have posted photos of this genus before.
It's a "clubtail" dragonfly (a Gomphid --look at the size and shape of the antennae) that's distinguished by its flat, circular body.  This one was about the size of a penny -- maybe a little big bigger.  (If you click on the photo to enlarge it, you can see the tiny 4th segments of the antennae.)

Looks nothing at all like the clubtail we saw last week that I found in the Buffalo/Roach River.

What else did I find?  Lots and lots of common netspinners.  On rocks that were covered with the tangled grass (algae?) that grows here in the summer, they were simply crawling all over the place.  It's like there has been a population explosion of netspinners and fingernets in all of our streams, but the Rivanna in summer has extremely high numbers of both.

I also saw flatheaded mayflies, brushlegged mayflies, and small minnow mayflies.  (The Rivanna in summer also has large numbers of small minnow mayflies.)  Here are a couple of photos (two different nymphs).

Both two-tailers, so in terms of genus they're either Acentrella, Heterocloeon, or Plauditus.  The gills on the first nymph seem to have pigment at the center, so I decided to have a closer look with my microscope.  And, it turns out that these Baetids are not only Heterocloeons, they're Heterocloeon curiosum!  That's because they have "procoxal gills" -- little finger-like projections that stick out from the base of the front legs.  Here are pictures of the pigment in the abdominal gills and then one of the procoxal gill.

(Photo below -- the other narrow-winged damselfly that I found this morning.)

Too Damn Hot! For Photos, That is, Not For Insects

I sort of hit the wall today.  I went to Buck Mt. Creek this morning.  I had no problem at all finding insects -- taking photos of them was a totally different matter.  It's hot and humid in central Virginia, though it's supposed to cool down by the end of the week.  So, when I tried to take photos this morning, my face was so hot that my camera viewfinder always steamed up: I couldn't tell if anything was in focus.  Ah the joys of entomological work in the summer!

I found the usual, the same insects I've been seeing for the last 2-3 weeks -- flatheaded mayflies (Maccaffertium, Leucrocuta, and a couple of Epeorus); small minnow mayflies (both Baetis -- in the photo above -- and Acentrella); Netspinners and Fingernet caddis larvae.  I saw a lots of fingernets on the bottoms of rocks today, but I've seen that before in July in this particular set of riffles.  I also found a few small common stoneflies (Acroneuria), and -- as you can see from the photo above -- one "trumpetnet" caddisfly larva (Polycentropodidae).  Note the "freckles" or "muscle scars" on the head.
I also had a spiny crawler  -- but it disappeared by the time I took the few photos I got -- and one tiny, Clubtail dragonfly -- that too disappeared.

Let's hope for better results at the end of the week.  By then, I should be able to get into the Rivanna.

(Below -- a small minnow mayfly, genus Acentrella, tangles with a common netspinner caddis.  Note the "frilly gills" on the abdomen of the caddis.)

New Water: A Trip to the Buffalo/Roach River

It's time to be looking for insects in the Rivanna River -- but it's high, fast-flowing, and more than a little off-color.  Albemarle County is being hit almost daily with powerful storms that are putting down heavy rain in various parts of the watershed: all of this ends up in the Rivanna.

So, I decided to head north this morning and take a look at the Buffalo River, or the Roach River, or the Buffalo/Roach River -- suit yourself with the name.  I was hoping to find some damselfly nymphs -- I've found them here before -- but no luck with that venture.  Still, I did find a nice little Gomphid ("Clubtail dragonfly") -- genus Ophiogomphus (in the photo above).   It's the antennae -- not the tail -- that help us ID this nymph at the stream: they look like "clubs."  Each antenna has four segments.  But the long, fat part of the antenna is segment 3: segments 1 and 2 form the base of the antenna, and segment 4 -- if it is visible at all (it usually isn't without magnification) -- is "vestigial".  Here's an annotated form of this photo, pointing out the antennae (you can actually see segment 4 if you click on the photo to enlarge it) and the wing pads, which, note, are "widely divergent".  That's one of the features that makes this an Ophiogomphus Gomphid (see Peckarsky, Freshwater Macroinvertebrates, p. 48).

I also found another Darner dragonfly in the Roach: it was climbing around -- as they often do -- in a tangle of submerged twigs and leaves.

No "clubby" antennae on this one.  The antennae on all dragonfly nymphs save for the Gomphid, are long, slender, and multi-segmented.  Here's a microscope view of the Darner antennae.

The dominant taxa today?  Netspinning caddisfly larvae -- both common netspinners (Hydropsychidae) and Fingernets (Philopotamidae).  They were crawling all over the rocks when I turned the rocks over, and submerged root balls were loaded with them.

Fingernet caddis (genus Chimarra)

Common netspinner caddis (genus Hydropsyche)

I seem to see more netspinning caddisfly larvae in all of the streams that I sample in the summer than at any other time of the year.  I'm a little bit puzzled by this since most fly fishing hatch charts have fingernets and common netspinners hatching in mid to late spring.  At the moment, I can't really explain it.

For mayflies, I found both flatheads and brushlegged nymphs -- didn't see a single small minnow mayfly!  But I've found that in this river before.  This is a brushlegged stream, and I saw some really mature ones today, some with really dark wing pads.

The brushlegged species we find in the East is Isonychia bicolor, and Knopp and Cormier state that "Isonychia bicolor hatches appear from late spring to fall on East and Midwest waters (Mayflies, p. 85).
So, we can expect to see brushlegged nymphs, both immature and mature, for the next 3-4 months.

Two other photos.  A beautiful, fully mature, flatheaded mayfly, genus Maccaffertium, and a common stonefly, genus --what else?! -- Perlesta.  (I also found baby roach-like stoneflies and a few baby "Giants").

(In the photo below, the Gomphid and the flatheaded mayfly face off in the tray!)

Ventral Patterns and the Identification of Flatheaded Mayflies to the Level of Species

A short time ago -- on June 22nd -- I posted an entry on fly fishing and the major species of flatheaded mayflies.  Last night while surfing the web I discovered a web page that is extremely useful for those of us who wish to pursue this information.   The page in question has photos by Donald S. Chandler of a number of key flatheaded species, showing that the "ventral pattern" is crucial in species determination.
The website is "Discover Life," and the page in question is: http://www.discoverlife.org/mp/20q?search=Maccaffertium.

This morning, in viewing the "tummies" of the Maccaffertium nymphs in my reference collection, I discovered what appear to be five different patterns: I have no doubt what at least two of them are.  Chandler ID's the pattern above as that found on Maccaffertium vicarium nymphs -- for fly fisherrmen, the "March Brown" hatch that we anticipate every spring.   I think this was a nymph that I found on March 28th in Powells Creek in Crozet -- the one in the photo below.

This is a big nymph, and the "March Brown" is a big terrestrial mayfly.  Knopp and Cormier (Mayflies: An Angler's Study of Trout Water Ephemeroptera, p. 176) give a hatch range for M. vicarium of mid-May through mid-July here in the East (but the hatch might start even earlier in the southeast).

The other pattern I can ID for sure is this one:

This is Maccaffertium ithaca -- the "Light Cahill" for fly fishermen -- and this is one of the flatheads I found yesterday at the Lynch River.  Here's another look at that nymph.

This is an insect that hatches throughout the summer, normally from late afternoon until dark.  Knopp and Cormier (p. 176) give a hatch range for M. ithaca of mid-June through mid-August.  So, no surprise that the wing pads on this nymph are already quite long.

The patterns I found that I can't really ID for sure -- nor can I match them up now with any flatheaded photos I have that I can date.  Nonetheless, here they are.

1)  (This may be M. modestum which hatches from the beginning of June through the end of July.  Feel free to check this against the photo at the website noted above and let me know what you think.)

I should add that, if you click on the photo and look at the much larger image, you'll see that there are "posterolateral spines" (sharp pointed endings) on abdominal segments 7-9 (on this point, see p. 177 in Knopp and Cormier).  That feature is characteristic of M. ithaca, M. modestum, and M. pulchellum.  M. modestum and M. pulchellum hatch as the "Cream Cahill".  These hatch from the beginning of June through mid-October.

2) another pattern (also could be M. modestum)

3) and one more (is this a variant pattern for M. ithaca?)

4) Oops!  Sorry.  I do have another.  (Is this a young M. ithaca?)

I'll be checking out "bellies" on flatheaded nymphs from now on -- and matching them with the dorsal view of the insect.  I wish now that I had kept the other good sized nymph that I found yesterday.  But, alas, the one that got away!  There's just no end to the neat things that we can learn.

How to Ruin a River: A Summer Trip to the Lynch

Dam it up.  Someone has taken it upon themselves to ruin the Lynch River, or rather, to ruin the riffles that I like to sample.   Kids?  Teens?  The landowner?  Can't really tell you.  But they've stacked up the rocks at the head of what used to be very good riffles, creating pools out of nice, cascading runs.  Were this to create pools where someone could swim, I guess I could understand it -- but the water isn't that deep.  It's a shame.  And I'm not sure I see any reason to return to the Lynch -- at least to this particular site -- to look for bugs.  Alas!

But I looked in the few riffles that still remain, and I found pretty much the same thing I found yesterday at Buck Mt. Creek: flatheaded mayflies (genus Maccaffertium and genus Leucrocuta), and small minnow mayflies -- both Acentrella and Baetis.  The two biggest Maccaffertium nymphs that I kept for photos appeared to me to be different species.  Look at the square-shaped head in the nymph at the top of the page  (I think it's Maccaffertium ithaca -- the "Light Cahill") -- then look at the one in the photo below.

The head is more rounded off.  Here's a neat shot of both nymphs together, and the different shapes of the heads seems pretty clear.  Can't help you out with names for the species.

The Acentrella nymphs that I photographed might also be different species -- at least the colors were not the same.  Still, the darker one might simply be a more mature nymph of the same species.  Neither of these had the reddish/orange neck and spots that we found on the nymphs yesterday.  Still, the colors are stunning.  I'll simply post two photos of both of the nymphs I picked out.  On the last photo, one of the two small Baetis nymphs that I found is in the upper part of the photo.

I didn't see any stoneflies today.  Water pennies, netspinners, fingernets, and a few small brushlegged mayflies -- but the dominant taxa were the flatheads and the small minnow mayflies.

Next week I'll be off to the Rivanna River where I expect to see a good number of "dragons and damsels."