The following photo shows a tiny spider carcass (~3/16″ long) that was inside an exuvia (~1 3/4” long) from a Common Green Darner dragonfly (Anax junius). The exuvia was collected on 17 June 2021 from a small pond in Prince William County, Virginia USA. I discovered the spider long afterward — too late to save its life.
Thanks to Eva Weiderman and Joseph Girgente — members of the “Odonate Larvae and Exuviae” Facebook group — for their help in identifying the specimen as a jumping spider, Family Saticidae.
Salticidae is one of several families of spiders with eight (8) eyes. My take-away from reading the reference on BugGuide entitled “Spider Eye Arrangements” is identification of this specimen to the genus and species level is challenging at best and impossible at worst.
In contrast, it’s well known that spiders use odonate exuviae for shelter. I wish the jumping spider had come out of its most excellent hidey-hole sooner!
“Raynox DCR-250 close-up filter” is a blog post in which I provide more information about how I use the Raynox with my Panasonic Lumix superzoom bridge cameras.
The mystery item featured in my last blog post is a Christmas tree ornament hanging above a battery-powered flashlight with a low-power incandescent bulb.
Perhaps the bigger mystery is what makes the gold propeller inside the ornament spin around when the flashlight is powered-on.
Christmas tree ornament hanging above a flashlight.
Energy Transformations
When I taught 8th grade Physical Science classes, “energy transformations” was an overarching theme in one of the lab manuals for the course.
The Rayovac No. H22 Industrial Flashlight (shown above) uses two 1.5 V D-cell batteries to power a 2.4 V incandescent bulb. When the flashlight was powered-on and placed below the Christmas tree ornament, the following energy transformations occured.
potential energy → chemical energy → electrical energy → radiant energy → thermal energy → kinetic energy
Knowing that kinetic energy can be thought of as energy of motion, the question remains: What gives the spinning propeller its kinetic energy?
Heat Rises
How many times have you heard this common misconception? “Heat,” more correctly referred to as “thermal energy,” flows from higher to lower concentration of thermal energy, regardless of directions such as up or down. So what causes the propeller to spin?
Thermal energy from the incandescent flashlight bulb causes the temperature of the air around the flashlight bulb to increase. The warm air around the bulb is less dense than the surrounding air so it rises; the rising air current causes the gold propeller inside the Christmas tree ornament to spin. It’s worth noting I removed the plastic “lens” from the face of the flashlight head so it wouldn’t block airflow from the light bulb to Christmas tree ornament.
The Backstory
The Christmas tree ornament shown above is a treasured memento from my early childhood. My parents bought two similar ornaments: one is blue with a gold propeller; the other is green with a red propeller (not shown).
One of the ornaments was a gift for my sister; the other was for me. I can’t remember which one was given to me. In my defense, that was a long time ago — I might have been as young as three or four years old when we got the ornaments. That said, I remember clearly how fascinated I was with the spinning propeller inside the ornament!
At that time, Christmas tree lights were relatively large colored incandescent bulbs that got uncomfortably warm-to-hot when powered-on. When my Christmas tree ornament was hung above one of those lights, the propeller spun much faster than it did when hanging above the smaller flashlight bulb used for my demonstration.
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.
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