Tuesday, August 30, 2011

Montana Insects, Part III.: Baetidae (Small Minnow Mayflies)

I found very few stoneflies when picking up nymphs and larvae during my trip to Montana: 2 Perlids (common stoneflies), a few small Perlodids (only one that I could ID, and some small Giants.  But I did find a whole lot of mayflies: pronggilleds, flatheads, spiny crawlers (perhaps the dominant taxon of the insects I found), and a lot of small minnow mayflies.

I expected to have a lot to say about the identity of the small minnow mayflies that I collected -- as it turns out, I will say very little.  Having looked at all of my nymphs with the microscope, I can say that almost every one is genus Baetis, and almost every one, I think, is the same species -- but I don't want to guess what species that is.

Most Baetis nymphs have three tails; clearly visible hind wing pads; and labial palps that are rounded with a small "thumb".  Let's look at some pictures.

All of the nymphs in the pictures below keyed out as Baetis, exhibiting all of these features.

My reason for thinking these are all the same species is the fact that they seem to have two features in common: 1) a common abdominal pattern, and 2) the tails/cerci lack "medial banding" -- they are clear in color, darkening only at the tips (look again at the microscope photo above).

However, I clearly did find one Baetis nymph that was not the same species.   This I discovered with microscope study, and I could not find a "live" photo that matched it for sure.  In the photo below I've placed two nymphs side-by-side.  The one on the right (viewer's right) is the common pattern we see; the one on the left isn't the same -- it may be B. flavistriga.  And note that there is medial banding on the tails of this nymph.

In closing, I did find two nymphs that I don't think were Baetis.  They have only two tails and no visible hind wing pads.  Since I did not see any fore coxal gills, I'd guess they were Acentrella.  But I'll have to continue to work on identification.

Now back to the streams of Virginia!

Monday, August 29, 2011

Montana Insects, Part II.: More Species That I've Never Seen in Our Streams

1. And what do we have here?  When I see "tusks" on a mayfly nymph I think of a "burrower": in this case I was sure I had found a Potamanthidae -- a "Hacklegill Mayfly."  So I submitted this photo, along with some others, as "Potamanthidae" to Bugguide.net.    Brady Richards moved the photos to Leptophlebiidae (Pronggilled mayfly), genus Paraleptophlebia!  If you've been reading this blog, you know that Paraleptophlebia is the most common genus of Pronggilled mayfly we see in our streams in central Virginia.  But -- we never see tusks.  Apparently there are Pronggilled species out West that do have tusks -- and the nymph in the photo above clearly does have "pronged" (= forked) gills.  Always new things to learn.

2. No problem here, it's a flatheaded mayfly (family: Heptageniidae).  But what about genus?  This one I figured out on my own: it's Nixe.   This is a common nymph in the West that hatches -- following Knopp and Cormier (Mayflies, p. 150) -- (if this is Nixe simplicioides) from the end of July till the end of September.  Note that morphologically, this genus is very close to Leucrocuta, the flathead we saw here a lot in the spring.  Neither genus has fibrilliform behind the gill on segment 7.  But Nixe nymphs have "intrasegmental setae" (fine hairs) on their tails -- Leucrocuta nymphs do not.  Peckarsky (Freshwater Macroinvertebrates, p. 31) does list this as a genus that occurs in the East, but I've never seen one in our local streams.

3. In my last entry, I showed you pictures of three large, beautiful spiny crawler mayflies, all genus Drunella (they're the ones with the "tubercles" on the leading edges of the fore femora).   Here's another Drunella, one that's oddly colored and oddly shaped.   Using photos already posted on Bugguide.net, we can identify this as Drunella doddsii.  I found this little fellow in Rock Creek, east of Missoula, on Monday, 8/22.  I don't think this species occurs in the East.

4. Common netspinner (Hydropsychidae), genus Arctopsyche.  Again, Peckarsky (Freshwater Macroinvertebrates, p. 101) lists this as a genus that occurs in the northeast: I've only seen it in my trips to Montana.  It's fairly large, normally dark green, and is identified by examining the shape of the "gula".  The gula is on the underside of the head and separates the two sides of the "chin" -- as it were, where they come together.  On Arctopsyche nymphs the gula is clearly visible, and narrows from top to bottom, as we can see in the photo below.

5. Now, how about this one?

Obviously, given the gills on the underside of the tummy, another common netspinner.  But I really wondered about the genus since I've never seen a netspinner with these colors before.  Turned out to be Hydropsyche, one of the most common genera we see in this part of the state!  Still, the colors are very special on this Montana version.

6. Not the best of photos, but one of the few Perlodid stoneflies I saw.  This is genus Isogenoides.  Peckarsky (Freshwater Macroinvertebrates, p. 71) lists it as a Perlodid we have in the East, and I know it's attested in Virginia.  Still, to date, I've never seen this genus outside of Montana.  This is a genus that is keyed out in two ways.  1) It has submental gills.

And 2) "[The] median ridge of [the] mesosternum extends anteriorly beyond [the] fork of [the] Y to [the] transverse ridge." (Peckarsky, p. 71)  Photo please.

Below -- setting off for a day of fishing on the Blackfoot River, north of Missoula, MT.

Saturday, August 27, 2011

Montana Insects, Part I.

I've just returned from a week in Montana where the main item on the agenda was 5 days of fly fishing for trout.  The fishing was great.  But I did take a few pictures -- well, more than a "few"! -- of insects.  It's early for me to make any kind of report, but I want to post some beautiful photos of beautiful stonefly and mayfly nymphs.

The "common stonefly" pictured above -- Perlidae -- is, I'm told Claassenia sabulosa, a species that's only found in the West:  its presence has been attested in Arizona, Colorado, Montana, Saskatchewan, and Utah.  I found this one (it was around 2 inches long, by the way) in Rock Creek, 25 miles east of Missoula.  Here's a close-up shot of the head, where the row of spinules across the "occipital ridge" (back of the head) stands out prominently.

Stunning colors and patterns!

Next, three spiny crawler mayflies -- big ones, about 1 inch in length -- all genus Drunella, all different colors, and all three were found in Grant Creek, a small stream that flows right through Missoula.

Finally, another spiny crawler (Ephemerellidae), but a species that isn't found in the East -- Timpanoga hecuba.  This hatches in the fall as a large, reddish mayfly that provides good fishing for fly fishermen.
Note the large "operculate" gills on segment 4 that cover the gills on segments 5-7.

Much, much more to follow, including many shots of small minnow mayflies -- that I hope to identify to genus level before I write up an entry.

Tuesday, August 16, 2011

Off to Montana

No, this isn't Virginia.  It's the Bitterrroot River flowing out of the Bitterroot range of the Rockies, south of Missoula, Montana.  This is where I'll be fishing next week.  It's the annual fly fishing trip with three of my very best friends.  The bad new is -- there won't be any blog entries posted next week: the good news is -- I'll be taking my camera and sampling gear to look for some of the species of mayflies, stoneflies, and caddisflies that are different than those we find in the East.

But first, a quick report on my trip to the Moormans today.  I went back to see if I could find some of the small minnow mayflies I found last week that I think might be Heterocloeon petersi (see the previous entry).  No luck.  I did find small minnow mayflies, but I just found the same species I've been seeing in other streams at the moment: Heterocloeon curiosum and Baetis intercalaris.  These:

(And yes, most of the Baetis intercalaris nymphs that I've found have been this small!)  I also saw common netspinners, fingernet caddisflies, brushlegged mayflies -- small and large -- common stoneflies (genus Acroneuria), and quite a few "tiny" flatheaded mayflies.   The "larger" flatheaded mayflies included this beautiful Epeorus vitreus.

Love those gills!  I also found a snail that we never find in big numbers -- a "Physid," the most common "lunged" snail we find in our streams.  Remember that most lunged snails open on the left when the narrow part is on top.

This Physid was larger than those that I normally see, also also darker in color. Most Physids are yellow, with gray spots or "freckles," this one was brown with yellow spots.  I suspect the color change has something to do with age.  Here it is moving its way around the tray.

That about wraps it up for the day and the week.  Time to leave behind the small streams of Virginia and head out to the "Big Sky" -- and "Big Water" -- country.

Sunday, August 14, 2011

Two More Species of Small Minnow Mayflies (Baetidae)?

On Thursday, 8/11, I posted this photo of a small minnow mayfly I had just found in the Moormans, noting that I was unsure of the species ID.  Having done some research this morning and looked closely at this nymph using my microscope, I now think I know what it is -- and "think" is the operative word.  In fact, I now think I found two new species of small minnow mayflies in the Moormans last week: Heterocloeon petersi -- pictured above -- and Baetis flavistriga, pictured below.

Let me first make the argument for Heterocloeon petersi, which, I have reason to believe, is uncommon.
My source notes a number of things for ID that require a more powerful microscope than I possess, so I have to focus on features that I can see.  1) As with many -- but not all -- Heterocloeon species, petersi nymphs have "procoxal gills".  This nymph clearly has them.

2) The abdominal segments are grey or grey/brown with "light" margins, and there is no dorsal pattern.   These features show up very well in this photo.

3) It's also worth noting that nymphs of this species are fairly large, and this one measured about 7mm in length, excluding the tails.  (That's big in the "Baetidae" world.)

Now, I remind everyone that I'm an "amateur" here -- I cannot be sure of my ID.  But, for the moment at least, H. petersi would be my guess.  Another look.

Now on to this little fella (no gender ID intended!).

This nymph is tiny -- but B. flavistriga nymphs do not get very big (4-6 mm).  The caudal filaments (tails) on B. flavistriga nymphs have a dark medial band, which is clear from the photo -- but that's fairly common with Baetis species.  So, my proposed ID is only based on the one distinguishing feature that I can discern:  there should be two "kidney shaped spots" toward the bottom edge of each abdominal tergite (segment).  I think I see them.

Based on what I can see -- there are features of the labial palpi that I don't know how to recognize -- I'd suggest that this is a Baetis flavistriga nymph.  But as with the H. petersi identification, this is hypothetical, and if a reader can confirm these ID's or disprove them, I'd be grateful for the help.

Should these ID's prove correct, then these two species of small minnow mayflies must be added to the "small minnow mayflies of summer" discussed in my entries of 8/6 and 8/8.  Below, another look at, possibly, H. petersi.

Friday, August 12, 2011

Same Old, Same Old -- With One Important Exception: Back to the Rivanna at Crofton

Let's start with the exception.  This is a common stonefly -- family Perlidae -- but this is the first time I've seen this genus since I started this blog.  Genus Agnetina.  I've seen these stoneflies only one place in our watershed and only one time before -- in the Rivanna last summer.  I was delighted to see this one today.  It was a small nymph, 1/4" to 1/2" in length, but note how fully colored it is, and the wing pads are starting to bow.

How do we recognize this Perlid genus?  There are two things that we have to see.  1) There must be an occipital ridge (line at the back edge of the head) with "a closely set regular row of spinules" (Peckarsky, Freshwater Macroinvertebrates, p. 69).  Can we see that using a microscope?

For sure.  (Actually, this "ridge" is visible on the photo at the top of the page if you double-click on the photo to enlarge it.)  2) There must be "branched subanal gills present," and the "basal cercal segments [are] without an inner fringe of long hairs" (same source, same page).  (Also, enlarge the picture at the top of the page to see how they "branch".)

There are "spiky hairs" at the base of the tails (cercal segments), but no "fringe of long hairs".  So, genus Agnetina.  This is, by the way, a relatively "intolerant" Perlid genus (0 to 2, depending on species) -- so what's it doing in the Rivanna?

The other insects I found today are all things I've found here (Crofton) before.  Still, I got some very nice photos.  I'll just post the photos with some general comments.

1. Calopterygidae (Broad-winged damselfly) -- a beauty!

2. Coenagrionidae (Narrow-winged damselfly) --also a beauty.

3.  And now -- a double!  The broad-winged and narrow-winged side-by-side in the tray.  Photos like this should help monitors to tell the two apart.  The differences are rather dramatic.

4. An Emerald dragonfly (Corduliidae).  I saw so many of these today that I started to brush them off the rocks so I could focus on other things.  And they're getting big!

5. A gorgeous flatheaded mayfly, genus Maccaffertium; very unusual colors (has it recently molted?).  I've not yet worked on species ID for this genus of flathead: something to keep for the future.

6. The "not unexpected" small minnow mayfly, Heterocloeon curiosum.

7. And last but not least, I found a number of Tricos (Little Stout Crawler mayflies).  My goal this summer was simply to find one: my goal now is to find one that isn't covered in silt!

Actually, I preserved this one, and the microscope photo reveals more detail -- and a good look at the "triangular operculate gills" -- than the live shot.

Below -- a picture of the Rivanna River below Crofton bridge in normal, summer flow.