Posts Tagged ‘Gomphurus vastus’

Cobra Clubtail external reproductive anatomy

May 28, 2017

I liked to make paper- and plastic models when I was a child. Seems like the directions for assembling many models — not that anyone reads the directions — always started by saying something like “Insert Tab A in Slot B.”

Oddly enough, that line reminds me of how odonates copulate, in general, and Cobra Clubtail dragonflies (Gomphurus vastus) in particular.

Male

The hamules are “Tab A.”

Female

The subgenital plate is “Slot B.”

Putting it all together

Insert Tab A in Slot B. That’s the PG-rated version of how Cobra Clubtail dragonflies copulate in order to reproduce.

The Backstory

There is an annual mass emergence of Cobra Clubtails during the first week-or-two of May at Riverbend Park. It’s a spectacular event worth seeing firsthand!

The following photo shows a dead female, one of several Cobra Clubtails that were trampled by groups of elementary school children visiting the park on 09 May 2017. Her premature death saddens me because it was avoidable — the students should have been warned to watch their step because there were lots of Cobra Clubtails perching on the ground almost everywhere.

In the hope the female didn’t die in vein, I reluctantly decided to photograph the corpse in order to illustrate her external reproductive anatomy.

Editor’s Note: Sincere thanks to Dennis Paulson for help in identifying the female parts on the ventral side of abdominal segments eight and nine (S8-9).

Copyright © 2017 Walter Sanford. All rights reserved.

Because it’s fun!

May 16, 2017

Why do I hunt odonates, that is, dragonflies and damselflies? I like being outdoors, visiting beautiful natural places. I like honing my skills as a wildlife photographer. Most importantly, it’s fun! I like the challenge of finding uncommon species, and the thrill of making new discoveries.

A Cobra Clubtail dragonfly (Gomphurus vastus) was spotted along the Potomac River at Riverbend Park, Fairfax County, Virginia USA. This individual is a male, as indicated by his terminal appendages and indented hind wings.

The male was perching on colorful kayaks stored in a wooden rack near the boat ramp. Notice the natural coloration of the dragonfly was affected by light reflected from the kayaks. That’s OK since this photo set is all about fun, right?

09 MAY 2017 | Riverbend Park | Cobra Clubtail (male)

Can you say “hamules?” Males of many species in the Family Gomphidae (Clubtails) have prominent secondary sex organs.

09 MAY 2017 | Riverbend Park | Cobra Clubtail (male)

09 MAY 2017 | Riverbend Park | Cobra Clubtail (male)

09 MAY 2017 | Riverbend Park | Cobra Clubtail (male)

09 MAY 2017 | Riverbend Park | Cobra Clubtail (male)

09 MAY 2017 | Riverbend Park | Cobra Clubtail (male)

Tech Tips: I carried two digital cameras during the trip to Riverbend Park: a Panasonic DMC-FZ150 superzoom bridge camera plus Canon 580EX Speedlite, my go-to kit for photowalking; as well as my Fujifilm X-T1Fujinon XF55-200mm zoom lens, and Fujifilm EF-X500 shoe mount flash. Since Fujifilm digital cameras are well-known for capturing vivid color, the X-T1 was the camera of choice for this colorful scene.

Editor’s Note: 16 May is the one-year anniversary of my first visit to Riverbend Park to see the annual mass emergence of Cobra Clubtail dragonflies that occurs during the first two weeks in May.

Copyright © 2017 Walter Sanford. All rights reserved.

Malformed Cobra Clubtail dragonflies

February 21, 2017

I took 255 photographs during my first photowalk along the Potomac River at Riverbend Park, Fairfax County, Virginia USA, including lots of photos of Cobra Clubtail dragonflies (Gomphurus vastus). I noticed several malformed individuals when I reviewed the entire photo set recently (in search of look-alike species of clubtail dragonflies). None of the malformations prevented the dragonflies from functioning normally.

The first Cobra Clubtail is a male with a slightly crimped right hind wing, where a small part of the wing failed to fully inflate during emergence.

The next individual is a female. Notice that abdominal segment seven (S7) was crimped during emergence. (All dragonflies and damselflies have a 10-segmented abdomen, numbered from front to back.)

The last individual is a male. Notice his left front leg is missing. The male is either malformed or he lost the leg due to injury.

A Cobra Clubtail dragonfly (Gomphurus vastus) spotted at Riverbend Park, Fairfax County, Virginia USA. This individual is a male; its left front leg is missing. Two dark face bars are field markers that can be used to differentiate Cobra Clubtail from other similar looking species of clubtails.

16 MAY 2016 | Riverbend Park | Cobra Clubtail (male, missing leg)

Two thick dark face bars are field markers that can be used to differentiate Cobra Clubtail from other similar looking species in the Family Gomphidae (Clubtails): Midland Clubtail (Gomphus fraternus) has no face bars; Splendid Clubtail (Gomphus lineatifrons) has thin dark face bars.

Tech Tips:

Shutter Priority mode was used for the first two photographs. Aperture Priority mode was used for the last photo, in order to increase the depth of field. As you can see, the depth of field at f/7.1 was insufficient for the tip of the dragonfly abdomen to be in focus. Typically, I wouldn’t publish the last photo, but I made an exception because it is the only photo I took that shows the face bars clearly.

Copyright © 2017 Walter Sanford. All rights reserved.

Gomphurus vastus exuvia

February 17, 2017

10s, maybe 100s of adult Cobra Clubtail dragonflies (Gomphurus vastus) were spotted on 16 May 2016 during a photowalk along the Potomac River at Riverbend Park, Fairfax County, Virginia USA. Cobra Clubtails were the only species of odonate observed in a period of several hours.

A Cobra Clubtail dragonfly (Gomphurus vastus) spotted at Riverbend Park, Fairfax County, Virginia USA. This individual is a male.

No. 1 | 16 MAY 2016 | Riverbend Park | Cobra Clubtail (adult male)

A single exuvia (shown below) from an unknown species of dragonfly was collected with permission from park staff. If adult Cobra Clubtail dragonflies were common, then the specimen is probably a Cobra Clubtail exuvia, right? Let’s test our hypothesis.

A Cobra Clubtail dragonfly exuvia (Gomphurus vastus) collected at Riverbend Park, Fairfax County, Virginia USA.

No. 2 | Cobra Clubtail (Gomphurus vastus) | exuvia (face-head)

A two-step process was used to identify the genus and species of the exuvia.

  1. Determine the family.
  2. Determine the genus and species.

Step 1. Family

First, determine the family of the specimen. For reference, watch the excellent Vimeo video, Identifying dragonfly larva to family (8:06). Here’s the decision tree used to identify the exuvia as a member of the Family Gomphidae (Clubtails).

  • The specimen has a flat labium that doesn’t cover the face (not mask-like). [See Photo No. 3.]
  • Antennae are club-like (not thin and thread-like, as in Aeshnidae). [See Photo No. 3.]
  • Eyes not exceptionally large compared to the size of the head (not large, as in Aeshnidae). [See Photo No. 3.]
A Cobra Clubtail dragonfly exuvia (Gomphurus vastus) collected at Riverbend Park, Fairfax County, Virginia USA.

No. 3 | Cobra Clubtail (Gomphurus vastus) | exuvia (face-head)

(See a full-size version of the original photo, without annotation.)

Step 2. Genus and species

Gomphidae is the second largest family of dragonflies, so it can be challenging to identify some specimens to the genus and species level.

Characters from two dichotomous keys were used to identify the exuvia, in part, due to confusion caused by the fact that the name for the genus to which Cobra Clubtail belongs was changed recently from Gomphus to Gomphurus. As a result, the workflow for identifying this specimen was a little “jumpier” than usual.

dichotomous key: a key for the identification of organisms based on a series of choices between alternative characters. Source Credit: Merriam-Webster Dictionary.

Dichotomous Key 1

Identification Keys to Northeastern Anisoptera Larvae, compiled by Ken Soltesz. Cobra Clubtail (Gomphus vastus), p. 15, Key to the species of the genus Gomphurus.

  • 1a – Strongly hooked palpal lobes with few teeth (3-5). Gomphurus group I (2) [See Photo No. 8.]
  • 2a – Length 27-30 mm. (vastus) [See Photo No. 4, below.]
A Cobra Clubtail dragonfly exuvia (Gomphurus vastus) collected at Riverbend Park, Fairfax County, Virginia USA.

No. 4 | Cobra Clubtail (Gomphurus vastus) | exuvia (dorsal)

(See a full-size version of the original photo, without annotation.)

Dichotomous Key 2

“Gomphus complex” (= Gomphini) – Clubtails, Odonata Nymphs of Michigan.

  • 1b. Middorsal length of Ab9 [S9] less than half its basal width (fig); length of Ab10 [S10] < 0.50x its width (fig) – 6 [See Photo No. 6.]
  • 6b. Lateral spines of Ab9 close to Ab10, markedly longer than those on Ab8 (fig) [S8]; abdomen appears dorsoventrally flattened (fig) – Gomphurus, 8 [See Photo No. 6.]
  • 8b. Apical margin of median lobe of prementum straight or slightly convex (fig) – 9 [See Photo No. 8.]
  • 9a.(8b). End hook of lateral lobe of labium strongly incurved, extending far past apex of the truncate, 3 to 4 lateral teeth next to it (fig) – Gomphurus vastus

No. 5Cobra Clubtail (Gomphurus vastus) | exuvia (posterior)

The preceding photograph shows a wider view of the posterior end of the abdomen. A closer view of the anal pyramid helps to illustrate several of the morphological characters described in Dichotomous Key 2.

No. 6Cobra Clubtail (Gomphurus vastus) | exuvia (anal pyramid)

(See a full-size version of the original photo, without annotation.)

The basal width of abdominal segment nine (S9) was measured in a straight line from edge-to-edge across the abdomen. The same distance would be longer if it were measured along the joint between abdominal segments eight and nine (S8 and S9). Either way the basal width is measured, the middorsal length is less than half of the basal width.

Since the middorsal length of abdominal segment 10 (S10) is clearly less than its basal width, the character wasn’t illustrated in the preceding annotated image.

Looking carefully at the anal pyramid, notice the cerci (sing. cercus) are slightly shorter than the epiproct, and the epiproct is almost as long as the paraprocts.

A Cobra Clubtail dragonfly exuvia (Gomphurus vastus) collected at Riverbend Park, Fairfax County, Virginia USA.

No. 7 | Cobra Clubtail (Gomphurus vastus) | exuvia (ventral)

Photo No. 7 shows a wider view of the ventral side of the specimen. Zooming in on the prementum helps to illustrate some of the morphological characters described in Dichotomous Key 2.

A Cobra Clubtail dragonfly exuvia (Gomphurus vastus) collected at Riverbend Park, Fairfax County, Virginia USA.

No. 8 | Cobra Clubtail (Gomphurus vastus) | exuvia (prementum)

(See a full-size version of the original photo, without annotation.)

Tech Tips:

The following equipment was used to shoot all of the preceding photographs: Canon EOS 5D Mark II digital camera, in manual mode; Canon EF100mm f/2.8L Macro lens (set for manual focus) plus a Kenko 20mm macro automatic extension tube; Canon 580EX II external flash, off-camera, in manual mode; Canon 580EX external flash, off-camera, in manual mode; and a Yongnuo YN-622C-TX E-TTL II Wireless Flash Controller for Canon plus a two-pack of Yongnuo YN-622C II E-TTL Wireless Flash Transceivers for Canon.

Raynox DCR-250 close-up filter was used for Photo No. 3, 6, and 8. A Canon Extender EF 1.4x II was used for more magnification in Photo No. 8. Adding the tele-extender results in a 1 f/stop loss of light; additional backlight was added to the scene using a Nissin i40 external flash unit (off-camera, in SF mode).

Adobe Photoshop CC 2017 was used to annotate selected images.

The following photograph of another dragonfly exuvia was taken in-situ along the shoreline of the Potomac River using a Panasonic DMC-FZ150 superzoom bridge camera and Canon 580EX Speedlite, my go-to kit for photowalking. There were many exuviae clinging to the concrete retaining wall shown in the photo. Photo No. 1 was taken using the same camera-flash combo.

A Cobra Clubtail dragonfly exuvia (Gomphurus vastus) photographed in situ at Riverbend Park, Fairfax County, Virginia USA.

No. 9 | 16 MAY 2016 | Riverbend Park | Cobra Clubtail (exuvia, in situ)

Related Resources:

Editor’s Note: Sincere thanks to Sue Gregoire, Kestrel Haven Migration Observatory, for her kind mentorship. Sue patiently provides guidance regarding the scientific jargon that can make it either challenging (at best) or impossible to understand many dichotomous keys for the identification of odonate larvae/exuviae. Like every good teacher, Sue doesn’t “give me a fish” — she teaches me how to fish. Thanks again, Sue!

Copyright © 2017 Walter Sanford. All rights reserved.


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