Friday, September 30, 2011

Is the Acentrella Turbida Small Minnow Mayfly a "Bi-brooded" Species?

(If you have not already done so, be sure to read the previous entry -- "Acentrella Turbida: Our Fall Small Minnow Mayfly") before reading this one.)

The picture above was not taken this morning: it was taken on May 9th at the Rapidan River.  (Double click on the photo to have a clear view of the "long, dense setae".)

In the entry I posted this morning,  I mentioned in passing that I wasn't entirely sure that some of the small minnow mayflies I found at the end of the spring/start of the summer were not A. turbida nymphs -- the nymph that I expect to see in the fall.  Let me show you additional photos -- in addition to the one at the top of the page -- of the nymphs that I had in mind.

5/9, Rapidan River

5/9, Rapidan River

6/6 Rapidan River

6/24, Moormans River

6/24, Moormans River

Note that the nymph found on 6/24 is fully mature and ready to hatch.   Now, I know there is an A. turbida hatch in the Moormans late in the year: I found a lot of A. turbida nymphs in the Moormans last year at the end of October.  So, if the nymph in the photo above is A. turbida, there are clearly at least two generations of this particular species in at least one of our streams.

The similarity between the nymphs you see on this page and those in the previous entry, the nymphs that I found this morning, is striking.  Both have the broad thorax typical of A. turbida nymphs, and of course, both have only two tails.   Unfortunately, I did not preserve any of the nymphs pictured above, so I cannot be sure that they were A. turbida nymphs.  I know at least some of them were Acentrella -- no visible rear wing pads.  But I know I did not look for the long, dense setae on their legs: I did not expect to see A. turbida nymphs in May and June!

Knopp and Cormier -- Mayflies: An Angler's Study of Trout Water Ephemeroptera, pp. 63-64 -- put Acentrella turbida into a group about which they say, "Nymphs of this complex are generally bi-brooded, usually producing concentrated hatches in June-July and again during September-October, with occasional sporadic hatches in between."  And they add, "...under ideal water and phototropic conditions, the eastern hatches of Acentrella turbida may produce three broods with peak hatches timed to May, August, and October."

Well, well.  I've been hoping to see a "second generation" of at least one small minnow species, and maybe we've got one.  Clearly, in October and early November, I'll be looking for A. turbida nymphs in the Moormans and Rapidan Rivers.  But I'll also have to document the small minnow mayflies I find next year with greater care.

Another one: 6/15, Moormans River in Sugar Hollow

Acentrella turbida: Our "Fall" Small Minnow Mayfly

This is another "Fall" insect I was hoping to find, and sure enough there they were in the Lynch River this morning.  Small minnow mayfly (Baetidae) -- Acentrella turbida.   I have only seen this small minnow species in three of our streams -- the Lynch River, the Doyles River, and the Moormans -- and I've only seen it in the fall.  While I can't say for sure that they aren't around any other time of the year (I'm suspicious of a couple of nymphs I found in early summer in the Rapidan and the Moormans), when I want to see them, I look in September, October, and early November.  Of the nymphs that I found this morning, one was already mature -- dark in color with long, black wing pads.

How do we know these small minnow nymphs were Acentrella turbida in terms of genus and species?
Well, they have only two tails, so they're either Acentrella or Heterocloeon in terms of the genus.  But, most species of Heterocloeon have visible rear wing pads and forecoxal gills.  These nymphs do not have forecoxal gills, and hind wing pads are absent.

There is one species of Heterocloeon (Heterocloeon amplum) that does not have the forecoxal gills and hind wing pads -- but it's a fairly large nymph, 7-9mm.  The two nymphs pictured above were 4mm and 5mm, exactly what they should be if they're A. turbida nymphs.

We have Acentrella.  And now for the species.  A. turbida nymphs have two distinct features: 1) the thorax is broad, wide.  Clearly the case with these nymphs.  When you see them swimming around in a tray, they lack the "streamlined" look we expect to see with a small minnow mayfly.  They can be, and have been, confused with flatheaded mayflies.  2) The other feature requires a microscope photo.  The leg segments -- femora, tibiae, and tarsi -- are covered with long dense setae (hairs).  Have a look.

This dense setae also shows up in a photo I took in late October last year.  (Note the very broad thorax.)

So there we have it: Acentrella turbida.  I'll turn my attention to finding some small square-gill mayflies (Caenidae) and one or two "rolled-winged" stoneflies (Leuctridae) which are also around in the Fall.

Some more views of the A. turbida nymphs from today.

Oh.  The tolerance value of A. turbida is 2.0 (NCDWQ): look for them in "quality" streams.

Thursday, September 29, 2011

Back to the Streams: the Doyles and the Moormans

Hallelujah!  The sun actually shined today in central Virginia: there is hope.  I should have been mowing my lawn -- but who could resist seeing what's going on in the streams.  So I went off to the Doyles River to the north of White Hall and then up to the Moormans in Sugar Hollow.

In the Doyles, the dominant taxon was the common stonefly (Perlidae).  The leaf packs were literally crawling with them -- I didn't see a single insect on the bottoms of rocks.

Now, at this point in the game, I hate to say that I'm stymied, in terms of genus and species, by a couple of common stoneflies -- but I am.   I must have seen 20-30 Perlids in the leaf packs at the Doyles -- most of them, I think, genus Acroneuria (the characteristic brown color with the yellow "M" on the head) -- but I only photographed and preserved the two in the picture above.  They had unusual colors.  Let's take a closer look.

1) I think this might be an immature Acroneuria carolinensis:

This keys out as genus Acroneuria -- there are not "spinules" on the occipital ridge, and there is clearly a "fringe" of silky setae at the base of the cercal segments.

And, since the abdominal segments are "light" at the top and dark at the bottom, I'd move towards A. carolinensis.  Still, I'm bothered by two things that don't seem to fit: 1) the "M" on the head, doesn't look like the "M" that we normally see -- the sides are too rectangular, and the entire thing should be anterior to the median ocellus, here it encloses the median ocellus. (???)

2) I'm also bothered by the overall color -- it's too yellow.  But, that might be because it's immature; it may darken as it ages.

2) The second nymph might be genus Beloneuria:

Beloneuria nymphs key out the same as Acroneuria nymphs -- with one exception: Acroneuria nymphs have a fringe of silky setae on the basal cercal segments; Beloneuria nymphs do not.   This nymph has subanal gills (Acroneuria nymphs rarely do) and whorls of spines on the cercal segments -- but no silky fringe.

So, what's my hesitation in declaring this Beloneuria?  Well, I've never seen this genus before, and Stewart and Stark (Nymphs of North American Stonefly Genera, p. 326) do not list Virginia as a state where the presence of this genus has been attested.

So, for the moment I'm stymied.  If I resolve my doubts, I'll let you know.  The other things of interest I found in the Doyles were a couple of "tiny" crane fly larvae.  At this stage in the game -- the autumn -- these larvae are not the fat, gray, chubbys, that stream monitors commonly see.  Have a look.

This larva was about 5-7mm long and 2-3mm wide.  Still, the main features we look for on this type of larva are already easy to see.  There are well-defined "welts" on the abdomen, and we can also see the unique "spiracular plate" at the tail end.


Off to the Moormans.  The dominant taxon here was the small minnow mayfly, though I also saw some netspinners and fingernet caddisflies, a few small flatheaded mayflies, snails (Pleurocerids, Physids, and Planorbids), and a few common stoneflies (genus Acroneuria).  The small minnows were the same two species that I've been seeing here for the last couple of months -- Baetis intercalaris and Acentrella nadineae.  I got a good "double" on two of the B. intercalaris nymphs.

The surprise of the day was this "Water Scavenger Beetle" (Hydrophilidae).

Another look:

We really don't see them that often, and I'd expect them in the Rivanna -- not in the Moormans!  This beetle is predaceous -- so handle with care!

Back to "work" tomorrow -- I think I'll go up to the Lynch.  But I have to leave time for mowing the lawn!

Sunday, September 25, 2011

The "Case-makers": An Annual Wrap-up

I've found some beautiful case-maker caddis this year, and it's a good time to review what we have seen, when we have seen them, and where.  I'll pretty much move through these in chronological order.

1. Uenoidae, common name "Uenoid".  Genus Neophylax.
The caddisfly in the picture at the top of the page is a "Uenoid" caddis, found on February 18th in Elk Run, a tributary of Buck Mt. Creek.  I started finding Uenoids on December 11th and continued to find them through April (even May, I think, in some small, mountain streams).  I think of the Uenoid as a "winter" case-maker since that's normally when we find them, and in some streams they are numerous and cover the rocks.   We find them in streams of all sizes -- though I've never seen them in "big" rivers like the Rivanna.  The cases are tube-like, usually slightly tapered, and normally have three large pebbles on each side, perhaps used for ballast -- though agreement on that is not universal.  Another photo below, pointing out the large pebbles on the sides.

2. Glossosomatidae, common name "Saddle case-maker."  Genus Glossosoma.
This is not a real case-maker according to Wiggins (see his Caddisflies: The Underwater Architects, pp. 20-28).   Unlike true case-makers it does not, for example, keep the same case throughout its life as a larva.  When it gets too big for its case, it abandons the case and makes a new one that's more "fitting" (Sorry. Couldn't resist!)  This is another caddisfly that I think of as a "winter" case-maker.  Again, I saw some on 12/11/10.  I found them on occasion through the winter months, but I also found some in June -- and even in August!  Still, we're most likely to see them in the winter months -- December through March.  The "saddle" case resembles the shell of a tortoise.  Normally, you won't see the larva until you turn the "shell" over (though sometimes they "peek" out from underneath, as in the first photo below).  Below, photos of the dorsal and ventral views, then one with the larva crawling out of its overturned shell.

3. Lepidostomatidae, common name "Lepidostomatid".  Genus Lepidostoma
Another "winter" case making caddis -- though in one small tributary to the Moormans, I did find one in June.  Most of the Lepidos I found, I found in January, February and March.  They commonly make a case that is 4-sided, skillfully crafted out of square pieces of bark.  Some of these are gorgeous when seen with magnification.  This, too, is primarily a small stream insect: look for them in forested, headwaters streams.  But, for whatever reason, we have found them in the Rivanna at Milton.  Below, three examples.

4. Brachycentridae, common name "humpless case-maker".  Genus Brachycentrus.
I'm not sure how to give these a date.  Ames (Caddisflies, p. 175) identifies this -- in fly fishing terms -- as the "American Grannom," and gives hatch dates from March through May.  But I've found these in the fall, winter, spring, and summer in the Rapidan River.  I've found them here and there in a lot of the streams I explore, but I've only seen them in large numbers in the Rapidan River.  Cases vary by genus.  But Brachycentrus is the genus we most commonly find, and their cases are 4-sided, put together in "log cabin" fashion, out of ribbons of bark -- miracles of case composition.  Two examples below, both from the Rapidan River.

5. Limnephilidae, common name "Norther case-maker."  Those pictured below are genus Pycnopsyche.
This is the largest case-maker we normally see (I did not see any "Giant" case-makers (Phryganeidae) this year, though we have found a few in the past in some of our streams.)  The Limnephilid is a "spring" case maker.  I found them this year from the end of March through the beginning of June.  And, they prefer small streams -- really small.   They make a variety of cases which tend to be "genus specific."  But all of the Limnephilids I found keyed out as Pycnopsyche.  Photos below, beginning with my favorite case -- the three-sided case made of precisely cut pieces of leaves.

Other Limenphilid cases (the larvae were hidden inside):

6. Leptoceridae, common name "Long-horned case-maker".  Genus Nectopsyche.
I think of this as a "summer" case-maker, and one that we primarily find in big rivers, i.e. the Rivanna, main stem.  I've found them in other streams -- never small, mountain streams -- but when I want to look for them I head to the Rivanna, and the Rivanna at the bridges at Milton and Crofton.  They get their common name from the fact that they have long, visible, antennae both as larvae and as adults.  The genus Nectopsyche -- the one we commonly see in the Rivanna -- attaches its case to the sides of stems of vegetation.  The cases are very hard to see if you're out, like me, lifting up rocks.  These photos -- not the best -- were taken in June.

7. Odontoceridae, common name "Strong case-makers."  Genus Psilotreta.
This is a case-maker we can find, in theory, just about any time of the year since it has a two-year life cycle.  But, they crawl around on rocks, only in "fall," and that's when we normally see them.   I look for them in September and October.  The cases are very strong and cannot be easily broken.  I've only seen them in two of our streams: the North Fork of the Moormans and the Rapidan River.  This is a very intolerant family, so you'd better look for them in clean, cold, mountain streams.   The photos taken below date from 9/17.

Detailed discussions of all case-maker families were posted in earlier entries.

Friday, September 23, 2011

The Perlids (Common Stoneflies) in Our Streams

We've had clouds and rain all week -- with more rain on the way.  Ugh!  While I wait for the clouds to clear so I can get back to the streams, here's a quick look at the members of the "Common" stonefly family that, to date, I've found in local streams.  I'll note them by genus -- including the name of the species where I know it.

1.  Acroneuria abnormis -- pictured above.  This is the most common stonefly we see in our streams.

2. Acroneuria carolinensis.  To date, I have only found this species in the Rapidan River.  Abnormis and carolinensis differ primarily in the nature of the banding on the abdominal segments.

3. Agnetina.  I have only seen this genus in the Rivanna River.  Pictured is a small, immature nymph.  If I can find a larger one this fall, I will try to determine the species.

4. Paragnetina immarginata.  I have only seen this genus in the Rapidan River.

5. Neoperla.  I have only seen Neoperla in Powells Creek in Crozet.  Differs from all other "Commons" in having only two ocelli (not three).

6. Perlesta.  Fairly common, and found in both small streams and large rivers.  This seems to be the last Perlid to mature and hatch in the summer.  I saw them well into July, but I didn't see any anywhere until late May.

7. Eccoptura xanthenses.  This species seems to be confined to small streams, "tiny" streams.  I've seen them in Powells Creek, the Whippoorwill branch of the Mechums, and in two of the Moormans tribs that I explore.

That's it.  Of the genera keyed out and ID'd in Peckarsky's Freshwater Macroinvertebrates of Northeastern North America (p. 69), I have not yet found: Perlinella, Hansonoperla, Beloneuria, and Attaneuria.  The search goes on.


All photos of these and other insects can be viewed at:

Open the folder "live photos only".