Posts Tagged ‘dorsal hooks’

Uhler’s Sundragon dragonfly exuvia

June 1, 2021

Michael Powell spotted a small odonate exuvia clinging to the base of one of two concrete abutments for a man-made dam located along a mid-size stream at an undisclosed location in Prince William County, Virginia USA.

I collected the exuvia in order to examine it more closely in my home laboratory/photography studio. Michael photographed the specimen in my hand immediately after I removed it from the abutment, as shown in the following photo.

Photo used with written permission from Michael Powell.

The first photo shows a face-head view of the exuvia.

13 APR 2021 | Prince William County, VA | Uhler’s Sundragon (exuvia)

The next two photos, showing a dorsal-lateral view of the specimen, confirm the exuvia is from a Uhler’s Sundragon dragonfly (Helocordulia uhleri).

Notice the dorsal hooks on abdominal segments seven through nine (S7-9). This distinctive character confirms the identity of the specimen as H. uhleri.

13 APR 2021 | Prince William County, VA | Uhler’s Sundragon (exuvia)

Another photo taken from the same view point, exposed and edited for more contrast, shows the three dorsal hooks a little more clearly than the preceding photo.

13 APR 2021 | Prince William County, VA | Uhler’s Sundragon (exuvia)

Knowing when good is good enough

A dear friend sent an article to me years ago entitled “Knowing when good is good enough.” I think she was trying to tell me something.

I tend to be a perfectionist. For example, I’m a man on a mission to take the best possible macro photographs of odonate larvae and exuviae given the limitations of my photography gear and small home studio.

Sometimes perfection is a road block that prevents me from shooting and posting photos that are more than serviceable for my purposes, in this case, informal instruction.

I did a quick Google search for the article from my friend. No luck, but I found one that’s close enough — you might even say one that’s good enough — for a little self-help.

None of the photographs in this blog post are perfect — not even close! But I published them anyway. Baby steps, Bob.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Uhler’s Sundragon dragonfly (emergent female)

April 27, 2021

Uhler’s Sundragon (Helocordulia uhleri) was spotted during a recent photowalk with Michael Powell along a mid-size stream at an undisclosed location in Prince William County, Virginia USA.

The dragonfly was perched on the exuvia from which it emerged; its cast skin was still clinging to a grass stem approximately six inches (6″) above the ground. The patch of grass was located two-to-three feet from the shoreline, where the stream current was slow-to-moderate. The stream bed was sandy and gently sloped near the site on land where the dragonfly larva stopped to eclose.

This individual is an emergent female, as indicated by her teneral appearance, rounded hind wings, terminal appendages, and subgenital plate.

13 APR 2021 | Prince William County, VA | Uhler’s Sundragon (emergent female)

The subgenital plate is located on the ventral side of the abdomen beneath segment eight.

Underneath Segment 8 there is either an ovipositor or a subgenital plate, depending upon the species [of dragonfly]. Both structures are for laying eggs and extend over Segment 9 and possibly beyond. Source Credit: Dragonflies of the North Woods, by Kurt Mead.

Remember that “Segment 8 and 9” refers to abdominal segments eight and nine (of 10), numbered from front to back.

13 APR 2021 | Prince William County, VA | Uhler’s Sundragon (emergent female)

The following graphic from Dragonflies and Damselflies of the East by Dennis Paulson shows the shape of the subgenital plate on our emergent female matches Uhler’s perfectly.

Graphic used with written permission from Dennis Paulson.

True Detective

Generally speaking, teneral odonates are more challenging to identify than most mature adult dragonflies and damselflies. Full disclosure: Neither Mike nor I were certain of the identity of the emergent female when we were shooting photographs in the field. “Shoot first and ask questions later” is one of my mantras for wildlife photography.

The most reliable way to identify odonate larvae to the species level is to rear them to maturity and emergence, that is, unless you’re fortunate to find a larva emerging in the field. Since an exuvia is essentially a nearly perfect shell of the last instar, it can be used to identify other specimens of the same species by pattern matching.

In this case, I used the exuvia to reverse-engineer the identity of the teneral dragonfly. Look closely at a lateral view of the exuvia, as shown in the following photo taken by Mike Powell. Notice there are dorsal hooks on abdominal segments seven, eight, and nine (S7-9). This distinctive field mark confirms the identity of the species as H. uhleri.

Photo used with written permission from Michael Powell.

Also notice Mike’s photo shows a clear view of the emergent female’s terminal appendages, as well as the subgenital plate on the underside of her abdomen.

How it all began, and ended.

The sky was almost completely overcast and it was cool and windy when I spotted the emergent female. Mike Powell and I observed the dragonfly for quite a while and there was little noticeable progress. According to Michael Boatwright, founder and administrator of the Virginia Odonata Facebook group, the process of emergence can take longer when the air temperature is cooler.

When the sky began clearing, Mike Powell and I decided to go to a nearby place where he had seen adult Uhler’s recently. Later the same day, we returned to the site of the emergent female; she was gone, so I collected the exuvia. I plan to publish a photo set of the exuvia in an upcoming blog post. To be continued.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Post update: Tachopteryx thoreyi exuvia

March 26, 2021

I just updated an older blog post in order to correct a label for an anatomical structure that was mislabeled, plus I added some new information.

The updated annotated image is shown below.

No. 2 | Gray Petaltail (Tachopteryx thoreyi) | exuvia (dorsal)

While I was editing the photo, I noticed something I hadn’t seen before — a large dorsal hook of abdominal segment nine (S9) that overhangs segment 10 (S10). This time I’m fairly sure the structure is correctly called a dorsal hook.

Related Resource: Tachopteryx thoreyi exuvia, an updated version of a blog post by Walter Sanford.

Copyright © 2021 Walter Sanford. All rights reserved.

Dromogomphus spinosus exuvia (dorsal view)

February 19, 2021

Gomphidae (Clubtails) is the second largest family of dragonflies, behind Libellulidae (Skimmers). Many types of clubtail larvae (nymphs)/exuviae look similar, adding to the challenge of identifying some specimens to the genus and species level.

This specimen has a flat labium that doesn’t cover the face (not mask-like), indicating it’s either Aeshnidae (Darners) or Gomphidae; the shape of the body suggets Gomphidae. Several more field marks can be used to identify this specimen as a Black-shouldered Spinyleg (Dromogomphus spinosus) exuvia.

16 FEB 2021 | BoG Photo Studio | D. spinosus exuvia (dorsal)

The specimen is approximately 3.3 cm (~1.3 in) long, measured from head to tail. Notice the mid-dorsal hooks/spines located along the abdomen of the body.

At first I thought the exuvia might be a species from the genus Stylurus, based upon the mid-dorsal spine on abdominal segment nine (S9). After careful examination of two excellent photo-illustrated PowerPoint presentations by Kevin Hemeon at NymphFest 2016 (see Related Resources, below), I noticed none of the species in the genus Stylurus have dorsal hooks. That’s when I realized the specimen must be D. spinosus. Eureka! Source Credit: Dromogomphus spinosus exuvia – a blog post published on 28 June 2019 by Walter Sanford.

Related Resources

The following PowerPoint presentations by Kevin Hemeon are available in the “Files” section of the Northeast Odonata Facebook group. Direct links to the documents are provided below.

Odonate Exuviae – a hyperlinked list of identification guides to many species of odonate exuviae from seven families of dragonflies and three families of damselflies.

Tech Tips

The photograph featured in this blog post is a “one-off,” that is, a single photo rather than a focus-stacked composite image. The camera lens was set for f/16; the camera body was set for ISO 160 and a shutter speed of 1/250 s.

The photo was taken using a Fujifilm X-T3 digital camera, Fujifilm MCEX-11 extension tube, Fujinon XF80mm macro lens (120mm, 35mm equivalent), and an array of external lights.

Two external flash units were used to create the white background by cross lighting the front of a piece of white plastic; another flash was used to light the subject. A Sunpack LED 160 was used as a focusing aid.

RAW FILE CONVERTER EX 3.0 was used to convert one RAW (RAF) file to a TIFF file. The TIFF file was edited using Apple Aperture and sharpened using Photoshop.

Copyright © 2021 Walter Sanford. All rights reserved.

MYN – Hylogomphus adelphus exuvia (dorsal)

May 4, 2020

The following Anisoptera exuvia — collected by Freda van den Broek on 10 June 2019 along the St. Croix River in Polk County, Wisconsin USA — is definitely a member of Family Gomphidae (Clubtails), probably Mustached Clubtail (Hylogomphus adelphus).

Dorsal view

The abdomen is wider than the head. Vestigial mid-dorsal hooks are noticeable along several abdominal segments, especially segment nine (S9). A “median groove” is apparent along part of the abdomen. The lateral spine on S9 is spinulose-serrate along the outer edge.

10 JUN 2019 | Polk County, WI | H. adelphus exuvia (dorsal)

Related Resources

Tech Tips

This subject was photographed against a pure white background (255, 255, 255) using the “Meet Your Neighbours” (MYN) technique.

15 photos of the specimen were taken using an aperture of f/16; in-camera focus peaking was used to highlight select areas in each photo. Adobe Photoshop CC 2017 was used to create- and annotate the focus-stacked composite image shown above.

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Too dark or too light?

April 27, 2020

The following Anisoptera exuvia — collected by Freda van den Broek on 10 June 2019 along the Red Cedar River in Barron County, Wisconsin USA — is definitely a member of Family Gomphidae (Clubtails), possibly Rusty Snaketail (Ophiogomphus rupinsulensis).

Dorsal-lateral view

Nine (9) photos of the specimen were taken using an aperture of f/16; in-camera focus peaking was used to highlight select areas in each photo. Adobe Photoshop CC 2017 was used to create the focus-stacked composite image shown below.

10 JUN 2019 | Barron County, WI | Anisoptera exuvia (dorsallateral)

When I previewed the RAW files used to create the preceding composite image, I thought most of the files look too dark.

So I did a do-over using 15 photos, resulting in a new version of the composite that is perfectly in focus but a little too light. Compare/contrast the two composite images and you should notice it’s easier to see the mid-dorsal hooks along the abdomen in the first image. The primary purpose for the images is to illustrate those field marks, therefore I think the first (darker) image is better.

10 JUN 2019 | Barron County, WI | Anisoptera exuvia (dorsallateral)

Face-head-dorsal view

Five (5) photos of the specimen were taken using an aperture of f/16; in-camera focus peaking was used to highlight select areas in each photo. Adobe Photoshop CC 2017 was used to create the focus-stacked composite image shown below.

10 JUN 2019 | Barron County, WI | Anisoptera exuvia (face-head-dorsal)

My first impression of the version shown above is it’s too dark, and I second-guessed myself for not shooting more photos for the focus stack.

I created a new focus-stacked composite image using a little more light and 14 photos. When I examined the RAW files used to create the new composite image (shown below), I thought most of the files still look too dark. (But I was wrong.)

10 JUN 2019 | Barron County, WI | Anisoptera exuvia (face-head-dorsal)

So I created a third version using much more light and 24 photos. Although it’s debatable which image looks best, the first- and second images show a few key field marks of the antennae better than the third image.

It turns out the antennae are one indicator this specimen is from the genus Ophiogomphus (Snaketails), so the first two (darker) images are the winners once again.

10 JUN 2019 | Barron County, WI | Anisoptera exuvia (face-head-dorsal)

For what it’s worth, the second of three images is my favorite as indicated by the fact that the image is cropped so there’s room for annotations.

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Clubtail exuvia (dorsal-lateral view)

April 24, 2020

The following Anisoptera exuvia — collected by Freda van den Broek on 10 June 2019 along the Red Cedar River in Barron County, Wisconsin USA — is definitely a member of Family Gomphidae (Clubtails), possibly Rusty Snaketail (Ophiogomphus rupinsulensis).

10 JUN 2019 | Barron County, WI | Anisoptera exuvia (dorsallateral)

Notice the exuvia has little stubby mid-dorsal hooks along the length of its abdomen, and lateral spines on abdominal segments seven through nine (S7-S9).

Tech Tips

This subject was photographed against a pure white background (255, 255, 255) using the “Meet Your Neighbours” (MYN) technique.

15 photos of the specimen were taken using an aperture of f/16; in-camera focus peaking was used to highlight select areas in each photo. Adobe Photoshop CC 2017 was used to create the focus-stacked composite image shown above.

Copyright © 2020 Walter Sanford. All rights reserved.

Neurocordulia yamaskanensis exuvia

April 13, 2020

A Stygian Shadowdragon dragonfly (Neurocordulia yamaskanensis) exuvia was collected by Freda van den Broek on 10 June 2019 along the St. Croix River in Interstate Park, Polk County, Wisconsin USA.

A two-step process was used to verify 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 Corduliidae (Emeralds).

  • The specimen has a mask-like labium (prementum) that covers the face, as shown in Image No. 1, characteristic of four families of odonates: Cordulegastridae (Spiketails); Corduliidae (Emeralds); Libellulidae (Skimmers); and Macromiidae (Cruisers).
  • There is no horn on the face-head, characteristic of Macromiidae, so it’s not a cruiser.
  • Cordulegastridae has angular, jagged crenulations on its labium, so it’s not a spiketail. The crenulations for Corduliidae and Libellulidae can look similar.
  • Look at the anal pyramid to differentiate Corduliidae and Libellulidae: 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, and no horn on its face-head. The deeply-scalloped crenulations along the margins of the palpal lobes are a characteristic field mark for Genus Neurocordulia (Shadowdragons) in the Family Corduliidae (Emeralds), according to Kevin Hemeon, member of the “Odonate Larvae and Exuviae” Facebook group.

Although the anal pyramid isn’t shown clearly in any of the photos in this field guide, careful examination of photos of the teneral adult that emerged from the exuvia (see The Backstory, below) confirmed the dragonfly is a Stygian Shadowdragon. Stygian is the only species of Neurocordulia (Shadowdragons) within range of Wisconsin.

A face-head view of the exuvia is shown in Image No. 1, magnified approximately two and one-half times life size (~2.5x). Notice the mask-like labium that covers the face of the exuvia, including deeply-scalloped crenulations with bundles of bristles (setae) located along the margins of the palpal lobes.

No. 1 | Neurocordulia yamaskanensis | exuvia (face-head)

Step 2. Genus and species

Dichotomous keys from Identification Keys to Northeastern Anisoptera Larvae, compiled by Ken Soltesz, were used to verify the genus and species of the exuvia. Field marks that match this specimen are highlighted in boldface green text.

Key to the Genera of the Family Corduliidae, p. 28.

1a. Pair of small tubercles on top of head; Lateral lobe of labium with 4 or 5 setae (except sometimes 6 or 7 in Neurocordulia). (2)

2a. Strong lateral spines of abdominal segment 8 very divergent and as strong as parallel spines of [S]9. (Neurocordulia)

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

1a. Dorsal hooks present and well developed on some of the abdominal segments. (2)

2a. Lateral spines present on segment 8. (3)

3a. Crenulations on distal margin of labial palpi nearly semicircular or even more deeply cut; Lateral spines on segment 8 divergent. (Neurocordulia)

Key to the Species of the Genus Neurocordulia, p. 31.

1b. Lateral spines of 9 about 30 to 50 percent of the length of segment 9, not extending beyond the tips of the caudal appendages; Dorsal hooks of segments 7 to 9 reduced to scarcely more than a short ridge; Length 22 – 24.5 mm. (yamaskanensis)

The following annotated focus-stacked composite images illustrate key field marks described in Soltesz’s dichotomous keys.

Notice the specimen has stubby mid-dorsal hooks along the length of its abdomen, as shown in Image No. 2.

Lateral spines are present on abdominal segments eight and nine (S8-S9): the lateral spines on S8 are divergent; the ones on S9 are parallel.

The exuvia is ~2.4 cm (~0.95 in) in length — the longest shadowdragon larva/exuvia in the genus Neurocordulia. Notice the lateral spines on abdominal segment nine (S9) don’t extend beyond the tips of the caudal appendages (terminal appendages), as shown below.

The Backstory

The following narrative was provided by Freda van den Broeck.

On the last morning of the Wisconsin Dragonfly Society Annual Meeting weekend — Sunday, June 10th 2019 — I made my way to the boat landing in Interstate Park, St. Croix Falls, Wisconsin USA.

The previous morning I’d photographed Mustached Clubtail emerging there (with Alon Coppens). We also saw several teneral Rapids Clubtails. One didn’t have to look hard to find exuviae — they were most easily seen on the rocks, just a couple of feet above the water line. I was really hoping to find a Snaketail emerging, but had no such luck.

Photo of St. Croix river used with permission from Freda van den Broek.

Just as I was about to head back to the car, I spotted a teneral, that had crawled up the rock face higher than I would have expected. At that point, I thought it was “just another baskettail” — we’d seen many of them on Friday afternoon and Saturday. But it was pretty and shiny, so I had to take a few pictures, even though I was late for breakfast. (It was around 8:20 am.)

It was several days later before I realized that it wasn’t a baskettail, but a Shadowdragon, and that a few of the exuviae I’d collected there were Stygian Shadowdragons. Source Credit: Freda van den Broek.

Photo used with permission from Freda van den Broek.

Tenerals are usually tough to identify, but you’ll notice in both photos that the [small yellow] spot on [side of] the thorax is clearly visible. Source Credit: Freda van den Broek.

Photo used with permission from Freda van den Broek.

Related Resources

Odonate Exuviae – a hyperlinked list of identification guides to many species of odonate exuviae from seven families of dragonflies and three families of damselflies.

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – N. yamaskanensis exuvia (dorsal, ventral)

April 8, 2020

A Stygian Shadowdragon dragonfly (Neurocordulia yamaskanensis) exuvia was collected by Freda van den Broek on 10 June 2019 along the St. Croix River in Interstate Park, Polk County, Wisconsin USA.

Dorsal

The first dorsal view is a square crop of the full-size version of a focus-stacked composite image of the subject. Notice the specimen has stubby mid-dorsal hooks along the length of its abdomen and lateral spines on abdominal segments eight (S8) and nine (S9).

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

The original full-size image, shown below, was straightened and cropped slightly.

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

Ventral

The first ventral view is a square crop of the full-size version of a focus-stacked composite image of the subject. Notice the compact size of the prementum, and its unusual shape.

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

The original full-size image, shown below, was cropped slightly.

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

Related Resources

Tech Tips

This subject was photographed against a pure white background (255, 255, 255) using the “Meet Your Neighbours” (MYN) technique.

Three (3) photos were used to create the dorsal composite image, including a single photo focused on the head/thorax, and two places along the abdomen (S5-S6 and S9).

13 photos were used to create the ventral composite image, including multiple photos focused on the prementum, thorax, and two places along the abdomen (S3-S4; S7-S8).

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – N. yamaskanensis exuvia (dorsal-lateral)

April 6, 2020

The following focus-stacked composite image shows a dorsallateral view of a Stygian Shadowdragon dragonfly (Neurocordulia yamaskanensis) exuvia collected by Freda van den Broek on 10 June 2019 along the St. Croix River in Interstate Park, Polk County, Wisconsin USA.

10 JUN 2019 | Polk County, WI | Stygian Shadowdragon (exuvia)

Notice the specimen has stubby mid-dorsal hooks along the length of its abdomen and lateral spines on abdominal segments eight (S8) and nine (S9).

Related Resources

Tech Tips

This subject was photographed against a pure white background (255, 255, 255) using the “Meet Your Neighbours” (MYN) technique.

Four (4) photos were used to create the composite image, including a single photo focused on the head, thorax, and two places along the abdomen (S6-S7 and S9-S10).

Copyright © 2020 Walter Sanford. All rights reserved.


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