Genus ID of Stoneflies Found in Montana

Another rainy day; another good day to do some microscope work.

While fishing in Montana last month, I found two "common stoneflies" (Perlidae) that I had never seen in the East.  I got live photos of only one -- the one pictured above -- which the folks at Bugguide.net identified for me as Claassenia sabulosa.  With time on my hands today, I thought I might work through the genus ID of these two beautiful stoneflies.

For this purpose, the dichotomous key that I normally use for genus ID  -- Barbara Peckarsky, et.al., Freshwater Macroinvertebrates of Northeastern North America -- isn't sufficient: I'm looking at insects from Northwestern North America that, as I suspected, are not genera that we find in the East.  So, we have to use the "big book" -- R.W. Merritt, K.W. Cummins, and M.B. Berg, ed., An Introduction to the Aquatic Insects of North America, pp. 325-327.   The lastest edition, the Fourth Edition, published in 2008, has a mere 1058 pages of detail for the identification nymphs, larvae, and adults.

Let's get started.  Claassenia turned out to be very easy.  There are three features to look for and they're right at the start of the key.  Two microscope photos are all that we need.  And in our key, we turn to p. 325.

51 Occiput with transverse row of regularly spaced spinules
or
51' Occiput without spinules, except possibly laterally near the eyes, or with a sinuate, irregularly spaced spinule row

There is a clearly defined row of "regularly spaced" spinules.

52 Two ocelli
or
52' Three ocelli

There are three.

53 Ab [abdominal] terga with more than 5 intercalary bristles ...... Claassenia
or
53' Ab terga with no more than 4 intercalary bristles

There are "lots" of intercalary bristles, those little dark brown spikes on the top of each abdominal segment.  So, this is clearly a Claassenia nymph.  Another look (and note the tiny Perlodid stonefly taking a ride on the Claassenia's cerci!)

ID of our second nymph proved to be more complicated, involving a number of steps.  But let's begin with a photo of the bug.

I am so sad that I have to use a photo of the preserved insect.  I found this one at the end of a day of fishing the Blackfoot River: I had a vial to preserve it -- I did not have my camera with me!  So, we have to make do.

Again, let's begin with a close-up view of the head.

So remember our options are, 51, an "occiput with [a] transerse row of regularly spaced spinules," or, 51', no spinules, "or with a sinuate, irregularly spaced spinule row."  Bingo!  That's what we have.

From 51' we move to 55 and 55', where we have to decide between "no spinules" or the "sinuate, irregularly spaced row."  Since we have the "sinuate row," we move to 56.

56 Ab terga with fewer than 5 or no intercalary bristles......Hesperoperla
or
56' Ab terga with more than 5 intercalary bristles

Again, there are a lot more than 5.  We move to 57 and 57'.

57 ...posterior fringe of Ab terga mostly of short setae whose length is about one-fourth the length of Ab segments
or
57' ...posterior fringe of Ab terga with numerous long setae whose length is three-fourths or more the length of Ab segments....Attaneuria


The setae are pointed out in the photo above, and they are clearly no more than one-fourth the length of the segments.  We move to 58.

58 Cerci without a dorsal fringe of long silky hairs
or
58' Cerci with prominent dorsal fringe of long silky hairs

You'd have to say that fringe is pretty prominent!  We move to 59.

59 ...Ab7 sternum [the back side of abdominal segment 7] usually with incomplete posterior fringe
or
59' ...Ab7 sternum usually with a complete posterior fringe....Calineuria


We flip our nymph onto its back.

Segment 7 does have a "complete" fringe; segment 6 does not.  Our stonefly is genus Calineuria.  Now if I only had a "live" photo.  Have to wait for next year's trip back to Missoula!

Below.  Fishing on the Blackfoot River, north of Missoula, Montana.

Found! Odontoceridae -- the Strong Case-maker Caddis

One of my friends who lives in Sugar Hollow told me last week that she had found Odontocerids in the North Fork of the Moormans.  She told me exactly where to go -- I went there this morning-- and sure enough, there they were!  They were easy to spot since they were crawling around on top of the rocks, and their light-colored cases stood out in contrast to the Greenstone composition of the rocks underneath.

The "Strong Case-maker" is not easy to find, and that for two reasons.  1) This is a critter that is extremely intolerant of stream impairment: Psilotreta libada -- probably the species we see -- has a TV of 0.5 (North Carolina Division of Water Quality).  So, if you want to look for this caddis in our part of Virginia, you'd better head to the clean, cold, rocky streams at the base of the Blue Ridge, streams like the North Fork of the Moormans and the Rapidan River.  2) The other thing that makes this one a problem to find is the fact that it apparently spends most of the year in the gravel of the substrate.  Two exceptions: for some reason, they tend to crawl around on the rocks in the fall (September and October), and their cases can be found on the rocks in the late spring right before they hatch out (in May and June).  (For a full discussion of Odontocerids and their importance for fly fishermen -- the "Dark Blue Sedge", be sure to read Thomas Ames Jr.'s Caddisflies: A Guide to Eastern Species for Anglers and Other Naturalists, pp. 209-214).)

I can't say for sure that the larvae I found were Psilotreta libada -- that's just a hunch: I do know for sure that the genus is Psilotreta.  This is easy for us to determine.  On the Psilotreta larva, the "anterolateral margins of [the] pronotum [are] produced into long, sharp, forward-projecting points" (Peckarsky, Freshwater Macroinvertebrates, p. 118).  And here is what those points look like in a microscope view.

The "Strong case-maker," by the way, clearly deserves its name.  I've tried to break these cases using my tweezers: can't be done.  Ames explains this in the following way: "The larvae spend at least a part of their lives out of harm's way, burrowed into moss or in the sand, silt, and gravel beneath the cobble of cool streams.  As protection against the grinding motions of the substrate they apply extra silk as mortar between the sand and tiny pebbles that make up their cases.  The result is the curved, crush-resistant, cylindrical case that gives the family its nickname." (Caddisflies, p. 209)

Cases are sometimes straight and tube-like, but they're often tapered.   In the photos I took this morning, I've got one of each.  Here are some of the photos for you to enjoy.  The orange and black striped head, by the way, can give this one away if you see it crawling around in your tray.

E. subvaria and E. dorothea: Two Spiny Crawlers of Great Interest to Fly Fishermen

I've decided to try my hand at species identification of some of the spiny crawler mayflies (family: Ephemerellidae) that we find in our streams, and I've identified two that are of great interest and importance to fly fishermen.  One -- pictured above -- is Ephemerella subvaria, which provides us with the "Hendrickson" hatch in spring, the other -- and pictures of that in a moment -- is Ephemerella dorothea which gives us the "Pale Evening Dun (PED" hatch in early summer (mostly in June).

When I lived in Vermont, the Hendrickson hatch was one of the big events of late spring -- well, for fly fishers that is -- often occurring the last two weeks in May.  It's a big fly, easy to recognize, and provides great dry fly fishing (one of the reasons we like it so much!).  In our area (Virginia. that is), hatches are apt to occur earlier in the year, a fact that is noted by Knopp and Cormier (Mayflies, p. 195).  They point out that in the the southern Appalachians, the Hendrickson hatch "typically peaks in mid-April."  That very clearly accords with my findings.

My first sighting of this nymph -- and I have only seen it in that Virigina "Mecca" of trout fishing, the Rapidan River -- was on January 19th.

And I saw it again on February 23rd:  note how the wing pads have lengthened.

And my last sighting was on March 24th, the nymph that's featured at the top of this page.  That one was close to hatching -- it almost looks like the wings are partly revealed.

How do we identify this as E. subvaria?  First of all, a word of caution: not all E. subvaria nymphs will have these same colors and patterns.  As always, ID requires matching of key anatomical features.  That being said, one of the features we use for ID is the markings on the tibiae and tarsi: there's banding that is dark brown or black.  No need to use the microscope; we can see that in our photos.  But the two other features do require microscope photos.  They are: 1) sharp, paired "tubercles" on the back edges of abdominal segments 2-9.

The tubercles on 2 and 9 may be hard to see in this photo -- the rest are clear as can be.  And the other feature that we need to see -- posterolateral projections (sharp edges) on terga 4-9.

And there we have it: E. subvaria, the "Hendrickson" to fly fishermen.
_________________________________________

And now, for E. dorothea, the "Pale Evening Dun".

This is the most common spiny crawler we see in our streams, showing up in the hundreds and thousands in the spring -- March, April, and May -- with peak emergence occurring from mid-May to mid-June.  On E. dorothea, Knopp and Cormier (Mayflies, p. 207) note that they are "reliable June emergers," but that in the "warmer southerly trout waters [they] may produce hatches as early as the first weeks of May."

One of the first sizeable E. dorothea nymphs that I saw was at the Whippoorwill branch of the Mechums: that was on March 18th.  (The one in the photo above is from April 14th, Buck Mt. Creek.)

And the last E. dorothea I saw was in a small, clean and cold, tributary to the Moormans on May 18th, and you can tell from the rich colors and patterns that it's fully mature.

What are diagnostic traits for this spiny species?  Some are really obvious from our photos: the abdominal terga are brown, covered with light freckles and pale dots, and, there are no tubercles on the terga.  Also, there is a visible, pale stripe running from the head to the tail of the nymph.   Again, for the other key features -- there are two -- we have to use microscope photos.

1) As with E. subvaria, there are "posterolateral projections" on abdominal segments (terga) 4-9.

2) But, unique to this species, are the "stout setae" -- short hairs -- on the edges of those posterolateral projections.

Voila!  E. dorothea, or the "Pale Evening Dun."

Two final notes.  1) For tolerance values -- the North Carolina Division of Water Quality assigns a 3.3 to E. dorothea, but feels it does not have enough evidence to decide a TV for E. subvaria.  And 2) for good photos of the "adult" terrestrial forms of these insects, I suggest you look at troutnut.com.

E. subvaria (Hendrickson):  http://www.troutnut.com/specimen/494
E. dorothea (PED):  http://www.troutnut.com/specimen/743

(Below, E. dorothea nymph posing next to a caddis larva case (Lepidostomatid) -- tributary to the Moormans River, photo taken on May 6th.)

Some Surprises at the Rapidan River

It's one of those days when I'm not really sure where to begin.  I went to the Rapidan River in search of "Strong Case-maker" caddisfly larvae (Odontoceridae) since I found them here at this time last year.  Did not find a one.  But, I had a couple of real nice surprises that made the trip very worthwhile.

Above -- a very small Perlodid stonefly, genus Isogenoides.  This is the first time I've seen this genus here in the East (I've seen it before in Montana).  Very exciting.  It seems very early to find a Perlodid stonefly, but perhaps this is a genus that hatches sometime in the winter.  I'll have to read up.  Keys to identification: 1) this one has "submental gills"; and 2) the "median ridge of the mesosternum extends anteriorly beyond the fork of the Y to the transverse ridge" (Peckarsky, Freshwater Macroinvertebrates, p. 71).  Here are the microscope pictures for confirmation.

What a treat!  Here's another look (at what I thought was just another "tiny" common stonefly!)  Beautiful colors.

The other bug that surprised me was this tiny spiny crawler nymph, genus Ephemerella.

That's the edge of a "humpless case-maker" caddisfly on the left -- to give you some idea of how small this is.  But look at the colors (click on the photo to enlarge).  They may show up better still in the microscope photo I took when I got home.

Those colors are very, very unusual, and it's very odd to see even minute spiny nymphs at this time of year.  But, let's go back and remember the spiny crawlers I found here -- in the Rapidan River -- in the winter, on January 19th of this year, to be exact.  And I continued to find this colorful species here through mid to late March.  This is apparently Ephemerella subvaria.

I would not be surprised to find out that the nymph that I found today is the same species (E. subvaria) as this beauty I found in early winter.  Again, this is something I have to research when I have time.

That's all I have for "surprises," but I did get some other nice photos of some of the insects that I normally find when I come to this stream: 1) fingernet caddisfly larva, genus Dolophilodes; 2) common stonefly, genus Paragnetina; and 3) a humpless case-maker caddis (Brachycentridae), genus Brachycentrus.

Dolophilodes

Paragnetina

Brachycentrus Brachycentridae

The Brachycentrids I find in this river make beautiful cases -- always richly colored.  And, this Brachycentrid actually came far enough out of its case to let us see why it's a Brachycentrus.
Brachycentrus nymphs have four sclerites (brown spots) on their fleshy mesonotums.  In the photo below, the two on the side might not be easy to see; the two in the middle are very clear.  (Please click on the photo to enlarge it.)

For an overview of the insects I found today in the stream -- 1) The common stonefly was probably the dominant taxon, genus Acroneuria and genus Paragnetina, all different sizes.  2) I found the odd common netspinner and 2-3 fingernet caddis.   3) I saw a fair number of flatheaded mayflies -- Epeorus, Maccaffertium, and Heptagenia, lots of them were very tiny.  4) I only found 3-4 humpless case-makers.  5) I saw many, many tiny insects (mayfly nymphs, I think) that were so small there is no way I could pick them up with my tweezers.  And 6) in addition to the "surprise" spiny crawler, I found 2-3 small minnow mayflies, all Baetis intercalaris, as in the photo below (key = the "parentheses" marks at the top of each abdominal segment).

Heptagenia marginalis -- Finally, One That's Fully Intact!

Our beautiful "summer" flatheaded mayfly -- Heptagenia marginalis -- and one with all of its legs and tails!  If you've ever tried to pick up flatheaded mayflies with tweezers, you'll know that they start falling apart the minute you look at them!  Off comes a leg -- or two -- or one of the tails is broken.  So I was thrilled to finally get a photo of one of these beauties on which nothing is missing.  I also found one that had just recently molted.  Note the light color: it takes awhile for the pigment to darken.  Black, oblique lines on the sides of the abdominal segments help us to ID this particular species.  Pretty clear on this nymph.

Also note that the wing pads on both of these nymphs are starting to look pretty long.  Since most guides say that Heptagenia marginalis usually hatches by the end of August or start of September, these two are a little behind!

I took a quick trip to the Rivanna River at Darden Towe park this morning in full knowledge that there, at least, I was bound to find moving water.  I also had hopes of finding more Leptocerid cases (Long-horned case making caddisflies).  But I didn't: they're very hard to see since they look like tiny bumps on branches.  In fact, here too, as at Buck Mt. Creek, I didn't find a whole lot of insects.  The summer netspinners are pretty well gone.  I saw quite a few common stoneflies, mostly small, and a lot of hellgrammites -- small, large, and all sizes in-between.  Then, too, there were quite a few flatheaded mayflies, most of them Maccaffertium in terms of the genus.  I did bring a few of those home to see if I could work out the species ID.

I also found a couple of small minnow mayflies -- and I do mean a "couple".  One was Acentrella nadineae, the other Baetis intercalaris.  Pictures below.  (Shouldn't these all be hatched by now?)

Acentrella nadineae

Baetis intercalaris

Still no sign of our "autumn" small minnow mayfly -- Acentrella turbida -- but I think it's still a little bit early for that nymph to show up.  Below, another look at Heptagenia marginalis.  May be the last one I see until next year at this time.

Break Time: No Water, No Interesting Insects

This photo was taken last year on 9/22.  Things aren't quite this bad at the moment -- but I could not find running water in the Lynch River this morning.  And, where I can find running water -- e.g. Buck Mt. Creek -- there really aren't any interesting things going on in the world of bugs, nothing new to see.

So -- I'll be taking a break from the streams, but I'll be rifling through riffles again at the end of September and into October.  There are still a number of insects I'm hoping to find and photograph before the end of the year, insects that we typically see in the fall.  My list: 1) small square-gill mayflies (Caenidae), 2) rolled-winged stoneflies (Leuctridae), small minnow mayflies -- Acentrella turbida, and 4) strong case-maker caddisfly larvae.  Anything else that I find will be a bonus.  I'm also anxious to see if we have any other species of small minnow mayflies that inhabit our streams in the fall.

But for now I'll be waiting for rain, and waiting for the seasons to change.

A Slow Day at Buck Mt. Creek

Has to be a slow day when I start off with pictures of an adult Dryopid beetle!  What's odd to me is that when I found these in samples the last couple of years, they always looked totally black: not so in a close-up photo.  They actually have a very nice pattern.

The Dryopid beetle is distinguished from a "Riffle Beetle" (Elmidae) by the size -- Dryopids being the larger, around 1/4" in length -- and by the antennae.  Dryopid antennae are short and stubby vs. the "normal" antennae of the Riffle Beetle (which are segmented and red).  Here's a good look at the Dryopid antennae.

I really had to "hunt" for insects today: on a lot of rocks I found nothing but snails.  Obviously, I was spoiled by the rocks in Montana which often had 20-30 insects calling them home.  And, in all honesty, I didn't find a whole lot today.  The dominant taxon?  The "common stonefly,"  genus Acroneuria.  Actually, they're already quite a bit bigger than they were at the start of the summer -- but they won't hatch until early summer next year.  Acroneuria abnormis.

I saw flatheaded mayflies, but not in great numbers, and they were all genus Maccaffertium.  Then there were fingernet caddisfly larvae and a couple of small minnow mayflies: the Acentrella nadineae are still hanging around.

I did find a fairly mature spiny crawler nymph, genus Serratella.  Note the rich colors and patterns, and compare this to the photo I posted of the Serratella I found in the Rivanna river on 7/19.   Remember that this is usually the only genus of spiny crawler that we find in the summer.

I also found some brushlegged mayflies, and they were also pretty mature.  They were crawling around in the leaf packs along with the stoneflies.  This is the habitat they seem to prefer.

One final photo -- and this is NOT an aquatic insect!  This scary critter was on my windshield when I got back to my car.  Surely there's some naturalist out there who can tell me what this is.  I've never seen one before -- nor do I care if I ever see one again!