Posts Tagged ‘exuviae’

Why focus stack macro photos?

April 17, 2018

Why focus stack macro photos? The answer is obvious: The difference between a single macro photo and a focus-stacked composite image is like night and day.

The first example is one of the better photos from a set of 13. It is the same photo that is featured in Hetaerina americana exuvia, my identification guide for American Rubyspot damselfly exuviae.

The last example is a composite image created using all 13 photos in the set.

You may not notice the difference in quality unless you look at the full-size version of both images. When you click on the images they open in a new tab automatically. Toggle back-and-forth between tabs and I think you will agree the composite image is clearly better than the single photo.

The Backstory

An American Rubyspot damselfly (Hetaerina americananymph was collected by Bob Perkins on 06 August 2017 along the New River in Grayson County, Virginia USA. The nymph was reared in captivity, albeit briefly, until it emerged on 09 August 2017.

Copyright © 2018 Walter Sanford. All rights reserved.

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P. lividus prementum

April 11, 2018

The following image shows a composite of six photos of the prementum for an Ashy Clubtail dragonfly (Phanogomphus lividus) exuvia. The composite is one of at least two new images that will be annotated and used to update Phanogomphus lividus exuvia, my identification guide for Ashy Clubtail exuviae.

The Backstory

An Ashy Clubtail dragonfly (Phanogomphus lividusnymph was collected by Bob Perkins. (The date and location where the specimen was collected are unknown.) The nymph was reared in captivity until it emerged on 21 March 2017 and metamorphosed into an adult female. This specimen is the exuvia from the nymph. P. lividus is a member of the Family Gomphidae (Clubtails).

Tech Tips

The following equipment was used to shoot all of the photos for the preceding composite image: Canon EOS 5D Mark II digital camera, in manual mode; Canon MP-E 65mm Macro lens (manual focus only, set for f/8 at ~3x magnification); Canon MT-26EX-RT Macro Twin Lite set for “Master” mode; and Canon 580 EX- and Canon 580EX II Speedlites in “Slave” mode.

Adobe Photoshop CC 2017 was used to create the composite image by “round-tripping” with Apple Aperture.

Copyright © 2018 Walter Sanford. All rights reserved.

Ophiogomphus incurvatus exuvia

March 26, 2018

Disclaimer

Soon after I began creating illustrated identification guides for odonate exuviae, I shared a pointer to Perithemis tenera exuviae on the Northeast Odonata Facebook group. Ed Lam commented on my post. The operative sentence is as follows.

I don’t expect anyone to identify Perithemis tenera larvae from Walter’s blog post but it gives a novice a better sense of what larval identification is all about and that has value. Source Credit: Ed Lam, Northeast Odonata Facebook group.

I disagree with Ed’s comment, although I let it go at the time in deference to Ed’s considerable expertise. I do expect anyone can use my guides to identify the species of odonate featured in each guide. Otherwise, what’s the point of making the guides? After I read Ed’s comment I tweaked the specific blog post and retooled the template that I use for most guides.

All of that being said, in my opinion it would be challenging at best to identify an exuvia from Ophiogomphus incurvatus to the species level using only the dichotomous key in Dragonflies of North America by Needham et al., the best resource currently available — significant sections of the key are unclear and unreliable. In contrast, Bob Perkins and I know the identity of the specimen because Bob observed the species of adult dragonfly that emerged from the exuvia.

For what it’s worth, this blog post features a fairly complete set of annotated photos of an Ophiogomphus incurvatus exuvia. Perhaps the photo set can be used in combination with the dichotomous key in order to make identification easier for others.

The Backstory

An Appalachian Snaketail dragonfly (Ophiogomphus incurvatus) nymph was collected by Bob Perkins. The nymph was reared in captivity until it emerged on 20 March 2017 and metamorphosed into an adult male. This specimen is the exuvia from the nymph. Appalachian Snaketail is a member of the Family Gomphidae (Clubtails).

A two-step process was used to attempt to verify the identity 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), as shown in Photo No. 1, 5, and 6.
  • Antennae are club-like (not thin and thread-like, as in  Aeshnidae larvae), as shown in Photo No. 1.

It’s simple and straightforward to recognize this specimen is a clubtail. Expect a bumpy ride beyond this point!

No. 1 | Ophiogomphus incurvatus | exuvia (face-head)

Step 2. Genus and species

The size of specific antennal segments is a significant marker for identifying some species of Ophiogomphus. In this case, the antennae on the specimen will need to be cleaned in order to count segments and measure their dimensions.

No. 2 | Ophiogomphus incurvatus | exuvia (dorsal)

Lateral spines are present on abdominal segments seven through nine (S7-S9). Dorsal hooks appear to be well developed on segments eight and nine (S8, S9); they resemble “dorsal abdominal processes” on most other abdominal segments.

No. 3 | Ophiogomphus incurvatus | exuvia (dorsal-lateral)

The cerci are approximately three-fourths (3/4) as long as the epiproct and paraprocts.

No. 4 | Ophiogomphus incurvatus | exuvia (anal pyramid)

Photo No. 4 and 5 show ventral views of the exuvia.

No. 5 | Ophiogomphus incurvatus | exuvia (ventral)

The vestigial hamules shown in both photos indicate this individual is a male.

After emergence

The next photograph shows the Appalachian Snaketail dragonfly after emergence from one of Bob Perkins‘ holding tanks. Ophiogomphus incurvatus is 40-43 mm in total length (Paulson, 2011).

Image used with permission from Bob Perkins.

This individual is a male, as indicated by its “indented” hind wings, hamules, and terminal appendages.

Image used with permission from Bob Perkins.

Related Resource

The dichotomous key for Ophiogomphus that appears on pp. 261-262 in Dragonflies of North America, Third Edition by Needham et al. was used to attempt to verify the genus and species of the exuvia. Markers that match this specimen are highlighted in boldface green text. Three boldface green asterisks (***) are used to highlight the thread for identification of O. incurvatus. Disclaimers are highlighted in boldface red text.

p. 261

1. Abdomen without lateral spines or dorsal hooks; antennal segment 4 minute, much narrower than segment 3. [howei]
***1’. Lateral spines present on abdominal segments 6 or 7-9; dorsal hooks usually well developed, if vestigial then antennal segment 4 more than 1/2 as wide as segment 3. [2]

2(1’). Antennal segment 4 more than 1/2 as wide as segment 3 (Fig. 319a); dorsal hooks on abdominal segments 2-9 low and blunt, or vestigial. [3]
***2’. Antennal segment 4 minute, much less than 1/2 as wide as segment 3; dorsal hooks normally prominent, usually hook-like, on at least some of abdominal segments 2-9 (sometimes low in O. carolus). [4]

p. 262

4(2’). Lateral spines on abdominal segments 6-9 (Fig. 323d). [5]
***4’. Lateral spines on abdominal segments 7-9 only. [6]

***6(4’). Dorsal hooks on abdominal segments 2-4 in lateral view usually less than 2/3 as high (measured from lowest point at intersegmental margin) as dorsal length of their respective tergites (along sclerotized, granulated cuticle only), in dorsal view with obtuse apices not extending backward beyond posterior border of tergite (Fig. 322a). [7*]
6’. Dorsal hooks on abdominal segments 2-4 in lateral view 2/3 as high, or more, (measured as above) as dorsal length of their respective tergites, in dorsal view with acute apices extending backward beyond posterior border of tergite (not beyond smooth intersegmental membrane; Fig. 322e). [14*]

***7(6). Antennal segment 3 not more than twice as long as wide. [8**]
7’. Antennal segment 3 is 2.3 to 3.0 times as long as wide. [10**]

***8(7). Antennal segment 3 is 1.7 to 1.8 times as long as wide; dorsal abdominal hooks highest and subequal on segments 2 or 3 to 4 or 5. [incurvatus**]
8’. Antennal segment 3 is 1.8 to 2.0 times as long as wide; dorsal abdominal hooks highest and subequal on segments 2 and 3 (Fig. 322a). [9**]


* Interpretation of this couplet in some individual cases may be ambiguous; if in doubt try both choices.
** Separation based on antennal measurements may be difficult in practice. Careful attention to shape of antennal segments (Fig. 319) should also help.

Tech Tips

The following equipment was used to shoot Photo No. 2, 3, and 5: 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); Canon MT-26EX-RT Macro Twin Lite set for “Master” mode, and Canon 580 EX- and Canon 580EX II Speedlites set for “Slave” mode. Photo No. 1, 4, and 6Canon MP-E 65mm Macro lens (manual focus only, set for 2x magnification) plus the multiple-flash setup.

Adobe Photoshop CC 2017 was used to annotate Photo No. 1-6Photo No. 2, 4, 5, and 6 are focus-stacked composite images.

Bob Perkins’ photos were shot using a Canon EOS Rebel T3i camera body and Canon EF-S 60mm macro lens.

Copyright © 2018 Walter Sanford. All rights reserved.

Before and after

March 6, 2018

A recent blog post entitled Getting Started features photos of four odonate exuviae collected by Michael Powell during a photowalk along the Potomac River in Fairfax County, Virginia USA.

Before

The first photograph is one of several quick-and-dirty shots I took of one of the exuviae, without removing it from the small plastic tub in which it is stored. As you can see, the specimen appears to be in poor condition. Well, appearance can be deceiving, as they say.

No. 1 | Potomac River, Fairfax County, VA | Zygoptera exuvia

After

The last photograph shows the same exuvia after soaking in a bath of soapy water for at least 24 hours. When the specimen was pliable, it could be re-posed and allowed to dry/harden for another 24 hours.

No. 2 | Potomac River, Fairfax County, VA | Zygoptera exuvia

The exuvia is missing a set wing pads and the abdomen is still dented/twisted. That being said, most people would agree the specimen looks much better. More importantly, it’s easier to see the anatomy of the exuvia.

Taxonomic classification

This individual is a member of the Family Coenagrionidae (Narrow-winged Damselflies) as indicated by its keystone-shaped prementum, shown in Photo No. 1. The next challenge is to identify its genus and species.

Copyright © 2018 Walter Sanford. All rights reserved.

Stylurus plagiatus exuvia

March 2, 2018

Michael Powell collected several odonate exuviae during a photowalk along the Potomac River in Fairfax County, Virginia USA, including two damselflies and two dragonflies. The exact date is uncertain, although Mike thinks the exuviae were collected sometime between 19-23 July 2017.

Both dragonfly exuviae are from the Family Gomphidae (Clubtails), as indicated by a flat labium that doesn’t cover the face as well as club-like antennae. The smaller specimen was identified as an Erpetogomphus designatus exuvia; this post describes the decision tree used to identify the larger specimen.

No. 1 | Stylurus plagiatus | exuvia (face-head)

Refer to Photo No. 2, 3, and 4. Notice that abdominal segment nine (S9) is elongated, strongly suggesting this individual is a member of the genus Stylurus.

The dichotomous key for Stylurus larvae that appears on pp. 310-312 in Dragonflies of North America, Third Edition by Needham et al. was used to identify the species of the exuvia. The ninth couplet [9, 9′] is as follows.

9(7’). Length of abdominal segment 9 at least equal to its basal width; lateral spines of abdominal segment 9 at least 1-1/2 times as long as those of segment 8; dorsal hook of segment 9 often large, in southern specimens overhanging segment 10; each labial palp with 3 teeth in addition to end hook; greatest width of prementum at least 4/5 its length. [plagiatus]
9’. Length of abdominal segment 9 less than its basal width; lateral spines of abdominal segment 9 no more than 1-1/2 times as long as those of segment 8; dorsal hook of segment 9 small, sometimes vestigial; labial palp with 2-3 teeth in addition to end hook; greatest width of prementum no more than 3/4 its length. [10]

Abdominal segment nine (S9) is slightly longer than its basal width, as shown in Photo No. 2. The lateral spines of segment nine (S9) are much longer than segment eight (S8).

No. 2 | Stylurus plagiatus | exuvia (dorsal)

Photo No. 3 shows a dorsal view of the distal abdomen. Notice the large dorsal hook of abdominal segment nine (S9) overhangs segment 10 (S10), a key marker for southern specimens of plagiatus. The dorsal hook couldn’t be seen before the exuvia was cleaned.

No. 3 | Stylurus plagiatus | exuvia (dorsal)

The flat labium doesn’t cover the face, as shown in Photo No. 4 and 5.

No. 4 | Stylurus plagiatus | exuvia (ventral)

Photo No. 5 shows a close-up of the prementum. Each labial palp features at least three (3) teeth in addition to the end hook. The greatest width of the prementum is approximately four-fifths (4/5) of its length.

No. 5 | Stylurus plagiatus | exuvia (prementum)

This specimen is confirmed as an exuvia from a Russet-tipped Clubtail dragonfly (Stylurus plagiatus).

The Backstory

Photo No. 6, featured in a recent blog post entitled Getting Started, is focused on abdominal segment nine (S9).

This specimen may need to be cleaned in order to see more clearly some key field markers used for identification.

No. 6 | Potomac River, Fairfax County, VA | odonate exuvia

The specimen was soaked in soapy water for at least 24 hours. A plastic spoon was used to scoop the exuvia from the water bath and transfer it to a dry plastic tray. Then a soft artist’s paintbrush was used to clean the exuvia, with extra attention on abdominal segment nine (S9). Two damselfly exuviae are soaking in the same water bath, shown below. Other useful tools include a magnifying glass and a plastic toothpick.

The odonate exuviae cleaning station at BoG Photo Studio.

The exuvia is pliable after soaking in water for at least 24 hours. After the specimen was cleaned, it was posed and allowed to dry for another day. The handle of a plastic spoon is a good drying rack that makes it easier to pose the legs. The Stylurus plagiatus exuvia is shown in the following photograph. The broken leg resting on the handle of the spoon was attached to the body only by spider web.

Stylurus plagiatus exuvia, posed on the handle of a plastic spoon.

Tech Tips

The following equipment was used to shoot Photo No. 1, 2 and 4: 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 LitePhoto No. 3 and 5: Canon EOS 5D Mark II digital camera, in manual mode; Canon MP-E 65mm Macro lens (manual focus only, set for 2x magnification); 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.

A Panasonic Lumix DMC-FZ150 superzoom bridge camera was used to take photos of the odonate exuviae cleaning station.

Adobe Photoshop CC 2017 was used to annotate selected images.

Related Resources

Copyright © 2018 Walter Sanford. All rights reserved.

Getting started

February 26, 2018

Michael Powell, a good friend and fellow Northern Virginian, collected several odonate exuviae during a photowalk along the Potomac River in Fairfax County, Virginia USA.

The four exuviae that Mike collected are stored in one of those empty containers of Philadelphia cream cheese spread that I endorsed in a recent blog post. I shot several quick-and-dirty photographs of the exuviae, without removing them from the small plastic tub. Usually I wouldn’t publish photos of this quality. The photos are like a sketch pad that will be used to make a tentative plan for photographing the specimens and attempting to identify them to the genus and species level, if possible.

Spoiler Alert: If you can identify any of the exuviae featured in this post, then PLEASE DON’T TELL ME! I enjoy the challenge of solving the mystery of their identity. Thank you!

Dragonfly exuviae

Mike collected two dragonfly exuviae that are from the Family Gomphidae (Clubtails), as indicated by a flat labium that doesn’t cover the face as well as club-like antennae.

My working theory is the first specimen might be an exuvia from an Eastern Ringtail dragonfly (Erpetogomphus designatus).

Potomac River, Fairfax County, VA | odonate exuvia

Post Update: The identity of the first specimen is confirmed as an Erpetogomphus designatus exuvia.

The next exuvia appears to be a member of the genus Stylurus, possibly plagiatus (Russet-tipped Clubtail).

Potomac River, Fairfax County, VA | odonate exuvia

The preceding photo was focused on the head; the following photo was focused on abdominal segment nine (S9). This specimen may need to be cleaned in order to see more clearly some key field markers used for identification.

Potomac River, Fairfax County, VA | odonate exuvia

Post Update: The identity of the first specimen is confirmed as a Stylurus plagiatus exuvia.

Damselfly exuviae

It is relatively easy to identify damselflies (Suborder Zygoptera) to the family level based upon the shape of the prementum. Both damselfly exuviae that Mike collected are members of the Family Coenagrionidae (Narrow-winged Damselflies).

It is more challenging to identify damselfly specimens to the genus/species level. In this case, possible genera include Argia (Dancers), Enallagma (American Bluets), and Ischnura (Forktails).

Potomac River, Fairfax County, VA | odonate exuvia

The last damselfly exuvia is smaller than the first. It will need to be soaked in soapy water for at least 24 hours in order to make the specimen pliable so it can be re-posed before it is photographed.

Potomac River, Fairfax County, VA | odonate exuvia

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.

Epitheca cynosura exuvia

April 26, 2017

On 13 April 2017, a late-stage emergent teneral female Common Baskettail dragonfly (Epitheca cynosura) was observed at Painted Turtle Pond during a photowalk around Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA.

Several dragonfly exuviae were collected near the same location as the emergent teneral female. All of the exuviae look identical, although there is some variation in size. A two-step process was used to verify the genus and species for one of the larger exuvia.

  • Determine the family.
  • Determine the genus and species.

This specimen is approximately 22 mm (~0.87 in) in length.

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 Corduliidae (Emeralds).

  • The specimen has a mask-like labium that covers the face, characteristic of four families: Cordulegastridae (Spiketails); Corduliidae (Emeralds); Libellulidae (Skimmers); and Macromiidae (Cruisers).
  • There is no horn on top of the face-head, characteristic of Macromiidae, so it’s not a cruiser.
  • Cordulegastridae has jagged crenulations on its labium, so it’s not a spiketail. The crenulations for Corduliidae and Libellulidae look similar.
  • Look at the anal pyramid to differentiate Corduliidae and Libellulidae [See Photo No. 7.]: It’s probably Corduliidae if the cerci are at least half as long as the paraprocts. [Editor’s Note: It’s probably Libellulidae if the cerci are less than half the length of the paraprocts.]

In summary, the exuvia has a mask-like labium with relatively smooth crenulations, no horn on its face-head, and the cerci are more than half as long as the paraprocts, confirming that the specimen is a member of Family Corduliidae (Emeralds).

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

Notice that dorsal hooks are present and well developed on most abdominal segments.

No. 4 | Common Baskettail (Epitheca cynosura) | exuvia (dorso-lateral)

A lateral view of the exuvia provides a good look at the labium, also known as 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.

The white filaments that extend from the split in the thorax (as shown in Photo No. 1-7) are breathing tubes, artifacts of the unique respiratory system of dragonfly nymphs.

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

A closer view of the head shows two “bumps” that may be a pair of tubercles.

Step 2. Genus and species

Characters from Identification Keys to Northeastern Anisoptera Larvae, dichotomous keys compiled by Ken Soltesz, were used to identify the genus and species for the exuvia. Although palpal/mental setae were not examined, all other characters match Epitheca cynosura.

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

Alternate Key to the Genera of the Family Corduliidae, p. 29.

Key to the species of the genus (subgenus) Tetragoneuria, p. 32.

No. 7 | Common Baskettail (Epitheca cynosura) | exuvia (anal pyramid)

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

The last photo shows a ventral view of the exuvia. The vestigial hamuli located between abdominal segments two and three (S2-3) strongly suggests this individual is a male, therefore this specimen probably is not the same exuvia from which the teneral female emerged.

(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 tethered to the camera by a coiled six-foot Vello Off-Camera TTL Flash Cord for Canon Cameras, off-camera, in manual mode; the Canon flash optically triggered a small Nissin i40 external flash (in SF mode) used for backlight; and a Sunpak LED-160 Video Light with a white translucent plastic filter used for side light.

Adobe Photoshop CC 2017 was used to annotate selected images.

Related Resources:

Editor’s Note: Sincere thanks to Sue Gregoire, Kestrel Haven Migration Observatory, for verifying my tentative identification, and for sharing some good odonate nymph knowledge regarding vestigial hamuli!

Copyright © 2017 Walter Sanford. All rights reserved.

Late-stage emergent baskettail dragonfly

April 18, 2017

Common Baskettail dragonfly (Epitheca cynosura) was spotted at Painted Turtle Pond during a photowalk around Occoquan Bay National Wildlife Refuge (OBNWR), Prince William County, Virginia USA. This individual is a late-stage emergent teneral female.

I photographed the process of emergence from the first sighting to the time when the teneral dragonfly flew away: I shot 23 photos in approximately 16 minutes; time is compressed by showcasing six (6) select photos taken at major milestones during the event.

The following photo is the first image from a time-series documenting the emergence of the teneral female. Elapsed time is expressed in hh:mm:ss format, e.g., 00:00:00 is the time when I spotted the emergent teneral female, and 00:16:08 is the total elapsed time.

13 APR 2016 | 11:38:41 am EDT | Elapsed time: 00:00:00

Notice the drop of fluid at the tip of the abdomen. Emerging dragonflies pump fluid into their wings, causing the wings to expand. Next, the same fluid is withdrawn from the wings and used to expand the abdomen. Excess fluid is expelled afterward.

13 APR 2016 | 11:40:48 am EDT | Elapsed time: 00:02:07

The next photo shows the first time the wings opened.

13 APR 2016 | 11:48:55 am EDT | Elapsed time: 00:10:14

Then the wings closed again and remained closed for a while.

13 APR 2016 | 11:51:02 am EDT | Elapsed time: 00:12:21

The wings reopened a few minutes later. Notice that several wings are malformed slightly.

13 APR 2016 | 11:54:14 am EDT | Elapsed time: 00:15:33

Finally, the wings open up, and very soon the teneral adult flies away. Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 468). Princeton University Press. Kindle Edition.

The teneral female dragonfly flew away immediately after the last photo in the time-series.

13 APR 2016 | 11:54:46 am EDT | Elapsed time: 00:16:08

This individual is a female, as indicated by her cerci (superior appendages) and thick abdomen. Common Baskettail females have shorter cerci and a thicker abdomen than males of the same species.

Exuviae (in situ)

Several dragonfly exuviae were spotted at Painted Turtle Pond. The exuviae were identified using a dichotomous key for dragonfly larvae; they are cast skins from Common Baskettail.

13 APR 2017 | OBNWR | Common Baskettail (exuvia)

These exuviae are not the one from which the teneral female featured in this post emerged.

13 APR 2017 | OBNWR | Common Baskettail (exuvia)

Copyright © 2017 Walter Sanford. All rights reserved.

Perithemis tenera exuviae

December 6, 2016

Several unknown dragonfly exuviae were collected on 07 July 2016 from the Potomac River, Fairfax County, Virginia USA; two of the specimens are featured in this post. A two-step process was used to identify the genus and species of the specimens.

Family

First, determine the family of the specimens. For reference, watch the excellent Vimeo video, Identifying dragonfly larva to family (8:06).

The exuviae have a mask-like labium (not flat) with smooth crenulations, indicating these individuals are members of Family Libellulidae (Skimmers).

Genus and species

A dichotomous key was used to tentatively identify the exuviae as Eastern Amberwing dragonfly (Perithemis tenera), as indicated by the following morphological characteristics.

  • The cerci (sing. cercus) are slightly less than half the length of the paraprocts.
  • Dorsal hooks are clearly visible on abdominal segments four through nine (S4-9), plus a “nub” that is visible on segment three (S3).
  • Lateral spines are clearly visible on abdominal segments eight and nine (S8-9).

These specimens are the first odonate exuviae that I was able to identify to the species level. Sincere thanks to Sue Gregoire, Kestrel Haven Migration Observatory, for verifying my preliminary observations and tentative identification.

No. 1

Each specimen is approximately 1.4 cm (~0.6″) in length and approximately 0.6 cm (~0.2″) in maximum width. In Photo No. 1, the specimen shown on the left is an emergent nymph that was stuck in its exuvia.

A pair of Eastern Amberwing dragonfly (Perithemis tenera) exuviae collected from the Potomac River, Dyke Marsh Wildlife Preserve, Fairfax County, Virginia USA.

No. 1 | Eastern Amberwing (Perithemis tenera) | exuviae (lateral, dorsal)

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

The white filaments that extend from the split in the thorax (as shown in Photo No. 1-3) are breathing tubes, artifacts of the unique respiratory system of dragonfly nymphs.

No. 2

An Eastern Amberwing dragonfly (Perithemis tenera) exuvia collected from the Potomac River, Dyke Marsh Wildlife Preserve, Fairfax County, Virginia USA.

No. 2 | Eastern Amberwing (Perithemis tenera) | exuviae (dorsal)

No. 3

The eyes are relatively small and widely separated. Notice the mask-like labium (sometimes referred to as “spoon-shaped”) with smooth crenulations along the margins between two lateral lobes.

An Eastern Amberwing dragonfly (Perithemis tenera) exuvia collected from the Potomac River, Dyke Marsh Wildlife Preserve, Fairfax County, Virginia USA.

No. 3 | Eastern Amberwing (Perithemis tenera) | exuviae (head-on)

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

No. 4

One of the keys to identifying skimmer dragonflies to the species level is to carefully examine the anal pyramid (see S10, shown below), including the cerci (sing. cercus) and paraprocts. Notice the cerci are slightly less than half the length of the paraprocts.

An Eastern Amberwing dragonfly (Perithemis tenera) exuvia collected from the Potomac River, Dyke Marsh Wildlife Preserve, Fairfax County, Virginia USA.

No. 4 | Eastern Amberwing (Perithemis tenera) | exuviae (anal pyramid)

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

Tech Tips:

The following equipment was used to shoot the preceding photographs:

Adobe Photoshop CC 2017 was used to annotate selected images.

Related Resources:

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

Assuming the convention of labeling the two branches of each dichotomy as “a” and “b”, e.g. 1a, 1b, etc., a list of branches in the decision tree that I used to identify the species of the dragonfly exuviae is as follows: 1b; 4b; 5a; 6a BINGO!

In long form, the decision tree is as follows:

p. 36, Key to the Genera of the Family Libellulidae
1b – Eyes lower, more broadly rounded and more lateral in position; abdomen usually ending more bluntly. [Go to] 4
4b – These appendages [inferior abdominal appendages (paraprocts)] straight or nearly so. [Go to] 5
5a – Dorsal hooks on some abdominal segments. [Go to] 6
6a – Dorsal hook on 9. Perithemis (One species, Perithemis tenera.) BINGO!

Copyright © 2016 Walter Sanford. All rights reserved.


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