Friday, June 29, 2012
I've been out two days in a row, and both days I've well come back essentially empty-handed. Well, I did find this beautiful Baetis pluto small minnow mayfly in Buck Mt. Creek yesterday. Actually, I found a lot of insects in Buck Mt. Creek -- but no Acentrella nadineae. And this morning, at the Moormans in Sugar Hollow, I thought I finally had one: it turned out to be a female Plauditus dubius! I'm not sure why I didn't notice the banding at the back of the tails.
Still, there are some things to report. First -- on the "unknown" small minnow mayflies I found at the Moormans on Tuesday, this gorgeous nymph turned out to be another H. curiosum, just one that was still immature. I saw that right away when I got home, where, using the microscope, I could plainly see the procoxal gills at the base of the front legs.
And there's another way we can make this ID, by noting the abdominal pattern: segments 3-5 are pale in color, so too are segments 9 and 10.
The very small nymph that I found on Tuesday -- this one (bottom)...
appears to have been a mature Acentrella turbida small minnow mayfly. That's the way it keys out: there is a dense row of setae on the dorsal margins of the femora, the tibia and tarsi (see Beaty, "The Ephemeroptera of North Carolina," p. 4). I have just one hesitation on this decision: this nymph measured only 3 mm in length, mature A. turbida should be 4-6 mm. Still, I can't find anything else it might be.
Now the "looking ahead" part of this entry. At Buck Mt. Creek yesterday, the other thing of interest I found was an immature "broad-winged damselfly" nymph -- family, Calopterygidae.
Since we'll be seeing a lot of broad-winged damsels in the Rivanna River this summer, I thought I might try my hand at species ID using the great key that I just found on line, "The Odonata larvae of Michigan," for which go to: http://insects.ummz.lsa.umich.edu/michodo/mol/Home.htm. The key page you'll want to visit is: http://insects.ummz.lsa.umich.edu/michodo/mol/Hetaerna.htm.
That the broadwinged damselflies in our local streams are Hetaerina in genus, we can tell by looking at the prementum.
How far is the prementum "cleft" from the "base of the prementum"? If it is almost halfway to the base, the genus is "Calopteryx," if it's closer to the base of the palpal lobes, it's "Haeterina." So, we're clearly looking at a Haeterina nymph. (For genus ID, see Barbara Peckarsky, et.al., Freshwater Macroinvertebrates, p. 46.)
Now using our "Key to Mature Larvae of Michigan Hetaerina" -- our choices are H. titia or H. americana. On H. titia nymphs there are "prominent sharp tubercles on [the] postero-lateral margin of [the head]: on H. americana, the "tubercles on postero-lateral margin of [the] head [are] low and blunt." Let's have a look:
I'd call those low and blunt. There's another key test: on H. titia nymphs, the "gills [are] distinctly banded"; on H. americana, they "are not banded as above, except perhaps on [the] margins." On the nymphs I've collected, there is only marginal banding.
Our "Key" adds that H. americana is "fairly common in the LP [Lower Penninsula of Michigan]." Looks to me like they're fairly common in central Virginia as well. Still, this is something I'll continue to look at as the summer proceeds.
Below: another look at that beautiful Baetis pluto.
Tuesday, June 26, 2012
A quick trip to the Moormans on Free Union Rd. this afternoon, and I was reminded of why I don't go to streams in the afternoon in the summer: it's too difficult to get photos. With the sun high in the sky it's virtually impossible to shoot straight down on your subject: you're always creating a shadow! But I did find some nice insects, and lots and lots of small minnow mayflies.
But we start (the photo above) with a beautiful spiny crawler. This is the one we see in the summer -- Serratella serratoides -- but I've never seen one before with such beautiful colors. Another shot:
I should run through the full species description -- and I'll do that one of these days -- but the critical feature to see: "a transverse row of four black dots on each sternite; often with speckling on [the] last few sternites in some specimens" (Beaty, "The Ephemeroptera of North Carolina," p. 31). Here you go:
I found two S. serratoides spinys today, the second was a drab brown which is the color I normally see.
And now for the small minnow mayflies. I saw two species I recognized without any trouble -- but I have three insects that will require identification. Fortunately, we have a boiling hot weekend in store: great time to work in my lab in the basement where it's always cool.
The two small minnows I knew: Baetis intercalaris (did not take a picture) and Heterocloeon curiosum. I think most of the small minnows I saw were H. curiosum. A couple of photos.
The three that will require some work are these:
1) A reddish/brown nymph -- with a leg missing. In the first photo, it lined up next to one of the H. curiosums.
2) A beautiful nymph which posed nicely for photos. I feel like I should know this one: the gills look like it's a Heterocloeon.
3) A tiny, but fully mature, nymph, with hairy legs like we find on Acentrella, but it's only 3 mm long.
The larger one at the top is, again, the reddish brown nymph on which I need to work.
Monday, June 25, 2012
One of the small minnow mayflies I found yesterday in the Rivanna at Darden Towe Park (Charlottesville) was a new species for me: Iswaeon anoka. This was formerly known as Heterocloeon anoka, but in 2008, Guenther and McCafferty elevated Iswaeon to the status of genus (Steven Beaty, "The Ephemeroptera on North Carolina," p. 10).
The small minnow genus Iswaeon is described by Beaty in the following way:
"Genus Diagnosis: No procoxal osmobranchia; tibia narrow at base and distinctly widened medially to apically; claw with 2 rows of denticles with denticles in the first row about same length (except for first few); hind wing pads absent; two caudal filaments, median caudal filament of about 6 segments and slightly longer than abdominal segment 10." (Beaty, "The Ephemeroptera of North Carolina," p. 10)
There are three things in this description for which I cannot provide any photos. 1) The "procoxal osmobranchia" are the procoxal gills that are present on Heterocloeon curiosum nymphs (see the entry from yesterday): no sense in my taking a photo of something that doesn't exist. 2) The 2 rows of denticles on the claws can only be seen with 400X magnification. And 3) there are no hind wing pads, so again, I see no point in taking a picture of something that just isn't there.
But what is crucial in establishing Iswaeon identification -- according to Beaty -- is the tibia shape, and that the tibiae are narrow at the base and gradually widen, is easy to see from this microscope photo.
We can also see a close-up of the median caudal filament: it is indeed longer than abdominal segment 10.
Let's move to the species ID, and I'll go through Beaty's description section by section:
"I. anoka -- nymphs ~ 4 mm; a small, sometimes indistinct, dark dot at each tibial-femoral junction; a large, distinct dark spot laterally above the meso- and metanotal coxae." Those dots can be seen in this photo:
Beaty continues, "large median dark spots sometimes present on terga 2 and 6; midventral dark spots sometimes present on abdominal sterna 2-8 or 9." I'm not sure about the spots on terga 2 and 6, but there are certainly "midventral dark spots" on sterna 2-8. There are actually multiple spots visible on the sterna.
Beaty -- "dorsum of abdomen often with a pale median longitudinal stripe set against a darker background, sometimes reduced to small pale spots and interrupted on middle segments; caudal filaments with dark medial band."
The dark medial band on the caudal filaments (tails) is visible in the live photo at the top of the page. As for the pale longitudinal stripe on the dorsum "set against a darker background" -- if you enlarge the live photo, you can see a series of pale, longitudinal dash marks in the center of the terga. But the pale stripe against the dark background is very clear on segments 1-4 and 9-10 in this microscope shot.
I want to thank Steven Beaty for confirming my identification. I hope to return to the Rivanna tomorrow to find more of these nymphs and take better photos.
(For photographs of Heterocloeon anoka by Donald Chandler, go to: http://www.discoverlife.org/mp/20p?see=I_DSC233&res=640)
Sunday, June 24, 2012
I've been having trouble finding small minnow mayflies in most of the streams that I visit in the winter and spring: no problems today at the Rivanna. The Rivanna has been too high and off color for me to explore until now. But I could finally get in and look for some insects today. I saw three or four small minnow mayflies on the first rock I picked up, including the one in the photo above -- Heterocloeon curiosum.
This is a common small minnow in the Rivanna in summer; it's a species I hardly see anywhere else. You might recall from last summer that the distinctive trait of this species is the pair of forecoxal/procoxal gills. These:
Also distinctive is the dorsal pattern: most tergites are brown, with 4 and 10 being pale yellow. We have a good view of that in the photo below.
I can't say for sure that "sternal tracheation" -- note the gray tracheation on the mesosternum in the microsocope photo above -- is also a species characteristic, but it's something I normally see. Using size, forecoxal/procoxal gills, and sternal tracheation for definition, the three nymphs pictured below were also H. curiosum. But if that's true, I sure find the colors more than a little bit odd. (Well, number three might be all right.)
I think these require more work.
But I found more than H. curiosum this morning. Another small minnow that was easy to pick out by the tails -- a Baetis intercalaris.
And now we turn to the unknowns. I found three additional small minnow mayflies this morning that, so far, I have not ID'd, and I think they are three different species. Since I see no procoxal gills on any of them, they are probably Acentrella or Plauditus nymphs in terms of the genus. But at the moment, that's all I can tell you -- well, except that all three were small, 3-4 mm. Here they are.
Mystery Baetid 1: This one was fairly mature and had banded cerci. 4mm
Mystery Baetid 2: Cerci (tails) on this one were missing. 4mm
Mystery Baetid 3: The smallest of the lot -- only 3 mm in length.
The lab work on these may take me awhile. If I'm successful I'll be sure to post my results.
Finally, a special treat for me today: the first Calopterigidae of the season -- a "broadwinged damselfly."
I didn't keep it so I can't be sure of the genus. But the broadwingeds that I found last year were all Haeterina.
Saturday, June 23, 2012
This photo was taken on June 7th at the Lynch River, and in the entry posted that day, I pointed out that this Darner dragonfly was genus Boyeria based on the fact that the tips of the paraprocts curve inward (for Boyeria genus ID, see Barbara Peckarsky, et.al., Freshwater Macroinvertebrates of Northeastern North America, p. 27). In this entry, I'll try to get this down to species ID: this appears to be Boyeria vinosa, the common name for which is the "Fawn Darner."
We can make this ID using a resource that I found just yesterday: "Odonata Larvae of Michigan: Keys for, and notes on, the dragon and damselfly larvae found in the State of Michigan." You can find this online at: http://insects.ummz.lsa.umich.edu/michodo/mol/Home.htm, and for Boyeria species ID, the relevant keys are found at: http://insects.ummz.lsa.umich.edu/michodo/mol/Boyeria.htm. There we find the following words:
"Prementum width about 0.66x of its length, folded labium clear short of the posterior margin of mesocoxae; Ab5-9 with lateral spines; epiproct often cleft, clearly shorter than paraprocts. B. vinosa"
Fortunately, I had taken a photo of the prementum with the nymph on its back, and that photo shows us two of the things that we need to see. This is the picture.
Since I did not preserve the nymph, I can't get an "actual" measurement of the width and length of the prementum. But, I can determine the ratio from a physical print. If I've measured correctly, the width of the prementum (top edge) is 0.657x of its length. That's right on the money. But we can also see from this photo that the folded labium (the prementum and postmentum combined) does indeed end short of the "posterior margin of the mesocoxae (where the middle legs attach to the body)".
Without the actual insect, I cannot check for the "spines" on the abdominal segments, but we can see the paraprocts and the epiproct, and the epiproct is "cleft," and slightly shorter than the curved tips of the paraprocts.
I'd call that nymph Boyeria vinosa -- a Fawn Darner. The B. vinosa tolerance value is high: 5.8.
I think it's likely that the Darner I found yesterday at the Moormans was also a "Fawn," but I can't tell for sure since I did not photograph the prementum. But we can see the tail end from this photo.
A closer look:
From now on, I'll be taking prementum photos! And I do have a Darner dragonfly in my reference collection that might be a different species -- Boyeria grafiana. With B. grafiana nymphs, the "Prementum width [is] about 0.60x of its length, [and the] folded labium extends to [the] posterior margin of [the] mesocoxae, or beyond." The measurement here is 0.603 -- again, right on the money -- but I can't say that the labium extends all the way to the posterior edge of the mesocoxae. Darn close.
(For photos of adult B. vinosa dragonflies, go to: http://bugguide.net/node/view/4301/bgimage?from=24.)
Note: In using the "keys" today, I have struggled to understand the difference between the "prementum" and the "labium," in Odonata. My understanding at the moment -- and remember, I'm an amateur -- is that the "labium" includes the "prementum" and the "postmentum," and it is hinged (I think the "hinge" is the pale line at the end of the labium). It is the prementum that extends from the hinge to pick up food in the act of eating. If I find out that I'm wrong, I'll let you know. I wish the keys made this clear.