Searching for Small Minnow nymphs: A Look at Powells Creek

(Please note that Blogger has been down for almost 24 hours, and my post from yesterday was lost  and apparently cannot be restored.  So, I'll reconstruct it the best that I can.  My trip to the Powells was on 5/12/11.)

No.  This is not a "small minnow mayfly" (Baetidae).  But let me clean up some unfinished business before I move on to my mission.  If you've been following along in a regular way, you'll recall that I found three of these nymphs -- the one in the photo above -- at the Rapidan River last week.  This is a Perlodid stonefly, and in terms of genus, it keyed out to either Clioperla or Isoperla; I was quite sure that it was the latter.  I now have confirmation that that is correct.   Roger Rohrbeck with Bugguide.net informed me this morning (5/12/11) that this appears to be Isoperla holochlora, and told me to take a look at the photo by Donald S. Chandler at http://www.discoverlife.org/mp/20p?see=I_DSC520&res=640.   So, that mystery is solved.  I found a number of these today in Powells Creek.  (And I can add that I found a "ton" of them this morning -- 5/13/11 -- in the Doyles River at Doylesville.)

Now on to the main matter at hand.  I came to the Powells to look for small minnow mayflies since they are showing up again in Buck Mt. Creek.  I only found two -- but they're interesting samples for us to look at.

Notice that both nymphs have three tails.  Every nymph I found in the winter had just two tails.  Here's a look at a nymph from Buck Mt. Creek in the winter to jog everyone's memory.

Every nymph I found in the winter was genus Baetis.  By contrast, the "new" small minnows I found at Buck Mt. Creek were Heterocloeon (pigmented gills, but still two tails) and Acentrella (two tails, but a very broad upper thorax).

In the version of this current entry that I posted yesterday, I claimed that the two nymphs I just found in the Powells were genus Baetis -- just the form with three tails instead of two (there are two kinds).  Let me take advantage of this "re-post" to qualify the claim that I made.  I think they were both genus Baetis: I cannot really be sure.  Why?  Because I stupidly forgot to bring the second nymph pictured above home with me to my lab!  And, with the first nymph above,  I saw "metathoracic wing pads," which normally means genus Baetis, then discarded my sample, only to remember that with the "three-tailed" Baetis you need to check the shape of the labial palps to be sure of the genus ID (see Peckarsky, Freshwater Macroinvertebrates, pp. 35-36 on this point.)   So, I'll have to return to the Powells for more samples.  In any event, the critical point is that the nymphs I found in the Powells were not 1) genus Heterocloeon, 2) genus Acentrella, nor were they 3) the same type of Baetis that I found in this stream in the winter.

Why is this important -- or at least interesting?  Because small minnow mayflies can produce more than one generation a year.  The nymphs that hatch in late winter can lay their eggs, which can grow and mature through the spring and summer to hatch in late summer or fall.   Will we see a "second generation" of the bugs that we saw in the winter?  Possibly, and I'm looking.  But I don't think I've seen that so far.

Oh. One other thing on the one small minnow nymph that I found yesterday.  Unfortunately, I put it in the tray along with a Perlodid stonefly (genus Diploperla).  Big mistake.  As I looked on, the stonefly started eating the small minnow mayfly!  At first I thought -- "This will be neat -- to snap photos of the progress made by the stonefly as he devours the mayfly."  Then I remembered that I needed the mayfly for purposes of genus ID, so I quickly put a stop to the action!  (I was already too late to save the tails and the very end of the abdomen.)

Let me finish up with some nice photos I took of three other insects.

1) a Perlid stonefly (common stonefly), Eccoptura xanthenses

2) a HUGE Freeliving caddisfly larva.  This was slightly over an inch in length.

and 3) another nice Flatheaded mayfly, genus Epeorus

Another Return to Buck Mt. Creek

I found some very unusual things today at Buck Mt. Creek -- and we can begin with this really neat Rhithrogena (a genus of flatheaded mayfly).  I first reported on finding this genus at Buck Mt. Creek in my post of 5/1, noting that the color is normally yellow.  But look at this!  The head is white, as are two segments at the end of the abdomen.  I've never seen anything like it.  Is this a matter of species?  Or is it just the coloring of one individual nymph?  Questions I can't really answer.

On 4/25 I reported on another find I had made at this stream: a genus Drunella spiny crawler mayfly.
I've not seen them in a lot of our streams, and the only time I saw a good number at the same time was in a StreamWatch sample we took at the Moormans River last spring.  Sure enough, the first three insects I found on the rocks today were all Drunellas!  One was a real beauty.  (Remember that these differ from the spinys we normally see by having "muscular" fore legs with "tubercles" on them.)

A second Drunella nymph was unusually large -- but the colors were drab and it was covered with silt.  I took a few pictures of it anyway, not intending to use them.  When I looked at the photos at home I discovered that this one has a really odd looking head: the corners of the head are pointed like horns.  Take a look.

Wierd, wierd!  I'm going to send this photo to the folks at Bugguide.net to see if they know the species.

Now, for the main reason I went back to Buck Mt. Creek so early (I was just here on May 1).  In my post of May 1, I noted finding some small, small minnow mayflies of whose genus ID I was not really sure.  I was split between Baetis and Acentrella.  Did they or did they not have metathoracic wing pads (they show on Baetis nymphs but not Acentrella.)  So I was hunting today for some small minnows.  I found four, took some live pictures, and examined them closely when I got home.  Acentrella.  No sign of those wing pads at all.  And, at the stream I was already pretty sure of this call given the shape of the nymphs.  They had very "broad shoulders", i.e. the thorax is wider than anything I've seen on a Baetis.  Here's one of my shots.

This is very interesting.  In the winter, every small minnow I found in this stream was genus Baetis.  Then on 4/25, I reported on finding a Heterocloeon.  Now we have Acentrella.    Could it be that the winter small minnows are always Baetis, while in the spring we find both Heterocloeon and Acentrella replacing the Baetis?  Stay tuned.  This is a matter that I will explore as the spring and summer continue.

But I was in for yet another surprise in my visit this morning.   I picked up a stonefly that I thought was another Perlodid, probably a species of Isoperla.  But I couldn't be sure since it was small and the colors were poorly developed.  I preserved it and brought it home.  I readily saw that I was wrong.  It was a very small Perlid (common stonefly), and the genus is one that I've seen just a few times -- genus Perlesta.  Here's a live shot that I took at the stream of the nymph in question.

It's easy to see from the photo that this is a Perlid -- it has "hairy armpits" (Rose Brown's expression), frilly gills that stick out from the body behind each pair of legs.   But how do we determine the genus?
The first thing we have to look at is the back of the head.

Now, here are out options (I'll be quoting from Peckarsky, et.al., Freshwater Macroinvertebrates, p. 69):

1) Occipital ridge present; a closely set regular row of spinules completely across back of head inserted on occipital ridge...
or
2) Occipital ridge absent; spinules on back of head present mainly near eyes, or arranged in a transverse row of varying completeness, but always at least a little wavy or irregular...

I've highlighted my choice.  That eventually takes us to another couplet:

1) Branched subanal gills present; head patterned....Perlesta
or
2) Branched subanal gills absent; head monochromatic brown....Attaneuria

The head is clearly patterned, and, yes, it does have subanal gills.

It's genus Perlesta.  It's worth noting that this is the first time I've found tiny, immature Perlids since I started this project last fall.  The eggs by terrestrial Perlids last fall probably wintered over as tiny nymphs in the substrate and are just starting to grow and mature in the warmer waters of spring.  Perlids typically hatch and mate in July and August.

I took two other good photos that are worth showing in closing.  The first is a Perlodid stonefly, genus Isoperla (possibly Isoperla montana), the second is a tiny flatheaded mayfly, genus Leucrocuta.

Exploring New Waters: Finding More Treasures

Today a friend took me to yet another trib to the Moormans that, like the others I visit, stays unnamed -- it's on private land.  I collected a lot of neat bugs, got ready to take some pictures, and proceded to tip over my container!  Yuck!  But I did manage to hold on to this one (and a few others).

This is a spectacular Limnephilid -- Northern case-maker caddis -- genus Pycnopsyche.  This is the genus that often makes a three-sided case out of leaves when it's small, but it turns to other construction materials as it matures.  Here's a perfect example of that.  The back of the case is still the three-sided case made of precisely clipped sections of leaves: the front of the case is made out of pebbles.  Case-makers do not abandon their cases as they outgrow them; rather, they enlarge their cases by adding things on at the front.  Here's a good look at the case on its own.  (The case, by the way, was 1 1/2" long, and the larva was an inch long.)

A thing of beauty.  All of these building blocks are "glued" together with the silk that the larva produces inside its body; the silk is generated by special silk glands at the front of the head.    Although it's sometimes difficult to get these larvae to stick their heads out for a picture, this one almost crawled right out of its case as I was watching.

I was fairly certain of the Pycnopsyche identification.  Nonetheless I preserved this so I could check it out in my lab (and, yes, I wanted it for my reference collection!).  Pycnopsyche for sure.  The two key features again:  1) sclerites at the back edge of the lateral humps; and 2) the "SA1" metanotal sclerites are not fused.  Here are the photos for confirmation.

This stream -- like just about all of our streams at the moment -- was loaded with spiny crawlers, genus Ephemerella.  I'll spare you the photos.  But I also collected: Common stoneflies, Roach-like stoneflies (lots of them), a free-living caddisfly (creamy white color), several common netspinners (genus Diplectrona), a "small" Giant stonefly, and lots of flatheaded mayflies, genus Epeorus.   I did get a good photo of one of those.

This one still has a while to go before it thinks about hatching.  I also found several Perlodid stoneflies that I think are the same genus and species that I found at the Rapidan River on Thursday.  Here's a look.

This nymph is more mature than those that I found on Thursday (note the spread in the wing pads), and under the microscope, the brown stripes on the abdomen that are typical of Isoperlas were very clear.  So, I do indeed think we've run into yet another species of Isoperla -- I think there's a very good chance that it's Isoperla transmarina (I'll keep you informed).


As I headed back into town from Sugar Hollow, I decided to have a brief look at the Doyles River, hoping to find a new brood of small minnow mayflies.  I didn't succeed.   I did see a lot of Epeorus flatheaded mayflies and some of our new species of Isoperla.  But I also found a fair sized Polycentropodid -- a "trumpetnet" caddisfly larva.  We don't see too many of these, though I think that volunteer samplers often record them as fingernet larvae.  Here's a decent photo that I managed to take -- actually, it's the first time I've gotten a live shot of this insect.

Samplers often take one look at the burnt orange head and write this off as a fingernet.  But there's not a hint of yellow or orange in the body (as there would be were this a fingernet).    Polycentropodids are either creamy white, like this one, or a pale shade of tan.  But the key thing to note is the head.

The "freckles" that cover the head are called "muscle scars," and "muscle scars" are a distinguishing trait of this caddis family.  The other feature that helps us to make this identification requires the use of the microscope.  The "fore trochantin" -- sort of the front shoulder blade -- is pointed.  Have a look.

One final note on this insect.  The genus is Polycentropus -- the only genus I've seen around here.  How do we know?  Well, it's a case of "X marks the spot".  A Polycentropus Polycentropodid has a black X on the back of its anal proleg.

The Pronggilled Mayflies: Pictures of how they change as they mature

This nymph was among the insects I found yesterday at the Rapidan River.  It's clearly a Pronggilled mayfly (family: Leptophlebiidae; genus: Paraleptophlebia) -- the "Blue Quill" to fly fishermen.  If you click on the photo to enlarge it, the "pronged" gills are easy to see.  But this is unlike any nymph of this family that I've seen before.

Having looked at photos of adult, terrestrial pronggilleds on Troutnut.com last night (http://www.troutnut.com/specimen/683), I quickly realized that I had found a nymph that was very close to "making the change".  The head is already the head of the terrestrial form; so too is the abdomen -- with the exception of the few gills that still stick to the sides.  But, the wings have not yet fully emerged; they're still encased in the long, black wing pads of the pre-hatching nymph.  It's possible that this nymph had moved to the surface, or was on its way to the surface to fully emerge, when I picked it up.  In my tray, it stayed on top of the water -- it never went down to the bottom.

One further point: note the VERY large eyes.  This is a sure sign that this is a male.  Male mayfly adults have large eyes to help them see the females for mating as the imagoes swarm over the stream.  Another look, with a good look at those eyes.

Having reached this realization, I remembered that I had found and photographed pronggilled nymphs on my two previous trips to this river this winter.  So, let me show you the photos I took on those visits.
Once again we can see how two things occur as a mayfly nymph grows and matures: 1) the wing pads get longer and darker, and 2) the nymph gets darker in color, and any patterns show up in greater detail.

2/23: Pronggilled mayfly at the Rapidan River

3/24: Pronggilled mayfly at the Rapidan River

I have one other photo of a pronggilled nymph that I took at an even earlier date.  This specimen is preserved, and it was found at Long Island Creek in Fluvanna County on 1/5.

________________________

P.S.  I feel more confident that the Limnephilid I found yesterday is genus Pycnopsyche.  For the key features of this particular genus, look back to my entry of 4/22.  On our specimen from yesterday, the "metanotal SA1 sclerites" are clearly present and not fused, and I think I can see the posterior sclerites on the lateral humps.   Here is a full view of the larva out of its case.  It is exactly 1 inch long!

On the genus of the Perlodid stoneflies I found -- I still feel uneasy with the call of Isoperla.  Nonetheless, the critical features for identification -- the "Y" shape of the mesosternal ridge, and the shape of the lacinia and the setae on the lacinia -- key it out to Isoperla or Clioperla.  The head pattern rules out Clioperla.

Exhilaration and Frustration: A Day at the Rapidan

As I always do, I found some wonderful insects today at the Rapidan River.  But I was frustrated by two of my nymphs when I got down to the work of genus level identification.  One of the "problem children" -- the Perlodid stonefly pictured above.  It's beautiful, and I was sure I had found Perlodid genus number 6.  But when I keyed it out with my microscope, anatomically, it checks out as an Isoperla.  This looks nothing like the Isoperla that I'm used to seeing (see previous entries).  Still there are many, many species in this wide-ranging genus.  I'll keep working on this one.  But if there's anyone out there who can help pin it down -- to genus and species, or correct me on the genus ID -- please feel free to chime in.  Here's another look.

The other insect that thrilled me was this huge Limnephilid (Northern Case-maker) caddis.  This case is slightly over 1 inch in length.

Very, very cool!  I was hopeful of coming up with the genus ID.  I think it's Pycnopsyche -- but I'm not 100% sure.  As I've noted before, genus ID of Limnephilids is a difficult process, and I don't feel confident that I found the sclerites on the lateral humps that I wanted to find.  I also had problems pulling this one out of its case.  But, I'm determined to work on this some more.  Here's another look at this case-maker when it was on its back in my tray.   You have to admit it -- that is one really neat case.

On to things that I could identify without any problem.   There's no reason to produce photos of all that I saw.  I had a very nice, very big, freeliving caddisfly -- a green one; and there were crane fly larvae in the leaf packs, and netspinners and flatheaded mayflies (all Epeorus) on the bottoms of rocks.  I also found a beautiful common stonefly (Perlid) on a rock, of which I did get a very good picture.  This is genus Acroneuria.

But once again, it was the leaf packs -- well, and some "root balls" that were covered with leaves -- that held most of the mayflies and stoneflies.  They were loaded -- it almost goes without saying -- with spiny crawler mayflies, genus Ephemerella.  Also flopping around in the leaves, some large brushlegged mayflies.  I saw small brushlegged mayflies when I was here in the winter, but clearly, these insects are really starting to grow.

I found two other stonefly families -- in addition to the Perlids and Perlodids that I've already mentioned.  First, there were a lot of Peltoperlids (Roach-like stoneflies) running around -- and they were big!  I'd say they're getting ready to hatch.    And I finally found one whose wing pads were tipped in black (this is the first time I've seen this) -- a sure indication that it's fully mature.

And the other stonefly family here represented was the Chloroperlidae -- the Green stonefly.  And I found a real beauty.

This is genus Sweltsa -- apparently Sweltsa lateralis (see Tom Murray's photo at http://bugguide.net/node/view/52785/bgimage).  This is the first time I've found a Chloroperlid in this stream, and I was a little surprised: I expect to find these only in small, mountain streams.  The Rapidan, where I look for insects, is already a pretty wide stream.  Still, it is clean and cold and running through completely forested land -- the other habitat features this insect prefers.

As I was leaving the Rapidan River, I thought to myself: "With so many wonderful insects in here, why bother going anywhere else?"  But then, I already know the answer to this one: different streams have different insects -- families and genera -- and I don't want to miss out on a chance to see something new.

Stream Report: Back to Buck Mt. Creek

So, what's your guess?  You need a close-up you say?  Glad to oblige: here's a microscope view.

Any ideas?  An alien from outer space?!  Actually, this is the pupa of a Net-winged Midge, and it is one wierd-looking critter.  When Rose and I saw one of these in the lab, we had no idea where to begin in terms of "keying" it out; we didn't even know what "order" to start with.  Fortunately our learned Director, John Murphy, had seen these before and knew what it was.  He sent us to p. 171 in Voshell (A Guide to Common Freshwater Invertebrates of North America), and right there it was.  There are a lot of these at the moment in Buck Mt. Creek, securely attached to the rocks.  But, there are still larvae around, so I was able to get a side-by-side pic of a larva and pupa.

I returned to Buck Mt. Creek to look for more Rhithrogenas (genus of flatheaded mayfly), and I did indeed find them: some pretty big, some pretty small.  This is not the only flatheaded genus I found.  I also found one Epeorus and one Leucrocuta.  I got a decent shot of the latter.

But on Rhithrogena -- what I hoped to get with my camera was a good look at the large, "suction cup" gills that form a complete oval on the underside of the nymph.  It can't be done.  The reason -- they're actually transparent and only show up with the contrast you can get in a microscope view.  So, here's a dorsal, live view of our insect, followed by a microscope view of the ventral side showing the gills.  It should be clear from this photo that the gills do indeed form a full loop.  (Note:  The "frilly" hairs that stick out on either side of the abdomen are not the gills.  This is "fibrilliform" that is either on top of the gills or -- more likely -- underneath: I have to check.)

Dorsal, live:

Ventral (abdomen only), microscope view:

Pretty neat!  I found two other things of interest.  The first is that, as I did last time, I found some tiny small minnow mayflies, and this time I did get live photos.  Let me show you two different nymphs.

I was quite happy: finally, some live pix of Heterocloeon nymphs (the genus I found last week).  I kept both nymphs so I could verify the genus at home -- I'm afraid I was disappointed!    These are not Heterocloeon -- there is no "large pigemented area" in the center of the gills; the gills are veined.  So, they're either genus Baetis or genus Acentrella (the other "two-tailed" genera) -- I just couldn't tell.   The difference between them?  Baetis nymphs have metathoracic wing pads; Acentrella nymphs do not.  I'll check back in a few weeks to look for bigger specimens -- these were very, very small.

My final point -- the taxon of the day was clearly the spiny crawler mayfly.  They were all over the place in every size and color  (all genus Ephemerella).  Here's a photo of two that lined up side-by-side in my dish.

I've noted before, that spiny crawlers like to live in the moss that grows on the rocks.  But, there were no such rocks in the riffles I sampled.  So, where did I find them?  Some were simply crawling around on the bottoms of rocks, but most were in leaf packs!   One wad of leaves and twigs that I pulled out of the water was literally crawling with them.  Two photos follow.  The first is a pic of the ball of leaves; in the second -- a close-up -- you can clearly see two of the resident nymphs.  (Click on the photo to enlarge the image.)

Of course there were other things in the stream.  I found water pennies, common netspinners, fingernet caddisflies (genus Chimarra), one Nemourid stonefly (genus Amphinemura), and a number of Isoperla Perlodids.  In fact, let me close with a photo of a Rhithrogena flathead and an Isoperla Perlodid that moved together and posed.