Posts Tagged ‘exuviae’

Common Green Darner dragonfly (external female reproductive anatomy)

June 5, 2020

For some species of odonate exuviae, sex is indicated by a form of remnant reproductive anatomy. These external structures don’t look exactly the same for all species of dragonflies and damselflies, but their function is identical.

As far as I know, this is true for all species in the Family Aeshnidae (Darners) such as Common Green Darner dragonfly (Anax junius).

The following photograph shows a ventral view of a female Common Green Darner dragonfly. Notice the external reproductive anatomical structure on abdominal segment nine (S9) is virtually identical to the remnant anatomical structure on S9 of the exuvia, shown above.

Original photo used with permission from Louisa C. Craven.

The Backstory

My dear friend Louisa Craven discovered the lifeless adult dragonfly while on vacation with her family in Nags Head, North Carolina USA. Louisa is an accomplished wildlife photographer who developed an interest in odonates as a result of many photowalks with me.

Related Resources

Copyright © 2020 Walter Sanford. All rights reserved.

Cobra Clubtail versus Midland Clubtail

April 20, 2020

Odonate exuviae from two species in Genus GomphurusCobra Clubtail (Gomphurus vastus) and Midland Clubtail (Gomphurus fraternus) — are nearly perfect body doubles, with the exception of one key field mark that can be used to differentiate the species.

Dorsal views

Lateral spines are located on abdominal segments six through nine (S6-S9) for both species.

10 JUN 2019 | Barron County, WI | Midland Clubtail exuvia (dorsal)

Ventral views

The overall shape of the prementum is similar for both species.

10 JUN 2019 | Barron County, WI | Midland Clubtail exuvia (ventral)

Prementum (ventral view)

The shape of the palpal lobes on the prementum is different for the two species, as shown in the following diagram on p. 15, Key to the species of genus GomphurusIdentification Keys to Northeastern Anisoptera Larvae, compiled by Ken Soltesz.

The following images are magnified approximately three and one-half times life size (~3.5x).

For both species, focus on the row of teeth along the right palpal lobe. Notice the strongly curved shape of the palpal lobe for Cobra Clubtail (shown above), in contrast with the gently arched shape of the palpal lobe for Midland Clubtail (shown below). Also notice the Cobra palpal lobe has fewer teeth than Midland.

10 JUN 2019 | Barron County, WI | Gomphurus fraternus (exuvia)

Adults

Adult Cobra Clubtail dragonflies are almost identical to Midland Clubtails too. Several field marks can be used to differentiate the two species. In my opinion, one field mark is the easiest to recognize where it really matters — in the field!

16 MAY 2016 | Riverbend Park | Cobra Clubtail (adult male)

Notice there aren’t any mid-dorsal marks on abdominal segments eight and nine (S8-S9) for Cobra Clubtail (shown above). In contrast, there is a small yellow triangle on abdominal segment eight (S8) for Midland Clubtail (shown below). This is true for males and females of both species.

Photo used with permission from Freda van den Broek.

Copyright © 2020 Walter Sanford. All rights reserved.

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, that is, unless you’re fortunate to find a larva emerging in the field. 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.

“Odonate Larvae and Exuviae” Facebook group

November 29, 2019

I created a new Facebook group called “Odonate Larvae and Exuviae.” Readers of this blog who enjoy my photographs of odonate exuviae might be interested in following the new group. Please join us!

Copyright © 2019 Walter Sanford. All rights reserved.

Odonate exuviae collecting sites

July 29, 2019

The following video shows a “boater’s-eye view” of some sites where odonate exuviae have been collected by Joseph Johnston along Aquia Creek, located in Stafford County, Virginia USA. Joe is an avid boater and sport fisherman who kindly agreed to be my “Eyes on the Aquia,” always on the lookout for odonate exuvia to share with me.

The first photo gallery features still images of several spots shown in the preceding video. Joe estimates the water is ~5-6 feet deep outside the channel markers, and much deeper in the middle of the creek.

Joe’s boat is somewhere between the long boat docks (lower-right quadrant) and Government Island (near center), as shown in an aerial view of Aquia Creek provided by Google Maps.

The last photo gallery features still images of several exuviae, shown in situ before Joe collected the specimens. The first photo shows where it all began, when Joe collected his first dragonfly exuvia for me on 20 June 2018.

Related Resources

Credits

All media Copyright © 2019 by Joseph Johnston. Used with permission from Mr. Johnston.

Copyright © 2019 Walter Sanford. All rights reserved.

Composite image: Progomphus obscurus exuvia

February 4, 2019

The following focus-stacked composite image shows the exuvia from a Common Sanddragon (Progomphus obscurus) larva that was collected and reared by Bob Perkins.

I have 10s, maybe 100s, of Common Sanddragon exuviae in my collection, but have never seen one cleaner than this beautiful specimen. I didn’t realize P. obscurus larvae are so hairy!

Related Resource: More composite images: P. obscurus exuvia.

Tech Tips

11 photos were used to create the focus stack. A single focus point was positioned over select anatomical features, working from back-to-front; photos were taken at each point of interest.

The following equipment was used to shoot the preceding composite image: Canon EOS 5D Mark II digital camera, in manual mode; Canon MP-E 65mm Macro lens (set for f/11 at 3x); and Canon MT-26EX-RT Macro Twin Lite set for “Master” mode, and several external flashes set for “Slave” mode including Canon 580 EX- and Canon 580EX II Speedlites and a Godox TT685C Thinklite TTL Flash fitted with a Lastolite Ezybox Speed-Lite 2 flash modifier.

Auto power-off was disabled for the camera and all external flash units.

Adobe Photoshop CC 2017 was used to create the focus stack, as well as spot-heal and sharpen the final output.

Copyright © 2019 Walter Sanford. All rights reserved.

Top 10 Photos of 2018

January 2, 2019

The following gallery shows 18 finalists for my “Top 10 Photos of 2018.” The photos are presented in reverse-chronological order beginning in September 2018 and ending in February 2018.

As you will see, I declare 2018 is/was unofficially “Year of the Sable Clubtail (S. rogersi).”

No. 1

20 SEP 2018 | Fairfax County, VA | Pandora Sphinx moth

No. 2

23 AUG 2018 | Occoquan Bay NWR | Osprey (male, plus prey)

No. 3

No. 4

No. 5

No. 6

05 JUL 2018 | Fairfax County, VA | Sable Clubtail (female)

No. 7

No. 8

No. 9

12 JUN 2018 | Fairfax County, VA | Sable Clubtail (male)

No. 10

08 JUN 2018 | Fairfax County, VA | Sable Clubtail (male)

No. 11

06 JUN 2018 | Northern Virginia | Gray Petaltail (male)

No. 12

No. 13

No. 14

No. 15

No. 16

No. 17

No. 18

Editor’s Note: The following location codes are used in some photo captions, shown above.

Copyright © 2019 Walter Sanford. All rights reserved.

Test shots: Unknown odonate exuvia

December 12, 2018

An odonate exuvia from an unknown species of dragonfly (Anisoptera) was collected by a good friend during April 2018 in Vienna, Austria.

Based upon the crenulations along the margins of the labium, I think the specimen is a member of either the Family Corduliidae (Emeralds) or Family Libellulidae (Skimmers). I need to clean the anal pyramid for a clearer look at the terminal appendages in order to identify the family.

One-off

The first photo is a “one-off,” that is, not a composite image. The focus point is on the face mask/head; the rest of the subject is in soft focus.

Anisoptera (unknown species) | exuvia (face/head-dorsal)

Composite images

The next two “photos” are three-layer focus-stacked composite images: For each image, the focus point is on the face mask/head in the first photo; the thorax in the second photo; and the terminal appendages in the third photo. The entire body of the exuvia is acceptably in focus, including most of the legs.

The specimen has dorsal hooks on some abdominal segments (exact number unknown without closer examination), and lateral spines on abdominal segments eight and nine (S8-9).

Anisoptera (unknown species) | exuvia (dorsal)

I think this individual might be a female, as indicated by what appears to be a rudimentary ovipositor that is visible on the ventral side of abdominal segment nine (S9).

Anisoptera (unknown species) | exuvia (ventral)

Post Update

Sincere thanks to Benoit Guillon and Christophe Brochard, members of the “Dragonflies and Damselflies – Worldwide Odonata” Facebook group, for kindly identifying this specimen as an exuvia from a Downy Emerald dragonfly (Cordulia aenea). Downy Emerald is a member of the Family Corduliidae (Emeralds).

The following photo shows a plastic container of 20 Downy Emerald dragonfly (Cordulia aenea) exuviae, collected by a good friend during April 2018 in Vienna, Austria. Thanks to field marks shared by Benoit Guillon, I was able to quickly determine that all of the exuviae are the same species as the specimen featured in this blog post.

Related Resource: Cordulia aenea: exuviae (1/2), by Benoit Guillon.

Tech Tips

The following equipment was used to shoot all of the preceding photographs: Canon EOS 5D Mark II digital camera, in manual mode; Kenko 20mm macro automatic extension tubeCanon EF100mm f/2.8L Macro lens (set for manual focus); and Canon MT-26EX-RT Macro Twin Lite set for “Master” mode, and several external flashes set for “Slave” mode including Canon 580 EX- and Canon 580EX II Speedlites and a Godox TT685C Thinklite TTL Flash fitted with a Lastolite Ezybox Speed-Lite 2 flash modifier.

Adobe Photoshop CC 2017 was used to create the two focus-stacked composite images, as well as spot-heal and sharpen the final output.

Copyright © 2018 Walter Sanford. All rights reserved.

Test shots: Tachopteryx thoreyi exuviae

November 30, 2018

Two Gray Petaltail dragonfly (Tachopteryx thoreyi) exuviae were collected on 23 May 2018 by Walter Sanford near a forest seep at an undisclosed location in Northern Virginia USA. Gray Petaltail is a member of the Family Petaluridae (Petaltails).

Although both specimens are similar, they aren’t identical. For example, twin rows of hook-like structures are clearly visible on the dorsal side of the abdomen on the lower exuvia, and almost invisible on the upper exuvia. The upper exuvia is dirtier and appears to be more “worn” than the lower one. Notice the “schmutz” on the face of the lower exuvia, probably a piece of leaf litter.

Both individuals might be male, as indicated by vestigial hamules that appear to be visible on the ventral side of the specimens.

Test shots of the specimens were taken using a relatively small aperture of f/16 for greater depth of field. Each photo is a “one-off,” that is, not a composite image. Focus stacks will be created sometime in the near future, after the exuviae are rehydrated, cleaned, and posed for better composition.

Tech Tips

The following equipment was used to shoot both of the preceding photographs: Canon EOS 5D Mark II digital camera, in manual mode; Kenko 20mm macro automatic extension tubeCanon EF100mm f/2.8L Macro lens (set for manual focus); and Canon MT-26EX-RT Macro Twin Lite set for “Master” mode, and several external flashes set for “Slave” mode including Canon 580 EX- and Canon 580EX II Speedlites and a Godox TT685C Thinklite TTL Flash fitted with a Lastolite Ezybox Speed-Lite 2 flash modifier.

Adobe Photoshop CC 2017 was used to spot-heal and sharpen both images.

Copyright © 2018 Walter Sanford. All rights reserved.

Precious cargo

November 5, 2018

Odonates are aquatic insects. They spend most of their life as larvae that live in water; this stage of their life cycle can last from a few months to a few years. Finally, they emerge from the water and metamorphose into adults in order to reproduce; their offspring return to the water and the cycle begins again.

Careful and/or lucky observers will notice exuviae (sing. exuvia), also known as either “cast skins” or “shed skins,” left behind when odonate larvae emerge. Exuviae are fragile little works of natural art that are challenging at best to ship from one location to another.

The preceding photo shows a small plastic vial containing three odonate exuviae, received from Andy Davidson. All three exuviae are members of Family Libellulidae (Skimmers). From left-to-right, the following specimens can be seen inside the vial: Wandering Glider (Pantala flavescens); Eastern Pondhawk (Erythemis simplicicollis); Blue Dasher (Pachydiplax longipennis).

Andy packed the exuviae carefully inside a 15 ml centrifuge tube with a screw on/off cap; pieces of crumpled bubble wrap were used to separate the specimens inside the tube. A pair of tweezers was used to remove the bubble wrap. All three exuviae appear to be in perfect condition.

Editor’s Notes

Andy Davidson is a graduate student at Virginia Commonwealth University in Richmond, Virginia USA. Andy works with Dr. James Vonesh, his faculty advisor, and a team of researchers studying the ecology of James River rock pools. Andy’s research project is entitled “Predator-Prey Interactions in a Changing World.”

Sincere thanks to Andy for kindly sharing several exuviae saved from laboratory-reared odonate nymphs — I’m looking forward to creating new annotated identification guides for the specimens!

Copyright © 2018 Walter Sanford. All rights reserved.


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