Posts Tagged ‘dorsal hooks’

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.

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.

MYN – Dragonfly exuvia (unknown species)

February 24, 2020

An exuvia from an unknown species of odonate was collected by Joe Johnston on 07 August 2019 along Aquia Creek at Channel Marker No. 34, Stafford County, Virginia USA.

The specimen is definitely a dragonfly, probably from either Family Corduliidae (Emeralds) or Family Libellulidae (Skimmers).

07 AUG 2019 | Aquia Creek | dragonfly exuvia (face-head-dorsal view)

This relatively small exuvia is ~1.2 to 1.3 cm in length. Notice the dorsal hooks on the exuvia are “cultriform,” that is, shaped like a pruning knife.

07 AUG 2019 | Aquia Creek | dragonfly exuvia (lateral view)

Related Resource: Odonate exuviae collecting sites [along Aquia Creek]

Tech Tips

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

I experimented with a new variation on my old MYN studio rig. The new set-up seems to work well, although the question remains “Does it work well consistently?” I added a second external flash unit that is used to backlight a piece of translucent white plastic (the background), and I physically separated the clear plastic “stage” from the white background. More info and photos will be featured in a follow-up blog post.

Copyright © 2020 Walter Sanford. All rights reserved.

Building a case for Slaty Skimmer

October 23, 2019

With each new photo set of this unknown species of odonate exuvia, a case is building slowly for Slaty Skimmer (Libellula incesta).

Occoquan Regional Park | unknown species | exuvia (lateral)

A piece of white schmutz was removed from the tip of the abdomen, enabling a clearer view of abdominal segment nine (S9). Look closely at the two photos featured in this post. Notice there are stubby mid-dorsal hooks (not cultriform) on abdominal segments four through eight (S4-S8).

Occoquan Regional Park | unknown species | exuvia (dorsal)

The last photo shows a closer view of the anal pyramid. Notice the lateral caudal appendages (cerci) are less than half as long as the inferior appendages (paraprocts).

Soltesz, p. 43 – Key to the Species of the Genus Libellula

Field marks that match this specimen are highlighted in boldface green text.

1b. Dorsal hooks regularly present on segments 4 to 8. [2]
2b. Palpal setae 5 (sometimes 6 in cyanea). [5]
5a. Epiproct distinctly decurved at tip. [6]
6b. Length of last instar about 26mm; cerci less than half as long as paraprocts. [incesta]

Punch List

I need to look at the inside of the labium (face mask) in order to count palpal setae. The epiproct must be cleaned to see whether it is decurved. This exuvia was deformed as a result of emergence, so it’s impossible to make an accurate measurement of the length of the specimen. That said, the exuvia is more than 22.0 mm (0.9 in) long. (22 mm is the length of the last instar for L. cyanea.)

And of course, I need to annotate all of the images in this series of blog posts in order to illustrate the unfamiliar vocabulary that is used in virtually all dichotomous identification keys.

Related Resources

Tech Tips

The following equipment was used to shoot the quick-and-dirty macro photographs featured in this post: Fujifilm X-T1 digital camera; Fujifilm MCEX-16 extension tube; and Fujinon XF80mm macro lens plus lens hood. The camera was set for both manual exposure and manual focus. That’s right, a switch on the camera body is used to set the type of focus. It’s a Fujifilm thing. Camera settings: focal length 80mm (120mm, 35mm equivalent); ISO 200; f/16; 1/180s.

Godox X2TF radio flash trigger, mounted on the hotshoe of my X-T1, was used to control two off-camera external flash units set for radio slave mode: Godox TT685F Thinklite TTL Flash (manual mode); and Godox TT685o/p Thinklite Flash for Olympus/Panasonic Cameras (manual mode). Both flash units were fitted with a Lastolite Ezybox Speed-Lite 2 flash modifier.

Adobe Photoshop CC 2017 was used to spot-heal and sharpen the image.

Copyright © 2019 Walter Sanford. All rights reserved.

Unknown species of odonate exuvia, revisited

October 18, 2019

This post features more photos of an odonate exuvia collected by Michael Powell during a photowalk with me on 01 June 2019 at Occoquan Regional Park, Fairfax County, Virginia USA. Both photos are one-offs, not composite images.

The genus and species is unknown. This specimen might be a member of Family Libellulidae (Skimmers).

Occoquan Regional Park | unknown species | exuvia (lateral)

Mid-dorsal hooks are present on some abdominal segments. Lateral spines are located on abdominal segments eight and nine (S8-9).

Occoquan Regional Park | unknown species | exuvia (dorsal)

I still need to take close-up photos of the anal pyramid and shoot photos of the ventral view before I attempt to identify the genus/species of the specimen using one or more dichotomous keys.

Related Resource: Vimeo video: Identifying dragonfly larva to family (8:06).

Tech Tips

The following equipment was used to shoot the quick-and-dirty macro photograph featured in this post: Fujifilm X-T1 digital camera; Fujifilm MCEX-16 extension tube; and Fujinon XF80mm macro lens plus lens hood. The camera was set for both manual exposure and manual focus. That’s right, a switch on the camera body is used to set the type of focus. It’s a Fujifilm thing. Camera settings: focal length 80mm (120mm, 35mm equivalent); ISO 200; f/16; 1/180s.

Godox X2TF radio flash trigger, mounted on the hotshoe of my X-T1, was used to control two off-camera external flash units set for radio slave mode: Godox TT685F Thinklite TTL Flash (manual mode); and Godox TT685o/p Thinklite Flash for Olympus/Panasonic Cameras (manual mode). Both flash units were fitted with a Lastolite Ezybox Speed-Lite 2 flash modifier.

Adobe Photoshop CC 2017 was used to spot-heal and sharpen the image.

Copyright © 2019 Walter Sanford. All rights reserved.

Dromogomphus spinosus exuvia

June 28, 2019

A dragonfly exuvia was collected by Joe Johnston on 22 May 2019 at Aquia Creek, Stafford County, Virginia USA. This specimen is the cast skin from a Black-shouldered Spinyleg (Dromogomphus spinosus) larva. D. spinosus is a member of Family Gomphidae (Clubtails).

Black-shouldered Spinyleg (Dromogomphus spinosus) | exuvia (dorsal)

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!

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.

The Backstory

Joe Johnston is an avid boater and sport fisherman who kindly agreed to be my “Eyes on the Aquia,” always on the lookout for odonate exuvia to share with me. On 22 May 2019 Joe caught a largemouth bass that swam around one of the wooden pilings of a boat dock that extends far into Aquia Creek. The fishing line was snagged on the piling so Joe moved his boat into position to free the fish. That’s when he noticed the exuvia clinging to a piling on the underside of the dock. Good catches, Joe!

Tech Tips

The following equipment was used to shoot the quick-and-dirty handheld macro photograph featured in this post: Fujifilm X-T1 digital camera; and Fujinon XF80mm macro lens plus lens hood. The camera was set for both manual exposure and manual focus. That’s right, a switch on the camera body is used to set the type of focus. It’s a Fujifilm thing. Actually, back-button focus was used to autofocus the image and adjusted manually as necessary. That’s also a Fujifilm thing. Camera settings: focal length 80mm (120mm, 35mm equivalent); ISO 200; f/9; 1/180s.

Godox XProF radio flash trigger, mounted on the hotshoe of my X-T1, was used to control an off-camera Godox TT685 Thinklite TTL Flash (TT685F) set for radio slave mode. The flash was fitted with a Lastolite Ezybox Speed-Lite 2 flash modifier.

Adobe Photoshop CC 2017 was used to spot-heal and sharpen the image, plus add annotations.

Sometime in the future (probably the odonate “off-season”) I will create higher quality composite images of this exuvia, shown from all viewpoints including the ventral view. As it turns out, the dorsal view is sufficient to identify this species.

Copyright © 2019 Walter Sanford. All rights reserved.


%d bloggers like this: