Archive for the ‘digital photography’ Category

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.

Crayfish

May 26, 2017

A crayfish was spotted in the shallows of Bull Run, under several inches of water. I estimate it was 3-4 in (~7.6-10.2 cm) in length.

Many crayfish can be particularly hard to identify from a photograph and many new species are still being discovered in Virginia’s waterways. This large crayfish is from the Family Cambaridae and is likely a native species. Other crayfish found in Northern Virginia, like the rusty crayfish (Orconectes rusticus) and red swamp crayfish (Procambarus clarkii), were likely introduced via the food industry and pose a serious threat to native crayfish populations. Source Credit: John Burke, Ecologist III, Stormwater Management Branch, Fairfax County Department of Public Works and Environmental Services.

10 MAY 2017 | Fairfax County, VA | crayfish (underwater)

Notice the first, second, and third pairs of walking legs feature chelae (plural).

A chela /kˈiːlə/, also named claw, nipper, or pincer, is a pincer-like organ terminating certain limbs of some arthropods. The name comes from Greek (χηλή) through New Latin (chela). The plural form is chelae. Legs bearing a chela are called chelipeds. Source Credit: Chela (organ), Wikipedia.

Also notice the slimy stuff on the rocks that makes them super slippery!

The slimy, slippery coating you find on rocks in aquatic systems is periphyton. In freshwater systems, periphyton is mostly comprised of algae but other microorganisms and detritus also collect on submerged rocks. Periphyton serves as an essential food source to many aquatic organisms and can also act as a bioindicator, signaling changes in water chemistry and nutrient levels in the system (Chetelat et al. 1997). Source Credit: John Burke.

Tech Tip:  My Canon 580EX Speedlite external flash unit was set for 1/16 power in order to penetrate the water and illuminate the subject on a bright, sunny day.

Copyright © 2017 Walter Sanford. All rights reserved.

Eastern Hog-nosed Snake

May 24, 2017

The only downside — or upside, depending upon your point of view — to my new hotspot for hunting odonates is there are only two trails in/out and both paths are steeply-inclined. Going in, not so bad walking downhill; going out, not so much fun!

I stopped to catch my breath as I was walking up a long trail with a 45-degree slope. I heard a rustling sound in the vegetation on the left side of the trail, a little beyond where I was standing. I moved closer slowly until I spotted my first Eastern Hog-nosed Snake (Heterodon platirhinos)!

10 MAY 2017 | Fairfax County, VA | Eastern Hog-nosed Snake

Although the name for this snake is less than flattering, notice the distinctive orange fleur-de-lis shape on top of its head. The coloration of Eastern Hog-nosed Snake is variable; I was fortunate to see one of the more colorful ones.

10 MAY 2017 | Fairfax County, VA | Eastern Hog-nosed Snake

I never had a clear view of the entire snake, but I estimate it was two-to-three feet in length.

Copyright © 2017 Walter Sanford. All rights reserved.

The party’s over

May 22, 2017

Several Eastern Pondhawk dragonflies (Erythemis simplicicollis) were spotted during a photowalk along a mid-size stream in Fairfax County, Virginia USA.

10 MAY 2017 | Fairfax County, VA | Eastern Pondhawk (immature male)

For some types of dragonflies, immature males have the same coloration as females of the same species. This is true for many members of the Family Libellulidae (Skimmers) such as Eastern Pondhawk. Terminal appendages can be used to identify gender.

10 MAY 2017 | Fairfax County, VA | Eastern Pondhawk (female)

The Backstory

I visited a new location in Fairfax County, Virginia on 03 May 2017, following my hunch that the spot might be a good place to find some of the more uncommon species of odonates. Turns out my hunch was right!

I revisited the same location a week later. Let’s just say lightning didn’t strike the same place twice. I saw several Eastern Pondhawks but none of the uncommon species of odonates that I saw a week earlier. I don’t know whether it’s phenology or the fact that Eastern Pondhawks are voracious predators, but it seems like whenever they show up it’s game over for the uncommon species of dragonflies and damselflies that emerge during spring. By the way, that explains the title of this post.

When I see the first-of-season Eastern Pondhawks, I start singing “The Party’s Over” like Don Meredith used to at the end of Monday Night Football games on ABC-TV. Yes, I’m old enough to remember Dandy Don!

Related Resources:

Copyright © 2017 Walter Sanford. All rights reserved.

Ashy Clubtail dragonfly (male)

May 20, 2017

An Ashy Clubtail (Phanogomphus lividus) was spotted during a photowalk along a mid-size stream in Fairfax County, Virginia USA.

03 MAY 2017 | Fairfax County, VA | Ashy Clubtail (male)

This individual is a male, as indicated by his terminal appendages and indented hind wings.

03 MAY 2017 | Fairfax County, VA | Ashy Clubtail (male)

The last photo is uncropped. The wider view shows the Ashy Clubtail is well-camouflaged when perching on the ground.

03 MAY 2017 | Fairfax County, VA | Ashy Clubtail (male)

The Backstory

I visited a new location in Fairfax County, Virginia on 03 May 2017, following my hunch that the spot might be a good place to find some of the more uncommon species of odonates. Turns out my hunch was right!

I saw species from four families of dragonflies: male Stream Cruiser dragonfly (Didymops transversa); male Springtime Darner dragonfly (Basiaeschna janata); female and male Common Baskettail dragonfly (Epitheca cynosura); female and male Spine-crowned Clubtail dragonfly (Hylogomphus abbreviatus); at least two male Lancet Clubtail dragonflies (Phanogomphus exilis); and the male Ashy Clubtail (Phanogomphus lividus) featured in this post.

In addition, I saw lots of teneral damselflies from the Family Coenagrionidae (Pond Damsels), possibly Blue-tipped Dancer (Argia tibialis).

03 MAY 2017 | Fairfax County, VA | teneral damselfly

Copyright © 2017 Walter Sanford. All rights reserved.

Common Baskettail (terminal appendages)

May 18, 2017

A male and female Common Baskettail dragonfly (Epitheca cynosura) were spotted recently at the same location in Fairfax County, Virginia USA.

Male and female Common Baskettails look similar. Terminal appendages can be used to identify gender.

Male

Male dragonflies have three terminal appendages, collectively called “claspers,” that are used to grab and hold female dragonflies during mating: an upper pair of cerci (“superior appendages”); and a lower unpaired epiproct (“inferior appendage”).

03 MAY 2017 | Fairfax County, VA | Common Baskettail (male)

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

Female

Female dragonflies have a pair of cerci (superior appendages) that have little or no function. The abdomen of female Common Baskettails is noticeably thicker than males of the same species.

03 MAY 2017 | Fairfax County, VA | Common Baskettail (female)

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

A better view of the subgenital plate is provided by the following digital scan of the underside of the abdomen of a female Common Baskettail. The subgenital plate looks a little like a pair of calipers. Also known as vulvar lamina, the subgenital plate is located under the ninth abdominal segment (S9) of some female odonates and “serves to hold eggs in place during exophytic oviposition.” Remember that all dragonflies and damselflies have a 10-segmented abdomen, numbered from front to back.

Image used with permission from Ed Lam.

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.

Lancet Clubtail dragonflies (males)

May 14, 2017

At least two Lancet Clubtail dragonflies (Phanogomphus exilis) were spotted during a photowalk along a mid-size stream in Fairfax County, Virginia USA.

03 MAY 2017 | Fairfax County, VA | Lancet Clubtail (male)

These individuals are males, as indicated by their terminal appendages and indented hind wings.

03 MAY 2017 | Fairfax County, VA | Lancet Clubtail (male)

The next photograph was taken at a later time than the first two photos. All of the photos in this post were taken near the same location. Is this another male, or the same one featured in the preceding photos? Who knows?

03 MAY 2017 | Fairfax County, VA | Lancet Clubtail (male)

Lancet Clubtail versus Ashy Clubtail

Lancet Clubtail looks similar to Ashy Clubtail (Phanogomphus lividus). The only way to differentiate the two species with certainty is to examine their external reproductive anatomy; this is impossible unless the specimens are captured and examined in-hand.

Relative size is used sometimes to identify the two species: Lancet Clubtail is slightly smaller than Ashy Clubtail. There are two problems with this method of identification. First, it is virtually impossible to determine the exact size of a specimen in the field unless it is captured and measured. Second, some natural variation in size should be expected among individuals of the same species.

A quick-and-dirty method for differentiating Lancet- and Ashy Clubtails with some degree of certainty is to look at the markings on abdominal segments eight and nine (S8-9). Lancet Clubtail has a “spearpoint” on top of abdominal segment eight (S8) that almost reaches the end of the segment, a wide yellow stripe on top of segment nine (S9), and irregular yellow markings on the sides of segments eight and nine (S8-9).

03 MAY 2017 | Fairfax County, VA | Lancet Clubtail (male)

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

In contrast, Ashy Clubtail has a spearpoint on top of abdominal segment eight (S8) that is less than half the length of the segment, segment nine (S9) may or may not have a pale yellow stripe on top, and the sides of segments eight and nine (S8-9) may or may not have “poorly defined” yellow markings.

03 MAY 2017 | Fairfax County, VA | Ashy Clubtail (male)

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

Coloration is variable among individuals of the same species, so looking at abdominal markings isn’t always a reliable method of identification. In this case, it works beautifully.

Editor’s Note: The word “spearpoint” and the phrase “poorly defined” are descriptors attributed to Dennis Paulson, Dragonflies and Damselflies of the East (Princeton Field Guides). Princeton University Press. Kindle Edition.

Copyright © 2017 Walter Sanford. All rights reserved.

Green-eyed Stream Cruiser

May 12, 2017

Stream Cruiser dragonfly (Didymops transversa) was spotted during a photowalk along a mid-size stream in Fairfax County, Virginia USA. This individual is a male, as indicated by his terminal appendages and indented hind wings.

03 MAY 2017 | Fairfax County, VA | Stream Cruiser (male)

Male: Eyes brown with green highlight above. … Female: Eyes brown. Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 7192, 7194-7195). Princeton University Press. Kindle Edition.

I’ve never seen a green-eyed Stream Cruiser like this one — every one had brown eyes, including both males and females.

Copyright © 2017 Walter Sanford. All rights reserved.

Spine-crowned Clubtail (terminal appendages)

May 10, 2017

A male and female Spine-crowned Clubtail dragonfly (Hylogomphus abbreviatus) were spotted recently in Fairfax County, Virginia USA.

Male

Male dragonflies have three terminal appendages, collectively called “claspers,” that are used to grab and hold female dragonflies during mating: an upper pair of cerci (“superior appendages”); and a lower unpaired epiproct (“inferior appendage”). The epiproct for Spine-crowned Clubtail is essentially a wide plate with two prongs.

03 MAY 2017 | Fairfax County, VA | Spine-crowned Clubtail (male)

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

The hind wings of male clubtail dragonflies are “indented” near the body, as shown in the preceding photograph. In contrast, the hind wings of female clubtails are rounded (shown below). Also notice the right hind wing of the male is slightly malformed.

Female

Female dragonflies have a pair of cerci (superior appendages) that have little or no function. The abdomen of female Spine-crowned Clubtails is noticeably thicker than males of the same species.

03 MAY 2017 | Fairfax County, VA | Spine-crowned Clubtail (female)

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

Copyright © 2017 Walter Sanford. All rights reserved.


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