The mystery item featured in my last blog post is a Beetle Spin® 1/8 oz fishing lure.
Beetle Spin® 1/8 oz fishing lure.
Perhaps the bigger mystery is how the fishing lure ended up where I found it, stuck in the bark of a tree (about head height) quite a distance from a small stream that might be fish-less. There was no fishing line attached to the lure. Anyway, there it was.
Beetle Spin® is one of the classic all-purpose fishing lures that is a nice addition to my tackle box.
One way to differentiate Emerald from Skimmer larvae/exuvia is to look for a “ventromedial groove” in the prementum: it’s probably Corduliidae (Emeralds) if there is a ventromedial groove; it’s probably Libellulidae if there isn’t.
Look closely at a version of the preceding photo that was reformatted, rotated, and cropped to show an enlarged view of the prementum. You should notice a ventromedial groove on the basal half of the prementum, indicating this specimen is a member of Family Corduliidae (Emeralds).
One reason I underexposed the photo is to add definition to the ventromedial groove and avoid overexposing the black background.
I prefer a white background for photographing odonate exuviae. Using a black background proved to be more challenging than I expected. More later in a follow-up blog post.
My last blog post was a “sketch pad” of test shots of an exuvia from a Comet Darner dragonfly (Anax longipes) collected by Stanley Caveney on 19 July 2021 from a pond at MeadowWoods in West Elgin, Ontario, Canada. All of the shots in that post are unedited JPGs straight from my camera. This post features edited versions of the RAF (raw) files from that photo shoot, including some images with value-added annotations.
I used Adobe Photoshop to create a composite image that features the best parts of two photos from the sketch pad.
This specimen is from a male Comet Darner, as indicated by its vestigial primary- and secondary genitalia. The inset photo shows a clear view of the vestigial hamuli (secondary genitalia) that are partially obscured in the background photo.
All of the shots in this post are unedited JPGs straight from my camera, with the exception of the first ventral view (cropped to remove a distracting element from the composition).
Lateral view
I started with a lateral view of an exuvia from a Comet Darner dragonfly (Anax longipes) exuvia collected by Stanley Caveney on 19 July 2021 from a pond at MeadowWoods in West Elgin, Ontario, Canada.
The next two photos show my frustratingly poor attempts to pose the specimen for shots of the ventral side of the exuvia. Every time I positioned the subject the way I wanted, it rolled over before I could take a shot!
The two shots combined show the vestigial primary- and secondary genitalia that indicate this specimen is from a male Comet Darner. Yeah, I know it would help to annotate those parts of its anatomy, but that’s the next step. In the meantime, please follow the embedded hyperlink shown above and you might be able to figure out what I’m saying.
The last photo shows a closer view of the prementum. My goal was to get a better look at the labial palps. Again, annotations would help, but if you know what I’m talking about then you can see the palpal lobes are squared off.
The horn is clearly visible in the last photo. Notice there are three “bumps” located between the eyes of the exuvia: the middle bump is the horn; the antennae bases are located to the left and right of the horn.
If so, then I’m guessing D. transversa larvae are bottom dwellers, as indicated by the dirty, sediment-covered dorsal side and relatively clean ventral side of this specimen.
The nymphs are sprawlers that cling to roots or hunker down in sediments of mixed sand and silt particles. Source Credit: K. J. Tennessen, Dragonfly Nymphs of North America, https://doi.org/10.1007/978-3-319-97776-8_10, Macromiidae, p. 330.
The Backstory
The preceding photos were shot using the prototype for a homemade curved clear plastic tray intended for staging subjects against a white background.
With a few minor tweaks, the curved stage performed better than during initial testing. I needed to add a second external flash unit to more evenly illuminate the white background.
Although I’m fairly satisfied with the results of these test shots, more testing is required to be sure the set-up is working the way I want.
I have been working on the prototype for a homemade curved clear plastic tray that is intended for staging subjects against a white background.
My goal for Thursday: Test the prototype stage using a toy mini-lizard as the model for some test shots, and if the proof-of-concept were established, substitute an odonate exuvia for the toy lizard and shoot another set of photos.
16 SEP 2021 | BoG Photo Studio | toy mini-lizard
Well, you know what they say about the best laid plans! First, a line of fairly strong thunderstorms moved through the region where I live so I had to shut down my computer equipment. Second, the Washington Football Team played the New York Giants on Thursday Night Football so I had to watch the game. That’s right, had to watch. Turns out it was time well-spent.
Bottom line: I never finished the test shots of the toy lizard, and of course that means I didn’t shoot any photos of a real scientific specimen.
The curved surface of the clear plastic stage caused reflections from the single external flash that was used to light the subject. I had just figured out a work-around when the thunderstorms rolled in: I took 14 test shots; only the last one (shown above) is usable. I hadn’t intended to create a photo with a pure white background, but it was easy to adjust the image exposure during post-processing.
The Backstory
What’s my motivation? Many macro photographers use insect pins for mounting small subjects like odonate exuviae. I think there’s a big problem with that technique: The position of the pin is permanent. In other words, if the pin is attached to the ventral side of the specimen then it’s challenging at best and impossible at worst to take clean, clear shots of that side of the subject. I don’t want to use insect pins because some of my specimens are one of a kind.
For quite some time, I’ve been experimenting with the use of flat clear plastic stages as a solution for this problem. I think a curved stage might be a breakthrough, but more testing is required to be sure.
For example, notice the color fringing near the tip of the lizard’s tail — I’m not sure what caused that problem in only one part of the photo, therefore I don’t know how to fix it. Yet.
The Common Green Darner dragonfly (Anax junius) exuvia was collected on 17 June 2021 from a small pond at an undisclosed location in Prince William County, Virginia USA.
The Comet Darner dragonfly (Anax longipes) exuvia was collected by Stanley Caveney on 19 July 2021 from a pond at MeadowWoods in West Elgin, Ontario, Canada.
Taxonomy
There are five species of dragonflies in the Genus Anax for the United States and Canada: Amazon Darner (Anax amazili); Common Green Darner (Anax junius); Comet Darner (Anax longipes); Giant Darner (Anax walsinghami); and Blue-spotted Comet (Anax concolor).
Common Green Darner and Comet Darner are the only species from the Genus Anax found where I live in Northern Virginia USA.
This specimen is from Family Aeshnidae (Darners), as indicated by the following field marks: the exuvia has a flat labium that doesn’t cover the face (not mask-like); the antennae are thin and thread-like (not club-like, as in Gomphidae larvae/exuviae); and the eyes are large relative to the size of the head.
Stanley Caveney is shown in the first of several photos taken by Hugh Casbourn. Stan contacted me for confirmation of his tentative identification of several Comet Darner exuviae that he collected during July 2021. Stan kindly gave one of the exuviae to me.
Photo used with written permission from Hugh Casbourn.
I asked Stan whether he had taken photographs of the Comet Darner exuviae in situ. Stan hadn’t, so he and Hugh revisited a local pond where they searched for and found two more exuviae.
How many exuviae do you see in the next photo? Look closely — both cast skins are shown in the same image.
Photo used with written permission from Hugh Casbourn.
An exuvia from a female Comet Darner appears in the foreground of the preceding photograph…
Photo used with written permission from Hugh Casbourn.
and a male Comet Darner appears in the background.
Photo used with written permission from Hugh Casbourn.
I asked Stan for advice regarding where to look for Comet Darner exuviae.
The six exuviae found to date were mainly at the inner edge of the cattail beds, facing the open water of the pond and where the individual cattail plants were spaced out. Source Credit: Personal communication from Stanley Caveney.
Editor’s Note: Sincere thanks to Derek Caveney, Stan’s son, for shipping the exuvia to me. The specimen was packed so carefully that it arrived in excellent condition, as you can see in the first photo in this blog post. I’m looking forward to shooting a complete photo set of the exuvia.
walter sanford's photoblog 