Archive for the ‘Photoshop’ Category

Tramea carolina exuvia

January 22, 2020

I’m a man on a mission to demystify identification of odonate exuviae, as I’m fond of saying. Easier said than done. In my experience, the process of identification can be challenging at best and impossible at worst.

For example, it’s nearly impossible to differentiate exuviae from the Genus Tramea (Saddlebags) to the species level.

The search for reliable larval characters to distinguish species of Tramea has generated considerable confusion in the literature. Source Credit: Landwer, Brett & Sites, Robert. (2006). Diagnostic efficacy of morphological characters of larval Tramea lacerata Hagen and Tramea onusta Hagen (Odonata: Libellulidae). Great Lakes Entomologist. 38. 155-163.

More recently, Tennessen cited the preceding research as well as a follow-up article by the same authors in 2010, and wrote…

…specific identification is still problematic. Source Credit: Tennessen, Kenneth. (2019). Dragonfly Nymphs of North America – An Identification Guide. Springer International Publishing. 567.

The fact of the matter is the most reliable way to identify odonate larvae to the species level is to rear them to maturity and emergence. Since an exuvia is essentially a nearly perfect shell of the last instar, it can be used to identify other specimens of the same species by pattern matching.

Rearing an unknown species of larva from genus Tramea

A larva from the Genus Tramea (Saddlebags) was collected by Andy Davidson near Richmond, Virginia USA, and reared to maturity. The following photo shows the adult dragonfly soon after emergence.

Photo used with permission from Andy Davidson.

The image was rotated in order to get a better look at the shape of the “saddlebags” on the rear wings of the dragonfly.

Photo used with permission from Andy Davidson.

The following composite image — created by Ed Lam, author and illustrator of Damselflies of the Northeast — clearly shows the difference in the shape of the saddlebags for Carolina- versus Red Saddlebags. Look closely at the saddlebags in the full-size version of the preceding photo and you can see the pattern perfectly matches the Carolina Saddlebags in Ed’s image, shown below.

Composite image used with permission from Ed Lam.

Look-alikes: Genus Pantala and Genus Tramea

Two genera from the Family Libellulidae (Skimmers) look similar: Genus Pantala (Rainpool Gliders); and Genus Tramea (Saddlebags). If you find an exuvia with long “tail fins,” then it might be a member of one of these two genera.

A Spot-winged Glider dragonfly (Pantala hymenaea) exuvia was collected by Andy Davidson near Richmond, Virginia USA.

A Carolina Saddlebags dragonfly (Tramea carolina) larva was collected by Andy Davidson near Richmond, Virginia USA, and reared to maturity. Andy saved the exuvia after emergence.

The following couplet from Identification Keys to Northeastern Anisoptera Larvae, compiled by Ken Soltesz, can be used to differentiate exuvia from Genus Pantala and Genus Tramea.

p. 37, Key to the Genera of the Family Libellulidae
12a – Superior abdominal appendage (epiproct) as long as, or longer than inferiors [paraprocts]. Pantala
12b – Superior abdominal appendage (epiproct) shorter than inferiors [paraprocts]. Tramea

What are the take-aways?

If you find an exuvia from the genus Tramea, then you might be unable to identify it to the species level.

I collected a Tramea sp. exuvia during Fall 2016 from a water retention pond located at a small park in Fairfax County, Virginia USA. I keyed out the specimen and identified it as Tramea carolina, in part, because Carolina Saddlebags had been observed in numbers at the same location. Am I certain of the identity? Yes and no. I’m certain the specimen is from genus Tramea; I’m reasonably sure (but not certain) it’s T. carolina. That said, my rationale is fairly good.

Related Resources

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Tramea carolina exuvia (ventral)

January 20, 2020

Carolina Saddlebags dragonfly (Tramea carolinaexuvia was collected by Andy Davidson near Richmond, Virginia USA. Carolina Saddlebags is a member of Family Libellulidae (Skimmers).

This individual might be a female, as indicated by what appears to be a small rudimentary ovipositor located along the margin between abdominal segments eight and nine (S8-9).

Related Resources

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Tramea carolina exuvia (dorsal)

January 17, 2020

Carolina Saddlebags dragonfly (Tramea carolinaexuvia was collected by Andy Davidson near Richmond, Virginia USA. Carolina Saddlebags is a member of Family Libellulidae (Skimmers).

Related Resources

Tech Tips

The subject was photographed against a pure white background using the “Meet Your Neighbours” (MYN) technique. The exuvia was “staged” on a clear plastic surface raised ~1.5 in (~3.81 cm) above the white background.

Information about both the photo gear that I used to shoot this photo, as well as detailed practical advice for using the MYN technique is available in the following blog post: MYN – Hagenius brevistylus exuvia (dorsal).

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Tramea carolina exuvia (face-head-dorsal)

January 15, 2020

A Carolina Saddlebags dragonfly (Tramea carolina) exuvia, collected by Andy Davidson near Richmond, Virginia USA, was photographed against a pure white background using the “Meet Your Neighbours” (MYN) technique. Carolina Saddlebags is a member of Family Libellulidae (Skimmers).

Tech Tips

The subject was “staged” on a clear plastic surface raised ~1.5 in (~3.81 cm) above the white background. As I speculated in my last blog post, increased distance between the stage and the background seems to have resulted in improved exposure of clear features such as the “eyes.”

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Sometimes it works; sometimes it doesn’t.

January 13, 2020

A Shadow Darner dragonfly (Aeshna umbrosa) exuvia, collected and identified by Andy Davidson near Richmond, Virginia USA, was photographed against a pure white background using the “Meet Your Neighbours” (MYN) technique.

Sometimes the MYN technique works; sometimes it doesn’t work as well. For example, this specimen has clear “eyes” that are clearly shown in the first photo and mostly blown out in the last photo.

I’m fairly certain this problem can be solved by “staging” the subject on a clear surface raised above the white background. In this case, the subject is only a few millimeters above the background. Further experimentation is planned.

Related Resource: Pop quiz: Sex the exuvia.

Copyright © 2020 Walter Sanford. All rights reserved.

Pop quiz: Sex the exuvia

January 10, 2020

An odonate exuvia was photographed against a pure white background using the “Meet Your Neighbours” (MYN) technique.

This specimen is a Shadow Darner dragonfly (Aeshna umbrosa) exuvia, collected and identified by Andy Davidson near Richmond, Virginia USA. Shadow Darner is a member of Family Aeshnidae (Darners).

Can you tell whether the exuvia is from a female or male larva? (Hint: The Related Resource, shown below, might be a helpful reference.)

Related Resource: Post update: Aeshna umbrosa exuvia.

Copyright © 2020 Walter Sanford. All rights reserved.

Post update: Aeshna umbrosa exuvia

January 8, 2020

Male odonates have two sets of sex organs: primary genitalia located on abdominal segment nine (S9); and secondary genitalia located on abdominal segments two-to-three (S2-3).

Closer examination of some test shots of the following Shadow Darner dragonfly (Aeshna umbrosa) exuvia, photographed on 02 December 2018, showed both sets of vestigial genitalia are clearly visible on the ventral side of this specimen.

Aeshna umbrosa (mating pair)

All odonates (dragonflies and damselflies) have a 10-segmented abdomen, numbered from front to back. Male dragonfly secondary genitalia, called hamules, are located in segments two and three (S2 and S3); female genitalia in segment eight (S8). Male and female dragonflies form the mating wheel in order for their genitalia to connect during copulation.

A. umbrosa (in wheel). Photo used with permission from Patrick Boez.

Related Resource: Test shots: Aeshna umbrosa exuvia.

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Hagenius brevistylus exuvia (ventral)

January 6, 2020

An odonate exuvia was photographed against a pure white background using the “Meet Your Neighbours” (MYN) technique.

This specimen is a Dragonhunter dragonfly (Hagenius brevistylus) exuvia. Dragonhunter is a member of Family Gomphidae (Clubtails).

Dorsal view update

I’ve made the same mistake twice recently: When in doubt, the “model” should face the camera! In my opinion, the following updated photo looks better than the version that shows the model facing away from the camera (published in my last blog post).

Ventral view

This individual is a female, as indicated by the rudimentary ovipositor located along the boundary between abdominal segments eight and nine (S8-9).

Related Resources

Tech Tips

The first two photos were taken using the same MYN Field Studio setup described in detail in my last blog post.

The last photo was taken by swapping the Godox TT685F fill flash for my Canon MT-26EX-RT Macro Twin Lite. The Canon flash was set for a power ratio of 1/32.

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Hagenius brevistylus exuvia (dorsal)

January 3, 2020

An odonate exuvia was photographed against a pure white background using the “Meet Your Neighbours” (MYN) technique.

This specimen is a Dragonhunter dragonfly (Hagenius brevistylus) exuvia. Dragonhunter is a member of Family Gomphidae (Clubtails).

Dragonhunter is the largest of North American clubtails; accordingly the large size and shape of a Dragonhunter exuvia is so distinctive that it’s relatively easy to identify to the species level.

Notice the large, paddle-like antennae. They remind me of ping pong paddles.

Related Resources

Tech Tips

The following equipment was used to shoot the macro photographs featured in this post: Fujifilm X-T1 digital camera; Fujifilm MCEX-11 extension tube; and Fujinon XF80mm macro lens minus the lens hood. The camera was set for both manual exposure and manual focus. That’s right, a switch on the camera body is used to set the type of focus. It’s a Fujifilm thing.

Godox X2TF radio flash trigger, mounted on the hotshoe of my X-T1, was used to control two off-camera external flash units set for radio slave mode.

  1. Godox TT685C Thinklite Flash for Canon Cameras (manual mode), fitted with a “Vello Bounce Dome (Diffuser) for Canon 580EX II Flash,” was used to light the underside of the translucent white plastic background; the top of the flash unit was ~30 cm from the bottom of the white plastic.
  2. Godox TT685F Thinklite Flash for Fujifilm Cameras (manual mode), fitted with a Lastolite Ezybox Speed-Lite 2 flash modifier, was used to light the subject from above.

Adobe Photoshop CC 2017 was used to spot heal and sharpen the image.

Practical Tips for the MYN Technique

A piece of opaque white plastic that is 12″ square is used for the background/”stage.” Actually, the white plastic background appears to be translucent when back-lighted by a flash unit at a relatively close distance.

The flash unit used to light the underside of the translucent white plastic background (Group A) was set for 1/2 +0.3 power; the zoom was set for 50mm in order to spread the beam of light sufficiently to avoid a hotspot on the white plastic background. The top of the flash head was ~10 inches from the bottom of the white plastic “stage.”

Next, take a test shot using only one flash — the flash that’s used to light the underside of the white background. Look at the histogram to check for correct exposure. You should see a spike on the far right side of the histogram that indicates the background is exposed properly (255, 255, 255).

Apple Aperture | Adjustments | Histogram

One or more flash units can be used to add “fill flash” from above the background/stage, as necessary. In this case, I used one flash (Group B) set for 1/64 power.

Use the 1:1 rule-of-thumb to determine how close/far to position the flash unit from the subject. The diagonal distance across the face of a softbox should be the distance to the subject [or less] for soft wrap-around light. Actually, the distance should be as close as possible without the softbox showing in the photo frame. Greater distances will result in a contrasty look.

For example, my Lastolite softboxes are 8.5” x 8.5” square (12” diagonally) so they should be one foot (1’) or less from the subject. In this case the front diffuser panel of a single softbox was placed ~6-8″ from the face of the specimen, off-set slightly to the left of the subject (facing forward).

MYN Field Studio setup

The following photo shows a behind-the-scenes look at one configuration of my Meet Your Neighbours Field Studio setup.

Meet Your Neighbours Field Studio setup, staged at BoG Photo Studio.

The exuvia is staged on the top from a clear plastic delicatessen container. This helps to reduce/eliminate the MYN “halo effect” by raising the subject a few millimeters above the white background.

There’s a flash that’s placed on a black plastic shelf below the white background/stage. It’s an old “bed shelf” from Bed Bath & Beyond that I repurposed for the MYN Field Studio.

Everything is mounted on a Promaster Deluxe Light Stand LS-2n using the following Manfrotto articulating arms and clamps.

Copyright © 2020 Walter Sanford. All rights reserved.

Top Pix of 2019

January 1, 2020

The following gallery shows my “Top Pix of 2019.” (See what I did there?) 28 photos are presented in chronological order beginning in February 2019 and ending in December 2019.

As you will see, I declare 2019 is/was unofficially “Year of the Gray Petaltail (T. thoreyi).”

01 FEB 2019 | Cordulegaster sp. larva (preserved specimen) | face

18 FEB 2019 | “Generic Baskettail” larva (preserved specimen) | face

28 FEB 2019 | BoG Photo Studio | Valentines Day rose

16 APR 2019 | Northern Virginia | Uhler’s Sundragon (male)

21 MAY 2019 | PNC. William County, VA | Arrowhead Spiketail (female)

21 MAY 2019 | PNC. William County, VA | Painted Skimmer (female)

21 MAY 2019 | PNC. William County, VA | Gray Petaltail (male)

21 MAY 2019 | PNC. William County, VA | Gray Petaltail (female)

29 MAY 2019 | PNC. William County, VA | Gray Petaltail (male)

14 JUN 2019 | PNC. William County, VA | Arrowhead Spiketail (female)

14 JUN 2019 | PNC. William County, VA | Gray Petaltail (male)

21 JUN 2019 | PNC. Wm. County, VA | Black-shouldered Spinyleg (female)

21 JUN 2019 | PNC. William County, VA | Common Sanddragon (male)

09 DEC 2019 | BoG Photo Studio | Common Green Darner | exuvia (face)

13 DEC 2019 | BoG PS | Common Green Darner | exuvia (anterior)

16 DEC 2019 | Richmond, VA | Spot-winged Glider | exuvia (face)

18 DEC 2019 | Richmond, VA | Spot-winged Glider | exuvia (dorsal)

20 DEC 2019 | Richmond, VA | Genus Celithemis | exuvia (face)

27 DEC 2019 | Richmond, VA | Genus Celithemis | exuvia (dorsal)

Copyright © 2020 Walter Sanford. All rights reserved.


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