Flatheaded Mayflies (family Heptageniidae): Live Photos

The most popular entry I've posted, in terms of the number of "page views," is my introductory overview of the family of "flatheaded mayflies" (1/8/11).   My goal this year -- and I think I've said this before -- is to get "good," live shots of every genus I find in every mayfly, caddisfly, and stonefly family.  Since I've now got pretty good photos of 5 of the 6 flatheaded genera we find in this part of Virginia, I thought I might bring them together all in one place so monitors can contrast and compare.  What these nymphs share in common is the "flat head" (!) and eyes that are completely dorsal (completely on top of the head).  Here we go.

1) Above: genus Maccaffertium (formerly Stenonema).  Nymphs in this genus can be very big: this one was close to an inch long, not counting the tails.  Photo taken on March 28 at Powells Creek.  This is the most common genus we find, and we find it all year long.  Genus TV: range by species, 0.3 -- 5.8.

2) Maccaffertium and Stenacron found together.  Note the "streamlined" shape of the Stenacron nymph.
Photo taken on March 18 at Whippoorwill Branch.  Stenacron is not a common genus in area streams.

3) Stenacron alone.  Photo taken same place and time as above.  Genus TV: range by species, 1.7 -- 7.1

4) Epeorus.  Note the fan-like, suction cup gills.  Not common in our streams, only found in the best, and normally seen only in winter.  Photo taken on February 20 at the Doyles River.  Genus TV: 1.2.

5) A second Epeorus -- this one mature and close to hatching.  Photo taken on March 24 at the Rapidan River.

6) Rhithrogena.  Gills are similar to those of Epeorus, but they form a complete oval on the ventral side of the nymph, and it has three tails instead of just two.   I think we start to see them in April, but I've only seen them in one stream to date.  This genus, too, prefers fast, clean water.  Photo taken on April 25 at Buck Mt. Creek.  Genus TV: 0.4.

7) Leucrocuta.  The nymphs in this genus are very, very small, and very, very fast on the rocks.  They are difficult to pick up without tearing off a leg or a tail.  I associate them with good water, good streams.  Photo taken on March 24 at an unnamed tributary to the Moormans.  Genus TV: 0.

8) Heptagenia.  I have not yet seen this genus this year.  I think it's a genus we only see in the summer and only in a few of our streams.  That's a thesis I may have to revise.  Until I find a live one to photograph, here's my preserved sample from last summer.  Genus TV: 2.8. 

Exciting Discoveries at Buck Mt. Creek

Let's begin here.  This is a Spiny Crawler mayfly (family: Ephemerellidae).

And "this" is a Spiny Crawler mayfly (family: Ephemerellidae).  They don't look a whole lot alike.  But the difference is a matter of genus.  The first one is genus Drunella; the second is genus Ephemerella.  I found both nymphs today -- they were on the same rock in Buck Mt. Creek.  Ephemerella spiny crawlers are common and prolific right now in our streams; Drunella spiny crawlers -- around here -- are rare.   I have seen the genus Drunella in only four of our streams: Buck Mt. Creek, the Lynch River, the Moormans River, and Cunningham Creek (in Fluvanna County).   The genus Drunella is less tolerant of stream impairment than the genus Ephemerella.   In the "Regional Tolerance Values" for the Southeast (NC), there are seven Drunella species: they range in TV from 0 to 1.3.  The same chart has seven species of Ephemerella spiny crawlers: the range there is from 0 to 4.

While many stream monitors can recognize Ephemerella nymphs as "spiny crawlers," very few know what to do with Drunella.  Because of its "squat" shape and "muscular" forearms, it is often mistakenly listed as a flathead.    This is why it's always important to look for the gills with a loupe: do they stick out to the sides of the abdomen (flatheaded mayfly)? or are they on top of the abdomen (spiny crawler mayfly)?  Here's another look at our nymph in which the gill location is pretty clear.

Drunella spiny crawlers and Ephemerella spiny crawlers both have "Lamellate gills present on abdominal segments 3-7" (Peckarsky, et.al., Freshwater Macroinvertebrates, p. 26), even though the gill on segment 6 often covers the gill on segment 7.  The defining features for the genus Drunella are the "prominent tubercles or spines present on forefemora" (Peckarsky, ibid.).  If you click on the photos above and look closely, the tubercles are easy to see.  Here's a microscope photo to help even more.

I knew there were Drunella spinys in Buck Mt. Creek: it's the main reason I went there today, so I was not disappointed.  However, I came away with two other treasures: both caught me by surprise.
First, I saw a number of these.

This is a flatheaded mayfly, genus Rhithrogena.   This is the only stream in which I've found this particular genus (I found some here last year as well).   This genus is similar to Epeorus in having large, "suction cup" gills that seem to encircle the abdominal segments (click on the photo to enlarge).  The two differ in that Epeorus nymphs have only two tails -- Rhithrogena have three -- and the gills on Rhithrogena form a complete oval on the ventral side of the nymph.  (I regret that I did not bring this bug home with me so I could show you a microscope view of that shape: next time.)  The other thing that I think is distinctive about Rhithrogena flatheaded mayflies is the color: very yellow.  I'll keep an eye on that feature in future trips to this stream -- but it was certainly true of every nymph that I saw today.  Neat!

My third surprise eluded me until I came home and looked at what I had preserved.  I thought I had found a small minnow mayfly -- and sure enough I had.  But, whereas all the small minnows that I found through the winter -- in this stream, and every other stream for that matter -- were genus Baetis, this was genus Heterocloeon.  Here's a look at the specimen (I'll get some live shots when they get bigger.)

Like the Baetis small minnows we saw in the winter, this genus has only two tails.  The distinguishing feature is found in the gills, where "the center region" has "a large pigmented area" (Peckarsky, et.al., Freshwater Macroinvertebrates, p. 33).   This microscope close-up should help us to see that characteristic.

What else did I find?  There were still a few black flies around, and they are still genus Prosimulium (elsewhere, I'm now finding Simulium larvae).  And I found several Perlodid stoneflies, both Diploperla and Isoperla.  Looking at photos of them is a nice way to close.

Diploperla Perlodid

Isoperla Perlodid

Thank You

I want to thank all of you for your continued support of this blog.  It is very heartening to know there are so many people, both here in the states and abroad, that find these insects as beautiful and as fascinating as I do.

I hope to continue this work until the end of the calendar year -- i.e. to go through an entire annual cycle in the macroinvertebrate world.  I hope you'll continue to follow along as things unfold.

Cheers,

Bob Henricks

The Nemourid genera: Nemoura and Amphinemura

We have at least two genera of Nemourid stoneflies in our area streams: Nemoura and Amphinemura.
I've reported on both in previous entries (see the entries on 1/30, 2/24, 3/2, 3/10, 3/28, and 4/19).  Still, I thought it might be worthwhile to sum up what we know.

The photo above is genus Amphinemura, taken this morning (4/24) at Mechunk Creek: the photo below is genus Nemoura, taken on 3/1 at Buck Mt. Creek.

First, let's note similar and different physical features.  One: the nymphs of both genera are basically brown, though I would argue that Nemoura nymphs are a darker brown than the Amphinemura.  Two: in both genera the corners of the upper edge of the primary wing pads are squared off in appearance (in this they differ from large winter stoneflies).  Three: in both cases, there is a light colored stripe that runs from the head to the end of the wing pads, and on the head, this stripe takes the shape of a "T".  Four: the head in both nymphs has a triangular shape.  And five: with the tarsal segments on the legs of both genera, segment 1 is longer than segment 2 (remember that this helps us distinguish Nemourids from large winter stoneflies.)  This can be seen in the photo below.

How do they differ, anatomically speaking?  The obvious difference is that Amphinemura nymphs have cervical gills (frilly gills sticking out from the neck); Nemoura nymphs do not.  The Amphinemura gills are pointed out in the picture below.

But there is a second distinction to make -- one that can also be seen with the naked eye.  The pronotums are not shaped the same.  The pronotum on Amphinemura is large and squared off; on Nemoura it's not as big and it's more rounded.  Note the photo of the Nemoura pronotum below.

There are two other matters that are important for us to discuss.  The first is that the two genera are not  -- I think -- in our streams at the same time (at least that's what I would conclude from the work that I've done).  My first sighting of a Nemoura Nemourid was on 2/20 at Elk Run, a small tributary to Buck Mt. Creek;  my last sighting was on 3/4 at a small tributary of the Moormans River.  All nymphs that I saw seemed to be fully mature.  I did not see an Amphinemura Nemourid until 3/28 at Powells Creek, and it was very, very small.  The first time I saw one with its well-defined shape was on 4/19 at Long Island Creek.  So, my impression is that Nemoura Nemourids are around in the winter; Amphinemura Nemourids are around in the spring.

Finally, I'm not sure that these nymphs inhabit the same kinds of streams: they may have different habitats that they prefer, and Nemoura nymphs may be less tolerant of stream impairment than Amphinemura (though I have found both genera in Buck Mt. Creek).   In the winter, I found Nemouras in Elk Run, the Rapidan River, the Moormans River and one of its tribs, and Buck Mt. Creek.  If we look at the data from StreamWatch, Amphinemura Nemourids are really prolific in Fluvanna County (i.e. further away from the mountains).  (Note: StreamWatch does not ID to the level of genus, but I know from working with them that in their files, "Nemourid" means "Amphinemura".)  Major Amphinemura streams include: Cunningham Creek, the Fluvanna County reference site, Long Island Creek, Mechunk Creek, and Raccoon Creek.  However, let me quickly note that I have found Amphinemuras in Powells Creek (near Crozet) and the Doyles River -- both of which are close to the Blue Ridge.

I hope these observations will encourage more study of this very interesting stonefly.   Clearly, my thoughts on where and when we see these genera are not based on a thorough investigation.
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3/31/12: Note.  The Nemourids I found in the winter were actually genus Prostoia -- not Nemoura.  See the entry for 1/17/12.

Additional Notes on Black Fly Genera and the Case-maker Pycnopsyche

It's another dark, dreary day here in Virginia -- a good day for doing some microscope work!  So I thought I'd do some diagnostics on some of the insects I found yesterday.

First -- I mentioned in an "addendum" to my post yesterday that I had found a couple of black flies, and that they were two different genera: Prosimulium and Simulium.  This is the first time this has happened to me -- I've always found the same genus on the same day.  Since my finding so far has been that black fly larvae here in the winter are Prosimulium in genus and that they change over to the more tolerant Simulium genus in spring, I think what I saw yesterday was a stream in transition.  Let me be clear that this is an hypothesis -- not a proven fact.

How do we tell these genera apart?  Let me read from Barbara Peckarsky (Freshwater Macroinvertebrates of Northeastern North America, pp. 204-207) on the two key features that we have to find.  The first has to do with how far the "postocciput"(bottom of the head) extends around the back of the head.  Prosimulium: "Postocciput nearly complete dorsally and enclosing cervical sclerites."  Simulium: "Postocciput with a distinct and usually wide gap dorsally, not enclosing cervical sclerites."
I would conclude that the larva on the left in the photo above (I encourage you, as always, to click on the photo to enlarge it)  is Prosimulium while the one on the right is Simulium.  I have to admit that the postocciput on the Prosimulium larva does not seem to completely "enclose the cervical sclerites" -- but I think it's close enough.  The gap between the postocciput edges is very small (vs. the one on the right).

The second critical feature -- the color of the antennae.  Prosimulium: "basal 2 segments of antennae pale, strongly contrasting with darkly pigmented distal segments."  Simulium:  "basal 2 segments of antennae at least partially pigmented yellow to brown, not strongly contrasting with distal segments."
The photo below gives us a pretty good look at the antennae: Prosimulium is bottom left; Simulium, top right.  (Please click to enlarge.)

The other diagnostic photos I'm posting today are to show how we know that the "Northern Case-maker" (Limnephilid) caddis that I found yesterday is genus Pycnopsyche.  Here is a photo again of that larva.

And here is a look at another Pycnopsyche -- still in its three-sided leaf case -- that I found in this stream the last time I was here.

Again, let me read from Peckarsky on the key traits of the Limnephilid, Pycnopsyche.  "1) Head pale with dark scars and blotches; a small sclerite at posterior of each lateral hump; case of vegetable matter or sand."  And 2) "Metanotal SA1 sclerites not fused medially, although may be close together or joined by a suture."  We already have the case of "vegetable matter": here are photos of the rest of the features that we need to see.

1) Head -- light colored with dark scars/blotches

2) Sclerite (yellow patch) to the rear of the lateral hump

and 3) Metanotal sclerites not fused (the metanotum is the third segment back from the head)

Clearly not fused: genus Pycnopsyche.  What a nice way to spend a crappy spring day!

After the Flood: A Look at My Trib to the Moomans

                                      Just look at the ugly places I have to go to find insects (!)

The storm over the weekend dumped, I've been told, 5 inches of rain into the Moormans in Sugar Hollow.  The river flooded all three bridges that cross over the river as it makes its way down the valley.
So I didn't know what I might find today in my "hidden stream" (see previous entries) that steeply descends into the river below.

The water, even in this little stream, was still fast and high: still, I had no trouble finding insects -- this is very fertile water.  But I do think the flooding impacted what I was able to find.  To wit -- I did not find a whole lot of stoneflies: one Perlid (common stonefly) , two Perlodids, and two Peltoperlids (Roach-like stones).  All of these were in leaf packs, but that's not many nymphs given the number of leaf packs that I sorted through.  I suspect that, since leaf packs were clearly flushed from one place to another by the flow of the water, they have not yet been re-populated.  But there may be other ways to explain this.
Anyway, some photos.

1) Peltoperlid (This was a big one, close to 3/4" long.)

2) Perlodid (Isoperla similis)

You may notice that its left eye is missing!  I don't think I did this with my tweezers; I never pick up bugs by the head.  I guess that bad things can happen in nature.  Was it an accident?  Or did he run into a bigger stonefly?!

I actually found more insects on the rocks than I did in the leaf packs -- and that's rare.  Some rocks were covered with flatheaded mayflies, mostly genus Epeorus, but also a fair number of Leucrocutas and a few Maccaffertiums.   Down in the valleys, a lot of the Epeorus flatheads have already hatched: at this high elevation, there are some that are close to hatching -- but many that still need to grow.  Here's one in the pre-hatch stage with very dark wing pads.

I saw a few Ameletid mayflies -- but they're getting scarce.  Also on rocks, a lot of Uenoid case-maker caddisflies -- which surprised me.  In other streams that I visit, Uenoids are mostly now in pupation.  Again, that that is not yet occurring up here is probably due to elevation.  One of the Uenoids I found had a very nice case.  My photo's not great, but it will do.  The large stone chips on the sides of the case are characteristic of Uenoid construction.

And I found another "Northern Case-maker" (Limnephilidae) here, genus Pycnopsyche, the very same type of larva I found here last time.  I waited a long time for this bug to emerge from its case (the three-sided case made of leaf fragments), but it just wouldn't come out, even when a flathead sat on top of the case and a netspinner (genus Diplectrona) came by for a visit!

So I gave him a sip of alcohol from one of my vials, and he finally made an appearance.  In this photo, the "lateral humps" on the first abdominal segment that are characteristic of this caddisfly family are easy to see.  Remember they're used to stabalize the larva inside its case so it can move its abdomen up and down, generating a flow of water (for oxygen).

Finally, I also found some "Net-winged midges" on rocks.  This is the midge (Blephariceridae) that's very intolerant of stream impairment.  I took two photos, getting dorsal and ventral views.  You may recall that on the ventral side, this midge has little "suckers" that help it hold on to the rocks.   But there are also "gill tufts" on the segmented body -- something I've not seen before.  They're very clear in Voshell's illustration (J. Reese Voshell, Jr., A Guide to Common Freshwater Invertgebrates of North America, p. 171).

Dorsal

Ventral

Addendum:  There were also quite a few spiny crawlers here -- but nothing like I've been seeing in other streams.  And, I picked up a couple of black flies: one was Prosimulium, the other was Simulium!

Stream Report: Long Island Creek -- Important Revisions!!!

Having looked through my microscope at the insects I brought home from Long Island Creek, I find that I have some revisions and additions to make to the entry I posted this morning.

First, the picture above does not represent a revision so much as an addendum: this is a microscope photo of the Nemourid stonefly for which live photos were previously posted.  In this, the image is sharper, so the Nemourid features noted this morning can be more readily seen.  (But his one tail is still missing!)

Second, I mentioned that I had found some black fly larvae.  When I looked at them under the scope I realized that they were genus Simulium, not genus Prosimulium, the genus I've been finding all winter.
My feeling last year was that there was a changeover from Prosimulium to Simulium larvae sometime in April, and this provides more evidence for making that point.  Remember that Prosimulium black flies have a tolerance value of 2-3: Simulium, in most lists, are given a value of 6.   But, it is apparently the Prosimulium black flies that amass the huge "colonies" we see in the winter: Simulium black flies seem to stick to rocks in smaller clusters.  (John Murphy suggested this to me, and I intend to pay careful attention to this through the spring.)

Two features distinguish Simulium larvae from Prosimulium: 1) Simulium antennae are clear; Prosimulium antennae have a black tip (this was mentioned in a previous entry): and 2) on Simulium larvae the "postocciput" (the back edge of the head) is incomplete, leaving a big gap at the base of the head.  We can document those features in the larvae that I found this morning.

1) antennae

2) postocciput and gap

The third thing I discovered when I looked at the bugs through my scope? -- what I had called a "trumpetnet" caddisfly (Polycentropodidae) was not: it was a fingernet caddisfly, and I think it's genus Wormaldia.  That would make it a first for me.  This is one of three fingernet genera, the other two being Chimarra (our most common), and Dolophilodes.  Of the three, Wormaldia is the least tolerant of stream impairment with a TV, in some lists at least, of .4 (Chimarra is 2.8; Dolophilodes is 1).  So, "if" I'm right -- and that's a big "if" -- this would be very exciting.  Here's a picture of the larva in question, then we'll look for the features we need to find for confirmation.

Wiggins  -- Larvae of the North American Caddisfly Genera (Trichoptera), p. 316 -- notes three features that distinguish the Wormaldia genus.  1) "The anterior margin of the frontoclypeal apotome is symmetrical."  That is, the front edge of the head is symmetrical.  Frankly, I can't really be sure of that from what I can see with my scope, but I think that it is: the piece sticking out from the head in the picture below is part of the mandible.

2) "The fore trochantin projects freely as a small, knob-like process," and 3) "On the ventral surface of the head, seta (hair) no. 18 is ... stouter than any of the dorsal head setae."  Those features I think can be seen in the following photo.  (Please click on the photo to enlarge the image.)

I invite other opinions.  If there are experts out there who feel I am mistakenly reading the data, I am happy to be corrected.  Until then, I think that this is a Wormaldia fingernet caddis.

Stream Report: Long Island Creek -- Nemourids and Spiny Crawlers

Let's start with the "prettiest" insect I found this morning: this Perlodid stonefly, genus Isoperla.  The dark wing pads are a sure sign that it's getting ready to hatch, so it's much further along than the Isoperlas I've been finding in other streams.  (Is that because I was in Fluvanna county, further away from the mountains?)  Still, I must apologize for this and all of my photos today: I had very poor light conditions, so none of my photos is as "sharp" as I'd like it to be.  One other shot of this Perlodid.  (All of the photos look a little bit better if you click on them to enlarge them.

In addition to this lonely Perlodid, I found a number of Eccoptura common stoneflies (Perlids), one Leuctridae (Rolled-winged stonefly -- very small), a couple of flatheaded mayflies (genus Maccaffertium), a few Uenoid case-maker caddisflies (not yet pupating here), some netspinners (genus Diplectrona -- the "intolerant" one), one freeliving caddisfly (gray body), and one "trumpetnet" caddisfly.  (Oh, yes: and some hellgrammites, black flies, and crane fly larvae.)

But the dominant taxa were Nemourid stoneflies (genus Amphinemura), and spiny crawlers -- the insects that tend to take over our streams in the spring.  I picked up a lot of Nemourids.  They were still on the small side, but for the first time this year I saw a Nemourid that I could tell by its overall shape was a Nemourid.  Here's the best picture I managed (and I'm sorry that I apparently broke off one of its tails!)

Note the triangular shape of the head; the large, square-shaped pronotum; the square shape of the top of the primary wingpads; and the sloping shape to the wing pads as a whole -- they kind of curve in then flare back out to the tips at the end.  Also characteristic -- the light line that runs from the head to the ends of the wing pads, and the "T" shape of that line on the head.  And, note the color: uniformly dark brown.

If you see enough of these in the spring, you can pick them out in your tray by picking up on these traits.  Of course the other feature to look for -- the "cervical" gills that stick out from both sides of the neck.  No matter how small your nymph might be, the gills can almost always be seen by using a loupe --sometimes with the naked eye.  Look at the size of the gills on this tiny nymph.  (Please click on the photo to enlarge it.)

Almost all of the Nemourids I found were crawling on the bottoms of rocks; a few were in leaf packs.
All of the spiny crawlers were, again, picking their way through the moss on the rocks that were covered with water.  These are the taxa -- Nemourid stones (genus Amphinemura) and spiny crawler mayflies (genus Ephemerella)-- that will dominate samples in a lot of our streams throughout April and May.  (Below, Long Island Creek in the spring.)

Maturation of "Diploperla" Perlodid stonefly nymphs

Since we appear to be reaching the point at which Diploperla (genus) Perlodid stoneflies are going to hatch, I thought I might do another "review of the growth stages" we can perceive if we follow them over a number of months.  In the previous entries I've done of this sort (for small minnow mayflies, large winter stoneflies, etc.), I've stressed 1) changes in color (they get darker), 2) changes in the richness of detail in patterns, and 3) how the wing pads get longer.  Here, the color and pattern changes are not as pronounced, but the wing pads clearly lengthen and change in shape as the nymphs mature.

But let me begin with a review of the anatomical features that help us ID this particular genus.  There are two features that prove to be key.  They are -- and I'm quoting Peckarsky, et.al., Freshwater Macroinvertebrates of Northeastern North America -- 1) "Posterior ends of arms of mesosternal ridge meet posterior edge of mesosternum separately," and 2) terminal lacinial spine long, 1/2 as long as lacinia."  Here's a microscope shot of the Diploperla mesosternum showing the "arms" and the "posterior edge" of the mesosternum.

Clearly, the arms meet separately.   This contrasts sharply with what we see when we look at the mesosternal ridge of the Perlodid genera Clioperla and Isoperla where the arms form a "Y".

Next, we look at the lacinia, and the lacinial spines of the Diploperla stonefly.  We are looking at the underside of the head.

Note the length of the terminal lacinial spine in relation to the length of the lacinia as a whole.  Also note that there are no "hairs" or "spinules" below the second lacinial spine -- as we would find with most other Perlodid nymphs.

On to our photos that show the Diploperla nymphs developing over time.  The first photo I have in my collection comes from February.  But I'm quite sure I started to see this genus in January -- at that time, they were too small to photograph at the stream.

2/13: Powells Creek.  Note that the colors are much the same as they will be when the nymph is fully mature, but, look at the wing pads -- the posterior edges are almost straight across (i.e. not at all curved).

3/18. Whippoorwill Branch of the Mechum.   This is not quite as dark as the mature nymph will be, but note the slight curve in the back edges of the wing pads.

4/11: Doyles River.  This nymph is much darker in color, and the wing pads are longer and even more curved.

4/18: Powells Creek.  Finally, the fully mature nymph -- one that's ready to hatch.  Note the length and shape of the wing pads.  And note that the primary and secondary wing pads are shaped differently on Perlodid stoneflies.  The back edge of the primary wings forms an arch; the arms of the back edge of the secondary wings meet at an angle.  And the colors and patterns are very rich.  What a beautiful insect!

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(The following Diploperla nymph -- even closer to hatching than the one pictured above -- was found on 5/14 at the Lynch River.  For more photos, see the entry for 5/15.)