Archive for April, 2020

MYN – Hylogomphus adelphus exuvia

April 29, 2020

An Anisoptera exuvia was collected by Freda van den Broek on 10 June 2019 along the St. Croix River in Polk County, Wisconsin USA.

This specimen is definitely a member of Family Gomphidae (Clubtails), probably Mustached Clubtail (Hylogomphus adelphus).

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

Related Resources

Tech Tips

This subject was photographed against a pure white background (255, 255, 255) using the “Meet Your Neighbours” (MYN) technique. This photo is a “one-off,” that is, not a composite image.

Eight (8) 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 will be used to create a focus-stacked composite image of the exuvia.

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.

MYN – Clubtail exuvia (ventral view)

April 22, 2020

An Anisoptera exuvia was collected by Freda van den Broek on 10 June 2019 along the Red Cedar River in Barron County, Wisconsin USA.

This specimen is definitely a member of Family Gomphidae (Clubtails), possibly Rusty Snaketail (Ophiogomphus rupinsulensis).

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

Notice the exuvia has a flat labium (prementum). There are lateral spines located 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.

Seven (7) 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.

Cobra Clubtail versus Midland Clubtail

April 20, 2020

Odonate exuviae from two species in Genus GomphurusCobra Clubtail (Gomphurus vastus) and Midland Clubtail (Gomphurus fraternus) — are nearly perfect body doubles, with the exception of one key field mark that can be used to differentiate the species.

Dorsal views

Lateral spines are located on abdominal segments six through nine (S6-S9) for both species.

10 JUN 2019 | Barron County, WI | Midland Clubtail exuvia (dorsal)

Ventral views

The overall shape of the prementum is similar for both species.

10 JUN 2019 | Barron County, WI | Midland Clubtail exuvia (ventral)

Prementum (ventral view)

The shape of the palpal lobes on the prementum is different for the two species, as shown in the following diagram on p. 15, Key to the species of genus GomphurusIdentification Keys to Northeastern Anisoptera Larvae, compiled by Ken Soltesz.

The following images are magnified approximately three and one-half times life size (~3.5x).

For both species, focus on the row of teeth along the right palpal lobe. Notice the strongly curved shape of the palpal lobe for Cobra Clubtail (shown above), in contrast with the gently arched shape of the palpal lobe for Midland Clubtail (shown below). Also notice the Cobra palpal lobe has fewer teeth than Midland.

10 JUN 2019 | Barron County, WI | Gomphurus fraternus (exuvia)

Adults

Adult Cobra Clubtail dragonflies are almost identical to Midland Clubtails too. Several field marks can be used to differentiate the two species. In my opinion, one field mark is the easiest to recognize where it really matters — in the field!

16 MAY 2016 | Riverbend Park | Cobra Clubtail (adult male)

Notice there aren’t any mid-dorsal marks on abdominal segments eight and nine (S8-S9) for Cobra Clubtail (shown above). In contrast, there is a small yellow triangle on abdominal segment eight (S8) for Midland Clubtail (shown below). This is true for males and females of both species.

Photo used with permission from Freda van den Broek.

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Clubtail exuvia (dorsal view)

April 17, 2020

An Anisoptera exuvia was collected by Freda van den Broek on 10 June 2019 along the Red Cedar River in Barron County, Wisconsin USA.

This specimen is definitely a member of Family Gomphidae (Clubtails), possibly Midland Clubtail (Gomphurus fraternus).

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

Notice there are no mid-dorsal hooks. Lateral spines are located on abdominal segments six through nine (S6-S9).

The case for Midland Clubtail is looking stronger based upon a close-up of the prementum that will be published in my next blog post.

Related Resource: MYN – Clubtail exuvia (species unknown)

Tech Tips

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

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Clubtail exuvia (species unknown)

April 15, 2020

An Anisoptera exuvia was collected by Freda van den Broek on 10 June 2019 along the Red Cedar River in Barron County, Wisconsin USA.

This specimen is definitely a member of Family Gomphidae (Clubtails), possibly Midland Clubtail (Gomphurus fraternus).

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

Tech Tips

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

During this photo shoot, I tested the Flash Diffuser Light Softbox by Altura Photo (6″ x 5″) for the first time. This relatively inexpensive softbox ($12.99) is highly recommended by Allan Walls, an excellent photographer who specializes in macro photography. I must admit I was more than a little skeptical but the diffuser seems to work as advertised and is a remarkable bargain, unlike my expensive Lastolite softbox flash modifiers (8.5” x 8.5” square).

The 1:1 rule-of-thumb is used to determine how close/far to position a flash unit from the subject. The diagonal distance across the face of a softbox should be the distance to the subject [or less] for soft wrap-around light. Actually, the distance should be as close as possible without the softbox showing in the photo frame. Greater distances will result in a contrasty look.

For example, my new Altura softbox is a 6” x 5” rectangle (7.8” diagonally) so it should be positioned ~8″ or less from the subject. Buyer beware: This distance is OK for macro photography but not OK for most other types of photography.

Related Resources

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 (face-head)

April 10, 2020

The following annotated focus-stacked composite image shows 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 unusual shape of the crenulations between the palpal lobes of its mask-like labium. Is this field mark unique to N. yamaskanensis or common to all species of the genus Neurocordulia (Shadowdragons)? Enquiring minds want to know!

Tech Tips

Laowa 25mm Ultra Macro lens, set for 2.5x magnification, and Canon EOS 5D Mark II DSPLR was used to photograph the subject against a pure white background (255, 255, 255) following the “Meet Your Neighbours” (MYN) technique.

24 photos were used to create the composite image, including 23 photos taken using an aperture of f/5.6 and one photo taken at f/16.

If you look closely at the full-size version of the image, then you will notice some areas that indicate the final image is a few layers short of a perfect focus stack. But hey, not bad for a new lens and a manual focus rail that I used for the first time!

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.


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