Archive for the ‘How To’ Category

“Tech Tips” Tuesday

November 30, 2021

In this blog post I’m going to show you how I add special characters to some of my annotated images, such as the pictograph for “male,” shown below.

Photo used with written permission from Michael Powell.

I’ll show you how to do it on my older Apple 24″ iMac desktop computer (Early 2009), then I’ll show you how to do the same thing on my newer Apple 13″ MacBook Air laptop computer (M1, 2020).

macOS Yosemite (Version 10.10.5)

Open “System Preferences” and select “Keyboard.” Click on the tab labeled “Keyboard” and check the box for “Show Keyboard & Character Viewers in menu bar.”

As you might expect, a new icon will appear in the menu bar, located on the right side of the screen. When you click on the icon you should see three (3) options (listed from top-to-bottom): Show Character Viewer; Show Keyboard Viewer; and Open Keyboard Preferences… Select “Character Viewer” and navigate to Pictographs. (The last option takes you back the same screen that is shown above.)

macOS Monterey (Version 12.0.1)

After I was unable to figure out how to make the same setting on my MacBook Air, I referred to the “macOS User Guide” that is a built-in feature of the computer. A screenshot of the guide is shown below.

Open “System Preferences” and select “Keyboard.” Click on the tab labeled “Input Sources” and check the box for “Show Input menu in menu bar.”

A new icon will appear in the menu bar, located on the right side of the screen. When you click on the icon you should see the three (3) options shown below. Select the first option, “Show Emoji & Symbols.”

A new window will open on-screen. Navigate to Pictographs. Some sample Pictographs are shown below, including the female and male symbols (fifth row from the top).

Practical example using Photoshop

Here’s an example of part of my workflow to annotate a photograph using Adobe Photoshop.

Open a photo file in Photoshop. Select the “Text Tool” and create a new layer called “male symbol.” Click on the image to add an insertion point, then click on the icon in the computer menu bar and select “Show Emoji & Symbols.” Navigate to “Pictographs” and select the “male sign.” You should see a list of “Font Variations.” I always use “Arial Bold.” Double-click on the icon and it should appear on the photo. ♂ Use the “Move Tool” to, well, move the symbol wherever you like on the image.

Photopea

I stumbled across an application recently called “Photopea” that is a free alternative to Adobe Photoshop. Photopea is a Web-based clone of Photoshop — Photopea doesn’t do everything Photoshop does but it could be used to annotate photos using a workflow similar to the one I just described. Look for one or more Photopea-related blog posts in the near future.

Related Resource

Anatomy of a male Tiger Spiketail – a blog post by Walter Sanford.

Copyright © 2021 Walter Sanford. All rights reserved.

Dark and moody

November 19, 2021

I spotted an emergent Uhler’s Sundragon (Helocordulia uhleri) during a photowalk along a mid-size stream at an undisclosed location in Prince William County, Virginia USA. The following photograph shows the exuvia from which the teneral adult eclosed.

13 APR 2021 | PNC. Wm. County, VA | Uhler’s Sundragon | exuvia (ventral)

In the opinion of the author, larvae (nymphs)/exuviae from Family Corduliidae (Emeralds) and Family Libellulidae (Skimmers) can be challenging to differentiate and identify to the family level.

One way to differentiate Emerald from Skimmer larvae/exuvia is to look for a “ventromedial groove” in the prementum: it’s probably Corduliidae (Emeralds) if there is a ventromedial groove; it’s probably Libellulidae if there isn’t.

Look closely at a version of the preceding photo that was reformatted, rotated, and cropped to show an enlarged view of the prementum. You should notice a ventromedial groove on the basal half of the prementum, indicating this specimen is a member of Family Corduliidae (Emeralds).

13 APR 2021 | PNC. Wm. County, VA | Uhler’s Sundragon | exuvia (ventral)

Three raised structures on the underside of the prementum remind me of the hood ornament on a 1949 Lincoln automobile. (No, I wasn’t alive in 1949!)

Related Resources

Tech Tips

One reason I underexposed the photo is to add definition to the ventromedial groove and avoid overexposing the black background.

I prefer a white background for photographing odonate exuviae. Using a black background proved to be more challenging than I expected. More later in a follow-up blog post.

Copyright © 2021 Walter Sanford. All rights reserved.

How to estimate instar, revisited

November 16, 2021

I’m the founder and co-administrator of the Odonate Larvae and Exuviae Facebook group. Friday, 12 November 2021 was the two-year anniversary of the group. As of this writing there are approximately 1,700 members in the group, including people from around the world.

For example, Abiodun Matthew Adedapo from Nigeria. Abiodun began posting to the group relatively recently, sharing information and photos related to his research. Sincere thanks to Abiodun for permission to repurpose two of his photos for another mini-lesson on how to estimate instar.

What is the instar? Not F-0.

The equation for instar equivalent is as follows.

Instar equivalent = HwL / HW

Where HwL is Hind wing Length and HW is Head Width.

 

Photo used with written permission from Abiodun Matthew Adedapo.

I used the Adobe Photoshop “Ruler Tool” to measure the number of pixels along the two double-tipped white arrows shown in the preceding annotated image of a preserved specimen collected and photographed by Abiodun.

HwL is ~132.6 pixels. HW is ~195.12 pixels.

Instar equivalent = 132.6 pixels / 195.12 pixels

The units cancel, so the answer is ~0.68 — close to Ken Tennessen’s  average value for F-1 (final instar minus one).

Abiodun reported the instar as F-2, based upon in situ observations of a cohort of larvae (nymphs) from Family Gomphidae (Clubtails).

For my purpose, it doesn’t matter whether the actual instar is either F-1 or F-2 — the important take-away is we know the instar is not F-0, the final instar. This provides an opportunity to mention a simpler way to estimate final instar.

Larvae in the final stage can be recognized by the length of the wing buds which cover the fourth abdominal segment. Source Credit: Field Guide to the larvae and exuviae of British Dragonflies, by Steve Cham, p. 30.

Look closely at the first annotated image. Notice the length of the wing buds/pads doesn’t reach the fourth abdominal segment (S4) of the specimen therefore this larva is not in its final instar.

Thanks to Freda van den Broek for sharing this method with me!

F-0 (final instar)

The last annotated image shows part of a different larva also collected and photographed by Abiodun. Notice the length of the wing buds/pads does reach S4, therefore this larva is in its final instar.

Photo used with written permission from Abiodun Matthew Adedapo.

Related Resource: How to estimate instar, a blog post by Walter Sanford.

Copyright © 2021 Walter Sanford. All rights reserved.

Mouth parts – Tiger Spiketail exuvia

November 12, 2021

I revisited a photograph featured in a blog post published several years ago. I wanted to annotate the image to include information that I learned recently.

The following annotated image shows the face and mouth of an exuvia from a Tiger Spiketail dragonfly (Cordulegaster erronea) after its scoop-shaped face mask was pulled away from the head in order to count setae on the inner side of the prementum.

Cordulegaster erronea | exuvia (face and mouth)

There are two mandibles, one located on each side of the labrum. And there are two maxilla, one located below each mandible. Coarse setae make it challenging to see all of the parts clearly.

Sincere thanks to Marla Garrison for verifying my tentative identification of these mouth parts. And of course, thanks to Mike Boatwright for collecting and sharing the specimen with me.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Post update: What is it — emerald or skimmer?

November 5, 2021

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

The presence of a ventromedial groove in the prementum suggests this specimen is a member of Family Corduliidae (Emeralds) and in fact it is.

Congratulations to Douglas Mills, who correctly identified the family of this specimen.

Going with corduliidae for the groove. It’s got impressive crenulations — I had to double check they weren’t jagged and this was a trick question 🙂 Source Credit: Douglas Mills.

Douglas successfully avoided the trap that was set when I chose to use a specimen that features deeply-scalloped crenulations along the margins of the palpal lobes. According to Kevin Hemeon, member of the “Odonate Larvae and Exuviae” Facebook group, crenulations like these are a characteristic field mark for Genus Neurocordulia (Shadowdragons) in the Family Corduliidae (Emeralds).

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

What is it — emerald or skimmer?

November 2, 2021

Ladies and gentlemen, children of all ages. It’s time for another exciting episode of “What is it?

I wrote about the “ventromedial groove” in a recent blog post. Based upon what you learned, is the following odonate exuvia a member of Family Corduliidae (Emeralds) or Family Libellulidae (Skimmers)?

Odonata (Suborder Anisoptera) | exuvia (face-head)

If you think you know the family, then please leave a comment. The answer will be revealed in a post update.

Copyright © 2021 Walter Sanford. All rights reserved.

How to estimate instar

October 29, 2021

Most odonate larvae (nymphs) go through 10-13 stages of development known as “instars.” F-0 is the final instar, F-1 the preceding instar, and so forth.

Sidebar

The “F” in the name for every instar stands for Final. “F-0” is the final instar. “F-1” means final instar minus one, that is, the stage that precedes the final instar. “F-2” means two stages before the final instar.

Ken Tennessen, author of Dragonfly Nymphs of North America: An Identification Guide, devised a method for determining instar by examining hind wing length and head width.

Calculating the ratio between hind wing length and head width results in a number that is approximately equivalent to instar, that is, assuming you know how to interpret the result¹.

The equation for instar equivalent is as follows.

Instar equivalent = HwL / HW

Where HwL is Hind wing Length and HW is Head Width.

Math Tips

Fractions are read from top-to-bottom, or when written as shown above, left-to-right. The equation literally says “Instar equivalent equals Hind wing Length divided by Head Width.”

The equation is units independent, meaning any units of measurement can be used as long as the same units are used above and below the dividing line. Instar equivalent is a dimensionless number because the units cancel during division. (Remember “dimensional analysis” from chemistry and physics?)

For most of the life of an odonate larva (nymph) its head is wider than the length of its wing pads. Therefore instar equivalent is calculated by dividing a smaller number by a larger number, resulting in a decimal fraction. As the wing pads grow, the instar equivalent increases until the ratio is approximately 1:1 (or slightly larger) at F-0, the final instar.

¹According to empirical data collected by Tennessen, average instar equivalents are as follows: ≥1.00 for F-0; 0.66 for F-1; 0.50 for F-2; 0.33 for F-3; and 0.25 for F-4. Remember, these numbers are averages — your mileage might vary.

Theory into practice

Cordulegaster sp. larva (female) | dorsal view

I used the Adobe Photoshop “Ruler Tool” to measure the number of pixels along the two double-tipped white arrows shown in the preceding annotated image of a preserved specimen.

Tech Tips

60s ‘shop: Using the ruler tool to measure distances in Photoshop CC, by Photoshop for the Scientist (1:00) provides a clear and concise explanation of how it’s done.

HwL is ~920.81 pixels. HW is ~911.15 pixels.

Instar equivalent = 920.81 pixels / 911.15 pixels

The units cancel, so the answer is ~1.01 — close enough to the average value for F-0 (final instar). Easy, huh?

What are the take-aways?

  1. An instar of F-0 indicates the spiketail larva featured in this blog post was nearer the end of the larval phase of its life than the beginning. Time is dilated for larvae in the Family Cordulegastridae (Spiketails), so it’s difficult to say how much longer it would have been until the larva metamorphosed into an adult.
  2. Every odonate exuvia is a cast skin of the larva at F-0, the final instar, before it ecloses to become an adult. Therefore the instar equivalence for all exuviae should be ≥1.00. Try it and see!

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Anal pyramid

October 26, 2021

The “anal pyramid” is a more-or-less triangularly-shaped group of five appendages on the posterior end of dragonfly larvae (nymphs) and exuviae, including one epiproct, two cerci (sing. cercus), and two paraprocts.

The author suggests either “posterior pyramid” or “posterior triangle” as a less offensive sounding collective name for these anatomical parts. The author is just saying.

Although the anal pyramid isn’t always shaped like a perfect equilateral triangle, as shown above (in white), it always features the same five component body parts. These parts are often critical for identifying odonate larvae (nymphs) and exuviae.

Glossary

 


The Backstory

The Eastern Ringtail dragonfly (Erpetogomphus designatus) exuvia shown above was collected along the Potomac River at Riverbend Park, Fairfax County, Virginia USA. This species is a member of Family Gomphidae (Clubtails). I created a photo-illustrated identification guide for E. designatus using the same specimen.

Copyright © 2021 Walter Sanford. All rights reserved.

Cordulegaster sp. larva

October 22, 2021

Odonates are aquatic insects. They spend most of their life as larvae (nymphs) that live in water; this stage of their life cycle can last from a few months to a few years. Finally, they emerge from the water and metamorphose into adults in order to reproduce; their offspring return to the water and the cycle begins again.

This post features annotated images of a larva (nymph) from the Family Cordulegastridae (Spiketails) that was collected and reared by Bob Perkins. The larva died before it metamorphosed into an adult.

The distinctive jagged crenulations on the face mask of spiketails are unmistakeable!

Cordulegaster sp. larva (preserved specimen) | face-head

This individual is a female, as indicated by her developing ovipositor that can be seen on the ventral side of the specimen along the boundary between abdominal segments eight and nine (S8, S9).

Cordulegaster sp. larva (female) | ventral view

The presence of a ventromedial groove in the prementum is a reliable field mark for larvae/exuviae in Family Corduliidae (Emeralds). Some species of larvae/exuviae in other families of dragonflies, such as Family Cordulegastridae (Spiketails), feature a ventromedial groove in the prementum. In this case, the presence of a ventromedial groove does not indicate this specimen is an Emerald.

Most odonate larvae go through 10-13 stages of development known as “instars.” The author lacks sufficient experience to identify the instar of this specimen, although it appears to be one of the later stages as indicated by its well-developed wing pads, shown below.

Post Update: According to Ken Tennessen, author of Dragonfly Nymphs of North America: An Identification Guide, F-0 is the instar of this specimen (final instar). Thanks, Ken!

Cordulegaster sp. larva (female) | dorsal view

Larvae (nymphs)/exuviae in Family Cordulegaster (Spiketails) are burrowers, as indicated by the dirty, sediment-covered dorsal side and relatively clean ventral side of this specimen.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Relative length of cerci versus paraprocts

October 19, 2021

A quote from my last blog post sets the stage for this post …

One way to differentiate Emerald from Skimmer larvae/exuvia is to examine the anal pyramid: it’s probably Corduliidae (Emeralds) if the cerci are at least half as long as the paraprocts; it’s probably Libellulidae (Skimmers) if the cerci are less than half the length of the paraprocts. More about this in a follow-up blog post. Source Credit: Ventromedial groove, by Walter Sanford.

Here are two examples that illustrate when the method works to confirm exuviae are from Family Libellulidae (Skimmers).

Eastern Amberwing (Perithemis tenera)

Look closely at the full-size version of the following annotated image of an exuvia from an Eastern Amberwing dragonfly (Perithemis tenera).

Notice the cerci are slightly less than half the length of the paraprocts, indicating this specimen is from Family Libellulidae (Skimmers).

Carolina Saddlebags (Tramea carolina)

The next specimen is an exuvia from a Carolina Saddlebags dragonfly (Tramea carolina).

Notice the cerci are slightly less than half the length of the paraprocts, indicating this specimen also is from Family Libellulidae (Skimmers).


Finally, here’s an example that illustrates when the method doesn’t work.

Spot-winged Glider (Pantala hymenaea)

The last specimen is an exuvia from a Spot-winged Glider dragonfly (Pantala hymenaea). Spot-winged Glider is a member of Family Libellulidae (Skimmers).

Notice the cerci are longer than half the length of the paraprocts, suggesting this specimen is from Family Corduliidae (Emeralds). But the exuvia isn’t an Emerald — it’s a Skimmer!

As it turns out, for genus Pantala it’s more important to look at the relative length of the superior abdominal appendage (epiproct) versus the inferior abdominal appendages (paraprocts). Who knew?

What the take-aways?

Although I haven’t identified (with certainty) many species of exuviae from Family Libellulidae (Skimmers), it didn’t take long to find an exception to the rule of thumb for differentiating Emeralds and Skimmers by examining the relative length of cerci versus paraprocts.

In contrast, the rule of thumb that looks at the presence or absence of a ventromedial groove seems to work every time, with the caveat that some species in other families feature a ventromedial groove. In those cases, the family to which the specimen belongs is fairly obvious.

I think it’s good to have more than one arrow in your quiver, so you should be familiar with both methods for differentiating Emeralds and Skimmers. That said, I recommend starting the process of identification by looking for a ventromedial groove.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.


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