Archive for the ‘Aperture’ Category

Miraculous metamorphosis

February 22, 2018

It’s hard to believe an odonate larva that looked like this…

…transformed into the adult dragonfly shown below.

Image used with permission from Bob Perkins.

The Backstory

Bob Perkins, a good friend and fellow Virginian, has been collecting and rearing odonate larvae since 01 January 2017. Bob’s success rate is extraordinarily high, meaning most of the larvae he collects live to emerge as adults.

Bob collected an unknown species of clubtail larva in February 2017 from a stream located in either Carroll- or Grayson County, Virginia USA. The larva emerged from one of Bob’s holding tanks on 13 March 2017 and metamorphosed into an adult female Sable Clubtail dragonfly (Stenogomphurus rogersi).

Amateur- and professional scientists collect and rear odonate larvae in order to see what adult species emerge. Then it is possible to reverse-engineer the morphological characters that enable identification of specific species of larvae. An upcoming blog post will feature information about how to identify Sable Clubtail larvae.

Tech Tips

The first image is a composite of nine (9) photos taken using the following equipment: Canon EOS 5D Mark II digital camera, in manual mode; Canon MP-E 65mm Macro lens (manual focus only, set for 3x magnification); and Canon MT-26EX-RT Macro Twin Lite.

Adobe Photoshop CC 2017 was used to focus stack the photos and post-process the final output.

The second image was taken by Bob Perkins, soon after emergence, using a Canon EOS Rebel T3i camera body and Canon EF-S 60mm macro lens.

Copyright © 2018 Walter Sanford. All rights reserved.

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American Lady butterfly

February 20, 2018

An American Lady butterfly (Vanessa virginiensis) was spotted during a photowalk at Meadowood Recreation Area, Fairfax County, Virginia USA.

This butterfly looks similar to several species with which I’m familiar but isn’t a perfect match, so I consulted the experts on the BugGuide Facebook group. Sincere thanks to Matt Pelikan, Jack Blackford, and Ken Childs for help in identifying the butterfly.

Copyright © 2018 Walter Sanford. All rights reserved.

What is it?

February 18, 2018

It’s time for another exciting edition of “What is it?” Well, what is shown in the following photograph?

What is shown in this photograph?

If you were thinking “empty containers of Philadelphia cream cheese spread,” then you’re only half right.

These small plastic tubs can be repurposed as storage containers for odonate exuviae, such as the Sable Clubtail dragonfly (Stenogomphurus rogersi) exuvia shown below. (Oops, I just noticed it’s time to update the label on the container!)

Storage container for a Sable Clubtail dragonfly (exuvia).

The containers are ideal in many ways. They’re not too big and not too small. The tubs can be “nested” so they don’t take up much space when you’re in the field. For long-term storage, the closed containers can be stacked neatly inside a larger box such as a Rubbermaid Keeper. And the tubs can be used to soak specimens in soapy water in order to clean- and/or re-pose exuviae when they’re pliable.

Finally, think about all the tasty toasted bagels and cream cheese that you get to eat in order to build a collection of specimen containers — that’s what I call a win-win situation!

Copyright © 2018 Walter Sanford. All rights reserved.

Post update: Cordulegastridae exuvia

February 16, 2018

In a recent blog post entitled Cordulegastridae exuvia, I was able to identify the specimen to the family level. Since then, I was able to identify the genus and species.

The dichotomous key for Cordulegastridae larvae that appears on p. 330 in Dragonflies of North America, Third Edition by Needham et al. was used to identify the exuvia.

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

The first couplet [1, 1′] is as follows.

1. No lateral spines on abdominal segments 8-9; western [2]
1’. Lateral spines present on segments 8-9; eastern [3]

No. 1 | Cordulegaster sp. | exuvia (ventral)

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

Since the preceding annotated image shows lateral spines on abdominal segments eight and nine (S8, S9), proceed to the third couplet [3, 3′].

3(1’). Palpal setae 4; usually 5 large and 5 small premental setae present; some setae on margin of frontal shelf spatulate (Fig. 391e) [erronea]
3’. Palpal setae 5-7; 5-9 large and 3-5 small premental setae present; all setae on frontal shelf slender, not spatulate (Fig. 391f) [4]

No. 2 | Cordulegaster sp. | exuvia (inner prementum)

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

The preceding annotated image shows the inner side of the prementum. Four (4) palpal setae are present, plus five (5) large- and five (5) small premental setae. The premental setae on the lower-right side of the prementum seem to be more intact than the ones on the upper-left: the large premental setae are labeled using white numerals; the small premental setae are labeled using red numerals.

The setae on the frontal shelf are mostly missing, as shown below. It’s possible they were broken off either when the larva burrowed in stream sediment (personal correspondence, Sue Gregoire) or when I cleaned the specimen.

No. 3 | Cordulegaster sp. | exuvia (frontal shelf)

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

Genus and species

The number of palpal setae strongly indicates the specimen is an exuvia from a Tiger Spiketail dragonfly (Cordulegaster erronea). Further, the rudimentary ovipositor shown in Photo No. 1 indicates this individual is a female.

The face behind the mask

Do you remember the way the female exuvia looked with its mask-like labium in place? In my opinion, she looked exotically beautiful!

No. 4 | Cordulegaster sp. | exuvia (face-head)

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

Well, that was then and this now. The following photo shows the face and mouth of the exuvia after the face mask was pulled away from the face in order to count the setae on the inner side of the prementum. Look closely at the full-size version of the photo. Yikes, that’s the stuff of nightmares!

No. 5 | Cordulegaster sp. | exuvia (face and mouth)

Tech Tips

The following equipment was used to shoot macro Photo No. 2, 3 and 5: Canon EOS 5D Mark II digital camera, in manual mode; Canon MP-E 65mm Macro lens (set for 2x); and Canon MT-26EX-RT Macro Twin Lite. A Sunpak LED-160 Video Light (with a white translucent plastic filter) was used for some photos.

The following equipment was used to shoot macro Photo No. 1 and 4Fujifilm X-T1 digital camera; Fujifilm MCEX-11 extension tube; and Fujinon XF80mm macro lens. An off-camera Fujifilm EF-X500 external flash unit and Sunpak LED-160 Video Light (with a white translucent plastic filter) were used for Photo No. 4. A Raynox DCR-250 close-up filter and Canon MT-26EX-RT Macro Twin Lite was used for Photo No. 1.

Adobe Photoshop CC 2017 was used to annotate selected images.

Related Resource: Cordulegastridae exuvia, a blog post by Walter Sanford featuring an exuvia collected by Mike Boatwright.

Copyright © 2018 Walter Sanford. All rights reserved.

Tachopteryx thoreyi exuvia

February 14, 2018

A Gray Petaltail dragonfly (Tachopteryx thoreyi) exuvia was collected on 28 May 2017 by Mike Boatwright in Amherst County, Virginia USA. Gray Petaltail is a member of the Family Petaluridae (Petaltails).

The exuvia has a flat labium, similar to members of the Family Aeshnidae (Darners) and Family Gomphidae (Clubtails). Its seven-segmented antennae are thick and club-like, similar to Clubtail dragonflies.

No. 1 | Gray Petaltail (Tachopteryx thoreyi) | exuvia (face-head)

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

The specimen is ~3.5 cm long and  ~1 cm wide. The wing pads extend to the end of abdominal segment five (S5), as shown in Photo No. 2. The exuvia features two rows of dorsal hooks down its back.

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

Photo No. 3 shows a ventral view of the exuvia. Notice the “rudimentary ovipositor” located on abdominal segment nine (S9). An ovipositor is used for egg-laying by all adult damselflies and some species of adult dragonflies: females have this feature; males do not. Therefore, this individual is a female Gray Petaltail.

(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; Kenko 20mm macro automatic extension tube; Canon EF100mm f/2.8L Macro lens (set for manual focus); and Canon MT-26EX-RT Macro Twin Lite. A Sunpak LED-160 Video Light (with a white translucent plastic filter) was used for some photos.

Adobe Photoshop CC 2017 was used to annotate selected images.

The Backstory

Mike Boatwright has steadfastly resisted my best efforts to lure him to the dark side of odonate exuviae collection and identification. As a concession to me, Mike kindly agreed to look-out for exuviae in unusual habitats. As it turns out, the first exuvia Mike collected for me is a prized specimen. Perhaps I should have titled this post “Mike strikes gold in Virginia!”

Image used with permission from Mike Boatwright.

“Beginner’s luck?” Nope. I know from firsthand experience Mike Boatwright is an extraordinarily keen-eyed odonate hunter. Way to go, Mike!

Related Resource

The dichotomous key for Petaluridae larvae that appears on p. 320 in Dragonflies of North America, Third Edition by Needham et al. is as follows.

1. Antennae 6-segmented, 3rd and 5th segments longer than wide (Fig. 381); cerci each more than 1/2 as long as epiproct; lateral margins of abdominal segments 3-9 not expanded, lateral spines inconspicuous; western [Tanypteryx (p. 322)]
1’. Antennae 7-segmented, 3rd and 5th segments not longer than wide (Fig. 379); cerci each less than 1/2 as long as epiproct; lateral margins of abdominal segments 3-9 expanded, lateral spines conspicuous; eastern [Tachopteryx (p. 321)]

Copyright © 2018 Walter Sanford. All rights reserved.

How to calculate magnification

February 12, 2018

By definition, a true macro photo is one with a magnification of at least 1/1, that is, one unit in the real world is equal to at least one of the same units on the camera sensor. Magnification can be calculated using the following formula.

actual size of image / size of camera sensor = magnification

Both measurements must be expressed in the same units in order for the units to cancel during division.

For example, let’s look at the following “full-size” image of a Corduligastridae exuvia. “Full-size” means the image is uncropped (4896 x 3264 pixels).

The photograph shown above was taken using a Fujifilm X-T1 digital camera, Fujifilm MCEX-11 extension tube, and Fujinon XF80mm macro lens. The specifications for the macro lens lists the maximum magnification as 1x. Question is, how much is the magnification increased by adding the 11 mm extension tube?

The dragonfly exuvia is approximately 35 mm in length (3451 pixels). The following proportion can be used to solve for the length of the entire image, in millimeters (mm).

x mm / 35 mm = 4896 pixels / 3451 pixels

x = 49.65 mm, or ~50 mm. In other words, if a metric ruler were placed in the scene then 50mm of the ruler would be shown in the preceding photograph.

The X-T1 features an APS-C sensor (23.6 mm x 15.6 mm). Calculate the magnification using the following formula.

50 mm / 23.6 mm = 2.11x or ~2.0x

The subject is actually ~2.0x larger than life size on the camera sensor.

1.19x is listed as the theoretical maximum magnification using an MCEX-11 extension tube mounted on the 80mm macro lens. If we round the spec’d magnification to ~1.2x, then it’s clear that the actual magnification of ~2.0x is slightly greater than advertised.

Related Resource: Photomacrography using Bellows and Extensions (13:11), by Gale Spring, Adjunct Associate Professor of Scientific Photography at RMIT University in Melbourne, Australia.

Copyright © 2018 Walter Sanford. All rights reserved.

Long-jawed Orb Weavers

February 10, 2018

Long-jawed Orb Weavers (Family Tetragnathidae) are commonly spotted at Mulligan Pond, Jackson Miles Abbott Wetland Refuge, Fairfax County, Virginia USA.

02 AUG 2017 | JMAWR | Long-jawed Orb Weaver

The common name is due to the extended length of the chelicerae (jaws) compared to those of other orb weavers (Araneidae). Source Credit: Family Tetragnathidae – Long-jawed Orb Weavers, BugGuide.

05 SEP 2017 | JMAWR | Long-jawed Orb Weaver

Related Resources

Copyright © 2018 Walter Sanford. All rights reserved.

Predator and prey

February 8, 2018

A Black and Yellow Argiope (Argiope aurantia) was spotted during a photowalk along Deephole Point Road at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA. A female Common Whitetail dragonfly (Plathemis lydia) is trapped in the spider web.

“Eat or be eaten” is perhaps the most fundamental law of nature. Predator-prey relationships can change suddenly: one minute a predator, such as a dragonfly, is hunting for its next meal; next minute the dragonfly becomes the prey and is a meal for another predator, such as a spider, elsewhere in the food web.

Copyright © 2018 Walter Sanford. All rights reserved.

Cordulegastridae exuvia

February 6, 2018

My good friend Mike Boatwright, a fellow Virginian and extraordinarily good odonate hunter, collected an exuvia on 22 June 2017 in Amherst County, Virginia USA. Mike sent the exuvia to me for identification. This specimen is a member of the Family Cordulegastridae (Spiketails).

Photo No. 1 enabled me to see all of the critical field markers required to make an identification to the family level for this specimen. Here’s the decision tree I used to identify the exuvia as a spiketail dragonfly, based upon the excellent Vimeo video, Identifying dragonfly larva to family (8:06).

  • The specimen has a mask-like labium.
  • The margins of the labium have “deeply jagged, irregular teeth.”

Of the four families of dragonflies that feature a mask-like labium, the crenulations on the face of Corduligastridae are unmistakeable!

No. 1 | Cordulegaster sp. | exuvia (face-head)

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

The specimen is ~3.5 cm long (~1.4 in) and ~8 mm wide (0.3 in) at its widest. Notice the dorsal side of the exuvia is covered by sandy grit. The specimen will need to be cleaned in order to get a clearer view of the frontal shelf.

No. 2 | Cordulegaster sp. | exuvia (dorsal)

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

Photo No. 3 shows a ventral view of the exuvia.

No. 3 | Cordulegaster sp. | exuvia (ventral)

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

Photo No. 4 shows a closer view of the “rudimentary ovipositor,” located on abdominal segment nine (S9). An ovipositor is used for egg-laying by all adult damselflies and some species of adult dragonflies: females have this feature; males do not. Therefore, this individual is a female spiketail.

No. 4 | Cordulegaster sp. | exuvia (ventral, rudimentary ovipositor)

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

Photo No. 5 shows a closer view of the mentum, a two-segment hinged “jaw” that is used to grab food: the prementum is the segment of the labium closer to the mouth; the postmentum is the segment closer to the base of the head. Only the prementum can be seen in the following photo.

No. 5 | Cordulegaster sp. | exuvia (ventral, prementum)

Determining the genus and species

Although it’s easy to identify Cordulegastridae exuvia to the family level, it’s more challenging to identify a specimen to the species level. First, the exuvia must be cleaned in order to show the small hairs and brown dots on the frontal shelf. Second, the labium must be pulled forward to show the inside of the face mask in order to count palpal- and premental setae.

Tech Tips

The following equipment was used to shoot all of the macro photographs featured in this post: Fujifilm X-T1 digital camera; Fujifilm MCEX-11 extension tube; and Fujinon XF80mm macro lens. An off-camera Fujifilm EF-X500 external flash unit and Sunpak LED-160 Video Light (with a white translucent plastic filter) were used for Photo No. 1-3 and 5. A Raynox DCR-250 close-up filter and Canon MT-26EX-RT Macro Twin Lite was used for Photo No. 4.

Adobe Photoshop CC 2017 was used to annotate selected images.

Related Resources

Copyright © 2018 Walter Sanford. All rights reserved.

Male Blue-faced Meadowhawk dragonflies

February 4, 2018

On the same day that I saw a male Blue-faced Meadowhawk dragonfly (Sympetrum ambiguum) with an eye injury, one or more other males were photographed at the same location in Huntley Meadows Park, Fairfax County, Virginia USA.

22 OCT 2017 | HMP | Blue-faced Meadowhawk (male)

Please look at the full-size version of each photo in order to fully appreciate these handsome little devils!

22 OCT 2017 | HMP | Blue-faced Meadowhawk (male)

22 OCT 2017 | HMP | Blue-faced Meadowhawk (male)

22 OCT 2017 | HMP | Blue-faced Meadowhawk (male)

22 OCT 2017 | HMP | Blue-faced Meadowhawk (male)

Copyright © 2018 Walter Sanford. All rights reserved.


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