Semper Fidelis - Semper Discentes

Walk Along With Me

In Odonata on April 2, 2013 at 2:23 pm

As a dragonfly/beetle enthusiast (or “amateur odonatist-slash-coleopterist”, if you will), I remember how bored I got last winter.  All the bugs had died off, or retired to their buggy cribs to wait out the cold weather.  I had little to do but read, and wait for the springtime re-emergence of my spineless friends.

THIS year, however, I figured I’d hold back some of the specimens I collected during 2011, to give me something to do in curating and identifying them while the winds howled through my Ozark holler.  This is the first day of December–certainly not even wintertime in Missouri–but the thermometer hit 18 F. this morning while I was driving Susan up to catch the school bus at 7 AM.

So…I decided to pull out just ONE of the odonates I caught on my trip to Montana last summer, and take YOU, gentle reader, through the cobwebby passages of my thought processes as this rank amateur attempts to pin down the identity of this little bug.

First, a word on the collection information:

I caught this animal at 1:00 PM, on July 21, 2011, in Lewis and Clark County, Missouri, in a roadside stream on Interstate 15, north of Helena, at milepost 198, elevation 3697′.  46.67461N, 112.01188W.  I assigned it my collection number D110721014.  D=dragonfly/damselfly.  110721=July 21, 2011.  014=the 14th specimen I caught that day.

So far, so good. 

I then slipped the little fellow out of the glassine envelope, where he’d rested for over four months.  Immediately after capture, I had placed the specimen in a glassine triangle, marked on the outside with the letter “R”, which represented Site “R” for the trip.  I also placed a slip of paper inside the triangle, marked with an “R” in pencil (pencil marks don’t tend to fade or become obliterated when soaked in acetone), so that I could be sure that the correct animal would always be correlated with the correct collection data, which I entered into my fieldbook, also labelled “R”.  I made sure the triangle was closed tightly and dropped the whole thing into a Mason jar of acetone.

(Since the Montana trip, I’ve modified my collection procedure somewhat, and now keep the triangles, with the live bugs inside, in a small tin box for a couple of hours, to allow the specimens to void their gastric contents, before putting the triangle into the acetone overnight.)

Okay.  Now the bug’s been sitting in a glassine envelope, with an index card listing all the collection data, since July.  I’ve entered all the collection data, including the collection number, and all the location data, into an Excel spreadsheet with holds all information pertaining to my odonate collecting.  I’ve left the columns “Name” and “Common Name” blank, until today (I hope!).

I look over the bug now, for the first time in months.  The first thing I notice is, “This is a damselfly”. 

Ladies and Gentlemen, THIS is a damselfly!

Pretty basic, but now I’ve eliminated a whole lot of dragonfly species from my identification efforts.  Most people can easily tell the difference, as the damselflies are much more delicate than their more robust cousins, and this particular specimen holds its wings parallel to its body, eliminating two of the three common families–the Calopterigidae (broadwings) and Lestidae (the spreadwings).  I’m now pretty sure I’ve got a member of the Family Coenagrionidae–the pond damsels, and a group that is a BEAR to identify.

I next notice that this is a MALE. 

Notice the ventral swelling on the second abdominal segment? “Congratulations, Sir. It’s a BOY!”

He has the diagnostic ventral swelling of secondary genitalia on the early abdominal segments.

Males are USUALLY a bit simpler to identify, since they don’t usually exhibit a wide range of morphological variation within species.  I also notice that he’s quite a bit SMALLER than the damselflies I’m accustomed to finding here in the Missouri Ozarks, so I measure him, finding him to be 28 mm in length, about an inch long.
 

Well, he’s been sitting in that envelope for over four months, and I manage to break off the abdomen during the measuring process; however, I retain both sections, and continue.

OK.  Now I start to think, “I found this specimen in a ‘roadside stream’ (rather than a pond)”.  In Missouri, most of the coenagrionids I find in MOVING (lotic) water are of the species Argia, while NON-MOVING (lentic)  lakes or ponds often yield Enallagma.  I don’t, however, know diddly-squat about Montana species, but am starting to lean toward eliminating Enallagma–the bluets–a horribly difficult genera to pin down.

I have no experience whatsoever with other genera in this family–Amphiagrion, Coenagrion, Ishnura, Nehalennia and Telebasis aren’t in my collection–and Amphiagrion, Nehalennia and Telebasis don’t appear to be common in my neck of the woods, but who knows about Montana?

Seems to me to be a good time to break out the reference books.  I COULD begin with a general key to all damselflies, such as would be found in Damselfly Genera of the New World or Damselflies of North America, and both of which are sitting before me on my computer table.  However, I first pull out Dennis Paulson’s Dragonflies and Damselflies of the West, and start casually looking through it, studying the range maps, and seeing if something jumps out at me.

Well, in checking over the generic descriptions, in Paulson’s book, I pause to read about “forktails” of the genus Ischnura:  “very small to small damselflies”, “‘Forktail’ refers to a forked projection at the end of S10 (the tenth, or last, abdominal segment) in males of most species.”  Hmmm.

Would you call this a “forked projection”?

I’ve been looking over the bug with a hand lens; now, my 60-year-old eyes can no longer pick up the details I need, so I put him under a dissecting microscope.  I take a few pictures with my idiot-proof, point-and-shoot digital camera, using the incredibly simple method of sorta mashing the lens up against the eyepiece of the microscope, and the subject loses his head in the process.

“The combination of green thorax and blue-tipped abdomen is mostly typical of forktails.”    

Green, striped thorax.

I check out a handy chart in Dr. Paulson’s book: Forktail (Ishnura) Identification, which lists THREE species with a combination of a) green, striped thorax, and b) S8-S9 (Abdominal segments 8 and 9) of males blue.  I immediately eliminate the Mexican Forktail, as it is found, as you might expect, in MEXICO, New Mexico, Arizona.  This leaves the Eastern Forktail and the Western Forktail.

HOWEVER, “[The Eastern Forktail] overlaps with…Western Forktails…as a major identification challenge.  Fortunately, there is another close-range field mark for males:  Eastern lacks tiny green spots on either side of prothorax present in Mexican and Western”. 

The bright green face is at the lower left, the postocular spots at the upper right.

 Moving right along, the book goes on to say that the Western Forktail has “face bright green, postocular (behind the eyes) spots bluish-green”.  I will, therefore, go out on a limb and declare that this is Ischnura perparva, the Western Forktail.

That little teardrop-shaped mark sure looks like a “tiny green spot” on the side of the thorax to me!   
 
Now comes the GUTSY part.  I’m gonna post this story right now.
 
THEN, I’m gonna e-mail Dennis Paulson, send him the story, and ask him to comment on my identification.  If I’m right, I will silently and humbly bask in my own glory.
 
If I’m WRONG, I’ll still keep the story, tell you what Dennis said, and let you appreciate just how much fun odonates are.
 
One hour later:
 
I AM DA MAN!!!!!!  Here’s the reply from Dennis Paulson:
 
Hi, George.

 
I would say you have followed the book’s instructions to the letter and (whew) come up with the correct identification. The tiny green spots on the prothorax are a good ID mark with which to distinguish these two when north of the range of the Mexican Forktail. Even better, the photo of the end of the abdomen of your specimen shows the more or less evenly forked paraproct (inferior appendage) of the Western Forktail. Note from the book that the lower fork is much longer in Eastern (p. 126).
 
Congrats! Now glue that head back on.
 
Dennis
 
I have now visited the major respository of odonate collection information, “Odonata Central” (www.odonatacentral.org), and have posted a record of my discovery.  I also glued the head back on.
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