Archive for the ‘education’ 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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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.

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.

Question Mark

January 23, 2018

A Question Mark butterfly (Polygonia interrogationis) was spotted during a photowalk at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA.

Two field marks can be used to identify this butterfly. First, notice the row of four dark spots on the dorsal side of its forewings (highlighted in an animated GIF by Deb Platt).

Second, notice the silver-white question mark shape on the ventral side of its hind wings (highlighted in an animated GIF by Deb Platt).

Related Resources

Copyright © 2018 Walter Sanford. All rights reserved.

Have you ever wondered…?

January 9, 2018

Have you ever wondered…

The preceding photo shows the “focal plane mark” on my Fujifilm X-T1 digital camera.

The same mark appears on my Canon EOS 5D Mark II DSLR, as shown on p. 16 of the “Instruction Manual.”

Minimum focusing distance versus working distance

The “minimum focusing distance” is the distance from the subject to the focal plane. The “working distance” is the distance from the front of the lens to the subject.

For example, the minimum focusing distance for the Fujinon XF80mm macro lens (shown above) is 246 mm (24.6 cm). The working distance is 98 mm (9.8 cm).

Magnification (or magnification ratio)

True macro lenses have a magnification ratio of at least 1:1, meaning the size of the subject is the same size on the focal plane (digital sensor).

For example, the digital sensor for the Fujifilm X-T1 is 23.6 mm wide by 15.6 mm high. At a magnification ratio of 1:1, a subject that is 15 mm (1.5 cm) long will be 15 mm (1.5 cm) wide on the digital sensor; expressed another way, the subject will fill ~64% of the frame width.

For a prime macro lens, maximum magnification of 1:1 is possible only at the minimum focusing distance; magnification is necessarily lower at longer focusing distances.

Adding an extension tube

Adding a Fujifilm MCEX-11 extension tube reduces the working distance to 89 mm (8.9 cm). It’s interesting to note the minimum focusing distance of 249 mm (24.9 cm) is essentially the same, with or without the extension tube.

The net effect of adding an extension tube is the magnification ratio is increased to a value greater than 1:1, say 1.2:1, so the subject appears slightly larger on the focal plane.

Related Resource: Adding an 11mm extension tube, a blog post by Walter Sanford.

Copyright © 2018 Walter Sanford. All rights reserved.

Visualizing data temporally: Damselflies

December 16, 2017

Google Calendar and Dr. Steve Roble’s excellent datasets for the Commonwealth of Virginia were used to synthesize “CHECKLIST OF THE DRAGONFLIES AND DAMSELFLIES OF VIRGINIA, April 2017 update” into two calendars: Dragonflies (VA Flight Dates); and Damselflies (VA Flight Dates). Dragonflies was presented in my last blog post; Damselflies is presented in this post.

The Damselflies calendar is color-coded Birch, using the Google Calendar default color palette. Individual events on the calendar are also color-coded by family. Here’s the way Damselflies looks using the Chrome Web browser on my Apple iMac desktop computer.

And here’s the way the calendar looks using the free Google Calendar app on my Apple iPad mini 2.

Every event features the following information: common name; scientific name; early-date/late-date; abundance; and habitat.

Regrettably, the color-coding is lost when the calendar is exported as an “.ics” file. That’s the bad news. The good news is the calendar can be edited after it is imported into Google Calendar and it’s easy to edit the entries to color-code them any way you like.

“RGB” was used to color-code the three families of damselflies common to the mid-Atlantic states (USA); the equivalent colors in the Google Calendar default color palette are shown in brackets.

  • R – Family Calopterygidae (Broad-winged Damselflies) [Tomato]
  • B – Family Coenagrionidae (Narrow-winged Damselflies) [Peacock]
  • G – Family Lestidae (Spreadwings) [Basil]

The colors for Narrow-winged Damselflies and Spreadwings were flip-flopped because it just makes sense the Bluets should be color-coded blue!

Tech Tips

Download the “.ics” file from the Virginia Odonata Facebook group. Launch Google Calendar on a desktop computer. Create a new calendar by clicking on the “+” symbol to the left of “Add a friend’s calendar.” (Yeah, yeah — I realize that’s counterintuitive!) Give the calendar a name such as “Test Calendar” and click on the “Create Calendar” button. (You can change the name later.) “Test Calendar” should appear in the list of calendars under “My calendars.”

Mouse-over the name “Test Calendar” and click on the vertical column of three dots, labeled “Options for Test Calendar” then select “Settings and sharing.” In the upper-left sidebar, click on “Import and export”; select the “.ics” file to import and select “Test Calendar” from the drop-down menu labeled “Add to calendar.”

If you decide to color-code individual events like I did, click on an event then click on the pencil icon labeled “Edit event.” Select a color and click the “Save” button, then click the radio button for “All events.” Beware: You can right-click on an individual event and change its color but DON’T GO THERE! That results in an event that doesn’t occur annually using the new color you chose.

Related Resource

Dragonflies & Damselflies of Loudoun County features a flight calendar for dragonflies and damselflies.

Copyright © 2017 Walter Sanford. All rights reserved.

Visualizing data temporally: Dragonflies

December 14, 2017

Regular readers of my blog know I love me some odonates, that is, dragonflies and damselflies. My interest in odonates was rekindled in 2011, along with my interest in photography. Good resources were harder to find in those days. Within the past few years, several datasets of adult flight periods became available publicly. If you are interested in seeing and photographing a particular species of dragonfly, it helps to know when (and where) to look!

In the run-up to the 2017 Dragonfly Society of the Americas Annual Meeting in Staunton, Virginia, 09-11 June 2017, Dr. Steve Roble’s excellent datasets for the Commonwealth of Virginia were posted in the Virginia Odonata Facebook group. (Click on “Files” in the upper-left sidebar.) I used Google Calendar to synthesize “CHECKLIST OF THE DRAGONFLIES AND DAMSELFLIES OF VIRGINIA, April 2017 update” into two calendars: Dragonflies (VA Flight Dates); and Damselflies (VA Flight Dates). Dragonflies is presented in this post; Damselflies will be presented in my next post.

The Google Calendar default color palettes were used to color-code both calendars: Dragonflies is Graphite; and Damselflies is Birch. Individual events on each calendar are also color-coded by family. Here’s the way Dragonflies looks using the Chrome Web browser on my Apple iMac desktop computer.

And here’s the way the calendar looks using the free Google Calendar app on my Apple iPad mini 2.

Every event features the following information: common name; scientific name; early-date/late-date; abundance; and habitat.

Regrettably, the color-coding is lost when the calendar is exported as an “.ics” file. That’s the bad news. The good news is the calendar can be edited after it is imported into Google Calendar and it’s easy to edit the entries to color-code them any way you like.

The colors of the rainbow (ROYGBIV) were used to color-code the seven families of dragonflies; the equivalent colors in the Google Calendar default color palette are shown in brackets.

  • R = Family Aeshnidae (Darners) [Tomato]
  • O = Family Cordulegastridae (Spiketails) [Tangerine]
  • G = Family Corduliidae (Emeralds) [Basil]
  • Y = Family Gomphidae (Clubtails) [Banana]
  • B = Family Libellulidae (Skimmers) [Peacock]
  • I = Family Macromiidae (Cruisers) [Blueberry]
  • V = Family Petaluridae (Petaltails) [Grape]

The colors for Emeralds and Clubtails were flip-flopped because it just makes sense the Emeralds should be color-coded green!

Lessons Learned

As I worked on the calendar, patterns began to emerge that I hadn’t noticed before. For example, it’s clear that the serious odonate hunter needs to hit the ground running as soon as early March. Remember that Dr. Roble’s dataset is for the entire state. You may not see a given species on its early-date, but it could be seen on that date and certainly can’t be seen if you don’t look!

Tech Tips

Download the “.ics” file from the Virginia Odonata Facebook group. Launch Google Calendar on a desktop computer. Create a new calendar by clicking on the “+” symbol to the left of “Add a friend’s calendar.” (Yeah, yeah — I realize that’s counterintuitive!) Give the calendar a name such as “Test Calendar” and click on the “Create Calendar” button. (You can change the name later.) “Test Calendar” should appear in the list of calendars under “My calendars.”

Mouse-over the name “Test Calendar” and click on the vertical column of three dots, labeled “Options for Test Calendar” then select “Settings and sharing.” In the upper-left sidebar, click on “Import and export”; select the “.ics” file to import and select “Test Calendar” from the drop-down menu labeled “Add to calendar.” There are 243 events in the Dragonflies calendar.

If you decide to color-code individual events like I did, click on an event then click on the pencil icon labeled “Edit event.” Select a color and click the “Save” button, then click the radio button for “All events.” Beware: You can right-click on an individual event and change its color but DON’T GO THERE! That results in an event that doesn’t occur annually using the new color you chose.

Related Resource

Kevin Munroe, former manager of Huntley Meadows Park, created an excellent calendar called Dragonflies of Northern Virginia – Flight Periods. This calendar is a valuable resource for hunting dragonflies in Northern Virginia. I think the value of Kevin Munroe’s calendar is enhanced by using it in combination with my visualization of Steve Roble’s dataset.

Copyright © 2017 Walter Sanford. All rights reserved.

“Winter Meadowhawk” dragonflies

December 8, 2017

The season called “winter” is defined two ways: atmospheric scientists, including meteorologists and climatologists, define winter as the three-month period from December to February; astronomers define winter as the time period that begins on the December Solstice (12/21) and ends on the March Equinox (03/21), although the actual dates for these events may vary slightly.

Several Autumn Meadowhawk dragonflies (Sympetrum vicinum) were spotted on the first day of climatological winter at Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA. Therefore I think it is appropriate to call them “Winter Meadowhawks.”

The last two photos show the same male, perching on different surfaces. My guess is he was looking for a good source of thermal energy on a cool, windy day.

The Sun is always low in the sky during winter, even at its maximum altitude. Indirect incoming solar radiation (insolation) is less intense than direct insolation. The last photo shows the male dragonfly perched on a south-facing wooden board that is perpendicular to the surface of the Earth, therefore the solar energy received by the board is more intense than the energy received by the ground. This probably explains why the male moved from the ground to the board.

Enrichment

The last photo was taken on 01 December 2017 at 11:33:50 a.m. EST, as shown by the EXIF information for the image. The altitude of the Sun was 28.9° at 11:30 a.m., meaning a ray of sunlight formed an angle of 28.9° with horizontal surfaces such as the ground. At the same time, a ray of sunlight formed an angle of 61.1° with vertical surfaces such as the wooden board shown in the first and last photos. That’s the beauty of mathematics — some simple geometry shows clearly which surface received more intense insolation. Smart dragonflies!

Related Resource: Sun or Moon Altitude/Azimuth Table, U.S. Naval Observatory.

Copyright © 2017 Walter Sanford. All rights reserved.


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