Archive for the ‘dragonflies’ Category

Arrowhead Spiketail (terminal appendages)

January 21, 2022

Arrowhead Spiketail dragonflies (Cordulegaster obliqua) were spotted along small streams at undisclosed locations in Fairfax County and Prince William County, Virginia USA.

Male and female Arrowhead Spiketails are similar in appearance. They can be differentiated based upon several field marks.

Male

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

07 JUL 2014 | Fairfax County | Arrowhead Spiketail (male)

Arrowhead male and female cerci are similar in appearance, and it can be challenging to see the epiproct clearly from some viewpoints. When in doubt whether an individual is male or female, look for indentations at the base of the hind wings of males.

07 JUL 2014 | Fairfax County | Arrowhead Spiketail (male)

Female

This individual is a female, as indicated by her rounded hind wings, terminal appendages, and prominent subgenital plate (ovipositor) at the tip of her abdomen.

21 MAY 2019 | PNC. Wm. County | Arrowhead Spiketail (female)

Although Arrowhead male and female cerci are similar in appearance, there is no mistaking the subgenital plate of female spiketails! It’s easy to see why “Spiketails” is the common name for Family Cordulegastridae.

21 MAY 2019 | PNC. Wm. County | Arrowhead Spiketail (female)

So the take-away is simple: If you see a subgenital plate then the individual is definitely female; if not, then it’s probably a male.

Copyright © 2022 Walter Sanford. All rights reserved.

Hunting spiketail dragonflies in Virginia

January 11, 2022

There are three genera in Family Cordulegastridae (Spiketails) worldwide: Anotogaster; Cordulegaster; and Neallogaster. Only Genus Cordulegaster is found in the United States of America.

Four species of Cordulegaster are found in the Commonwealth of Virginia: Brown Spiketail (C. bilineata); Tiger Spiketail (C. erronea); Twin-spotted Spiketail (C. maculata); and Arrowhead Spiketail (C. obliqua).

It’s all about habitat, habitat, habitat.

In the world of odonates, there are habitat generalists and habitat specialists. Spiketail dragonflies are habitat specialists.

Dennis Paulson’s description of the habitat for each species of spiketail found in Virginia is shown in the following list. Notice the list is generic, meaning, specific names are not given. As you read the descriptions, look for commonalities among the habitats.

1. Cordulegaster sp.

Habitat: Small to midsized rocky streams with good current and muddy pools, typically in forest. Occasionally seen patrolling on larger rivers. Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 7058-7059). Princeton University Press. Kindle Edition.

2. Cordulegaster sp.

Habitat: Small woodland streams. Source Credit: Paulson, Dennis. Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Location 7145). Princeton University Press. Kindle Edition.

3. Cordulegaster sp.

Habitat: Small swift streams and soft-bottomed muddy seeps in forest, also streams reduced to series of small pools during drier weather. As in some other spiketails, skunk cabbage often present. Source Credit: Paulson, Dennis. Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 7081-7082). Princeton University Press. Kindle Edition.

4. Cordulegaster sp.

Habitat: Small forest streams and seeps, often with skunk cabbage and interrupted fern. Source Credit: Paulson, Dennis. Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 7028-7029). Princeton University Press. Kindle Edition.

Commonalities

Did you notice the habitats for all four species of spiketails found in Virginia have two characteristics in common?

  • small streams, sometimes seep-fed
  • located in the forest/woodlands

When we say small streams, we mean smallmuch smaller than you might think! Although Twin-spotted Spiketail can be found along mid-size streams (often near the confluence of a smaller stream with a mid-size stream) we think Twin-spotted are more common on small streams.

Answer Key

The following list shows the species of spiketail that matches each of Dennis Paulson’s habitat descriptions.

  1. Twin-spotted Spiketail (Cordulegaster maculata)
  2. Brown Spiketail (Cordulegaster bilineata)
  3. Arrowhead Spiketail (Cordulegaster obliqua)
  4. Tiger Spiketail (Cordulegaster erronea)

The common name for each species is hyperlinked to a page in Walter Sanford’s Photoblog featuring many photographs of that species. The scientific name for each species is linked to Mike Boatwright’s “Spiketails” gallery of photographs on Facebook; click on each photo to see the identity of the spiketail species.

The spiketail species in the preceding lists are shown in chronological order of emergence in Virginia, with Twin-spotted being the earliest and Tiger being the latest. There is some overlap of adult flight periods for some species. Online, interactive Odonate Calendars help you know when to be on the lookout for each species.

I found a small woodland stream. Where should I look for spiketails?

If you’re planning to hunt for spiketails during the 2022 odonate season, the time is now to start scouting small streams in the forest such as the one shown in the following photo.

Photo used with written permission from Mike Boatwright.

Our advice: Focus on finding the right habitat first, rather than finding a particular species of spiketail. Revisit the same small stream(s) periodically throughout the entire odonate season to see which species prefer the stream(s). Be peristent — persistence pays when hunting spiketails!

Twin-spotted Spiketail and Brown Spiketail can be found perching either in fields or along trails located near the small streams from which they emerge. In our experience, Brown Spiketail spends the most time perching of all species of spiketails found in Virginia.

Arrowhead Spiketail and Tiger Spiketail fly long patrols back-and-forth along the stream channel itself, approximately six inches (6″) above the water level. Arrowhead Spiketail stops to perch at the end points of its patrol, often in a sunny clearing or field. On the other hand, we think it’s safe to say Tiger Spiketail perches infrequently.

Do other types of odonates live in the same habitat?

Seeps and small seep-fed streams in the forest are perfect places to look for Gray Petaltail dragonfly (Tachopteryx thoreyi), another habitat specialist found in Virginia, as well as spiketails such as Arrowhead and Tiger.

Photo used with written permission from Mike Boatwright.

Related Resources

Editor’s Note: My good friend and odonate hunting buddy Mike Boatwright and I collaborated to share some of the wisdom gleaned from our experiences hunting spiketail dragonflies in Virginia. Thanks, Mike — couldn’t have done it without you!

Copyright © 2022 Walter Sanford. All rights reserved.

Collecting odonate exuviae

January 7, 2022

Odonates (dragonflies and damselflies) are aquatic insects that 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.

I think it’s safe to say less is known about odonates during the aquatic phase of their lives than during the terrestrial phase. In my opinion, there is a real opportunity to make a significant contribution to the body of scientific knowledge about odonates by collecting and identifying exuviae.

What can be learned from collecting odonate exuviae?

Here are two examples that illustrate why I think it’s important to collect and identify odonate exuviae.

I’ve never seen an adult Arrow Clubtail dragonfly (Stylurus spiniceps). That’s not surprising, since many experienced odonate hunters classify them as uncommon to rare.

But I know a place along the Potomac River in Fairfax County, Virginia USA where I am certain Arrow Clubtail dragonflies live. How do I know? Because I collected a Stylurus spiniceps exuvia from that location on 04 August 2016.

An Arrow Clubtail dragonfly (Stylurus spiniceps) exuvia collected at Riverbend Park, Fairfax County, Virginia USA.

04 AUG 2016 | Fairfax County, VA | Stylurus spiniceps exuvia (ventral)

More recently, my good friend and odonate hunting buddy Mike Boatwright discovered a small breeding population of Zebra Clubtail dragonflies (Stylurus scudderi) at an undisclosed location in Amherst County, Virginia USA. For several years, Mike found exuviae but no adults. On 22 July 2021, years of searching the site finally came to fruition when Mike discovered a teneral female Zebra Clubtail.

13 JUL 2018 | Amherst County, VA | Stylurus scudderi exuvia (dorsal)

Do you need a permit in order to collect odonate exuviae?

A strict interpretation of the Code of Virginia might lead one to think a permit is required.

It is unlawful to collect animal parts, such as feathers, claws, and bones without a permit (4 VAC 15-30-10 and §§ 29.1-521 and 29.1-553). Source Credit: Overview: Collecting, Exhibiting, and Releasing Wildlife, Virginia Department of Wildlife Resources.

That being said, it appears there is an exception for Phylum Arthropoda.

At this time no DWR permit is required for the following: Phylum Arthropoda EXCEPT for the Superfamilies Astacoidea & Parastacoidea (Crayfish) – Arthropoda includes: Insects, arachnids, millipedes, centipedes and other crustaceans (EXCEPT Crayfish) such as: isopods, amphipods etc. … Source Credit: Overview: Collecting, Exhibiting, and Releasing Wildlife, Virginia Department of Wildlife Resources.

I interpret the Code of Virginia to mean a permit IS NOT required to collect odonate exuviae.

How to collect odonate exuviae

Before you collect an exuvia, please photograph the specimen in situ. Record the date, location, and species (if known). A photograph is especially valuable when both the adult and exuvia are shown in the same photograph.

17 JUN 2021 | PNC. Wm. County | Anax junius exuvia (lateral)

Here are my tips for collecting exuviae. Bear in mind, I’m a perfectionist. It’s a fault, but hey, I am what I am and that’s all that I am.

I carry several items in my camera bag: a small plastic spoon; narrow strips of heavy card stock (maybe 3/8″ wide and two inches long); a small pair of scissors (one of three tools in a simple Swiss Army knife); and small plastic containers.

“Go kit” for collecting odonate exuviae.

I’m guessing most people just grab an exuvia with their fingers, but whenever I do that I hear a crunching sound that makes me cringe and parts tend to break off, e.g., legs.

If the exuvia is on a sandy stream bank, then I scoop the specimen with a spoon. If the specimen is clinging to something like a rock or wooden dock, then I slide the handle of the spoon under the body and gently pry it off the surface. Those little grabbers on the end of their legs are very “grippy,” so “gently” is the operative word. If the handle of the spoon won’t fit under the body, that’s when I use the card stock.

If the exuvia is clinging to vegetation, e.g., a cattail, then make the “peace sign” with one hand and insert the stem up to the notch between your pointer- and middle fingers and then close those fingers. Put your hand BELOW the exuvia, palm up, like a cup (in case the specimen falls off the stem). Use scissors to cut the stem below your fingers/hand and a little above the exuvia. Put the specimen in a collecting container, including the stem.

I use large plastic pill bottles. (I take eye vitamins that come in a wide-mouth bottle, perfect for big specimens with long legs such as cruisers and Dragonhunter.) I also use the smallish plastic containers for Philadelphia cream cheese — they can be “nested,” allowing you to carry several containers without taking up much space.

There, now you know more about how to collect odonate exuviae than you ever wanted to know!

What are the take-aways?

Hey, I get it — building a collection of odonate exuviae and learning to identify them might not interest you. But I can assure you there are many people like me who are interested in odonate exuviae who would love to have specimens that you find and collect.

I’m not necessarily saying you should go out hunting specifically for exuviae, but I am saying when you go hunting adult dragonflies and damselflies please be on the lookout for exuviae and collect them when you find them (and I predict you will).

In this way, there is a multiplier effect that will result in the collection of more specimens than a single individual is likely to find. In turn, this should help to advance our understanding of the odonates of Virginia.

Copyright © 2022 Walter Sanford. All rights reserved.

The time is now!

January 4, 2022

Happy New Year! Let the yearning begin. Wait, what? Yep, I’m fighting feeling like I can’t wait for the start of the new odonate hunting season.

Realistically it will be a few months before adult dragonflies and damselflies are flying again, but that’s a good thing. Wait, did I just say that? Yes, and here’s why.

The odonate hunting “off season” provides a good opportunity to plan for the next campaign by making a list of target species and laying out when and where to look for them.

Why is it important to make a plan? Because the season starts slowly but explodes quickly. To illustrate my point, take a look at my Odonate Calendar for adult flight dates of dragonfly species for the month of February (shown below). Not much happening until the end of the month, right?

Dragonflies (VA Flight Dates) | February 2022

Now look at March (shown below). There’s an explosion of species beginning around the second week in March. The boom continues into July before slowing down noticeably in August.

Dragonflies (VA Flight Dates) | March 2022

Also notice many of the spring species of dragonflies are habitat specialists that require extra time and effort to find. So my advice is start planning now for a more productive and satisfying season of odonate hunting.

Related Resources

Both of the following resources feature online, interactive calendars for dragonflies and damselflies based upon Dr. Steve Roble’s excellent datasets for the Commonwealth of Virginia.

Copyright © 2022 Walter Sanford. All rights reserved.

New Life List additions in 2021

December 21, 2021

The anticipation of the hunt and the thrill of discovery — the adrenalin rush from finding new species of odonates is ever more elusive as one gains experience and expertise. Accordingly, the number of additions to my Life List is fewer year after year.

Selys’s Sundragon (Helocordulia selysii)

Selys’ Sundragon dragonfly (Helocordulia selysii) was spotted during a photowalk along a mid-size stream at an undisclosed location in Prince William County, Virginia USA.

This individual is a male with a malformed abdomen. Selys’s Sundragon is a new species for both my Life List of odonates and for Prince William County, VA.

13 APR 2021 | Prince William County, VA | Selys’s Sundragon (male)

Uhler’s Sundragon (Helocordulia uhleri) and Selys’s Sundragon are colocated at many sites — find one species and you should find the other. I’ve been on the lookout for Selys’s since Uhler’s was found several years ago near the site where this Selys’s was spotted.

Yellow-sided Skimmer (Libellula flavida)

Yellow-sided Skimmer dragonflies (Libellula flavida) were spotted around a small pond at an undisclosed location in Prince William County, Virginia USA.

The first individual is a female, as indicated by her terminal appendages.

17 JUN 2021 | PNC. Wm. County | Yellow-sided Skimmer (female)

The last individual is a male, as indicated by his blue coloration and terminal appendages.

17 JUN 2021 | PNC. Wm. County | Yellow-sided Skimmer (male)

Many species of dragonflies in the Family Libellulidae (Skimmers) are habitat generalists and relatively easy to find almost anywhere there is water. In contrast, Yellow-sided Skimmer is a habitat specialist that is challenging to find.

Tiger Spiketail (Cordulegaster erronea)

Tiger Spiketail dragonfly (Cordulegaster erronea) was captured along a small stream at an undisclosed location in Prince William County, Virginia USA. The specimen was photographed and released unharmed.

05 AUG 2021 | Prince William County, VA | Tiger Spiketail (male)

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

05 AUG 2021 | Prince William County, VA | Tiger Spiketail (male)

“Sight records are insufficient” is one of many “Walterisms.” In other words, I don’t add a species to my Life List until I have photographed it. And so it is with Tiger Spiketail. I have seen several Tiger Spiketail dragonflies during the past few years (at several locations) but had no photos to show for my efforts because they are fliers rather than perchers.

Copyright © 2021 Walter Sanford. All rights reserved.

Determining final instar the Cham way

December 14, 2021

Did you notice I added a new text label to the annotated image of an exuvia from a Comet Darner dragonfly (Anax longipes) featured in my last two blog posts? I added the label in order to make the connection between this image and related ideas discussed in two other relatively recent blog posts (See Related Resources, below).

Remember that all dragonflies and damselflies have a 10-segmented abdomen, numbered from front to back. “S4” stands for abdominal segment four.

Counting odonate abdominal segments can be challenging sometimes. A good strategy to avoid mis-numbering is to begin counting abdominal segments from S10 (located toward the posterior end of larvae (nymphs)/exuviae) and work toward the thorax.

Final instar, the Cham way

There is a simpler way to estimate final instar than calculating instar equivalent.

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 at the preceding annotated image. Notice the tips of the wing pads reach the fourth abdominal segment (S4), indicating the dragonfly larva that emerged from this exuvia had reached final instar. And that leads to the other idea I mentioned at the outset of this blog post.

Every odonate exuvia is a cast skin of the larva at F-0, the final instar, before it emerges to become an adult.

Turns out that’s another nugget of gold paraphrased from Steve Cham’s beautiful little book.

Post Update

The beauty of the Cham way of determining final instar is it’s simplicity. That’s the upside. The downside is there’s no way to determine the actual instar when it isn’t F-0.

For example, the following composite image shows dorsal views of a Common Green Darner (Anax junius) nymph (larva) and exuvia. As expected, the exuvia is F-0 because its wing pads cover S4. On the other hand, the nymph is F-? because its wing pads only reach S2.

Image used with written permission from Freda van den Broek.

Photo Credit: Both specimens (shown above) were collected by Freda van den Broek. The nymph was collected on 06 April 2020 from the Milwaukee River in Ozaukee County, Wisconsin USA, photographed, and released unharmed. The exuvia was collected from Ozaukee County too.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Proof of concept, revisited

December 10, 2021

In this blog post I’m going to show you how I used Photopea to annotate one of my photos. The workflow using Photopea is virtually identical to the way I annotate photos using Adobe Photoshop.

The original photo was edited using Apple Aperture (a discontinued photo editor) and Photoshop (for spot removal and sharpening). I could have attempted to edit the photo using Photopea but that wasn’t the point of my “Proof of concept” blog post.

Finished project

The first screen capture shows the finished project — I used it to reverse-engineer the steps that I took to create the annotated image and the settings I made along the way.

The “Layers” panel (located in the right sidebar) shows the finished project is compromised of seven layers, listed from bottom to top in the order they were created.

The “Background” layer is the photo itself. Go to File / Open… and navigate your computer to find a photo you would like to annotate.

View / Rulers

Before proceeding, it’s helpful to turn on “Rulers.” More about that later. In the Photopea menu bar, go to View and check Rulers.

Tech Tips: command-R (macOS) is a keyboard shortcut that can be used to toggle Rulers on/off.

The “View” menu also includes “Zoom In” and “Zoom Out” plus the associated keyboard shortcuts.

Press and hold the spacebar. Notice the arrow-shaped cursor turns into a hand that can be used to drag the canvas around the work space.

Post Update: View / Screen Mode > Fullscreen will scale up the Photopea window to fit the size of your computer screen. Fullscreen mode makes it much easier to work on fine details, especially when used in combination with the “Zoom Tool” and “Hand Tool”; the icon for both tools appears in the lower part of the left sidebar. Try it — you’ll like it! Uncheck “Fullscreen” in order to return to the desktop view. By the way, did you notice I added another guide line and Text layer for a follow-up blog post?

Text Tool settings: Title

The title is the first layer I added using the following selections: IBM Plex Sans (font type); SemiBold (font style); Size = 150 px; Color = Black; and “Aa” = Sharp.

Tech Tips: Text size is measured in pixels, not points. I’m not sure Photopea is calibrated correctly to convert points to pixels. Test it yourself using one of many online points-to-pixels calculators such as PT to PX Converter.

No matter, click the down arrow beside text “Size” and simply use the slider to select a text size that you like. You can also highlight the pixel size and type the exact number you prefer.

To begin adding text to your project, select the “Text Tool” (located in the left sidebar), click an insertion point on the photo and start typing. The default name for the new layer is “Text layer 1, 2, 3, etc.”

When you are finished, either delete the layer by clicking the “Cancel” button (X icon located near the right end of the Photopea menu bar) or save changes made to the layer by clicking the “Confirm” button (checkmark icon located to the right of the X) and the layer name changes so it is the same as the text you typed. In this case, I shortened the name of the layer to “Comet Darner dragonfly.”

With the layer selected, click on the “Move Tool” (left sidebar, at the top) and click-and-drag the text to reposition it exactly where you like.

Text Tool settings: Labels

Next I added a layer for “eye (1 of 2),” one of several labels for parts of the anatomy, using the following selections: IBM Plex Sans (font type); Regular (font style); Size = 100 px; Color = Black; and “Aa” = Sharp.

Tech Tips: The “Sharp” setting is used to avoid text with “jaggies,” that is text with saw tooth edges.

As an aid for aligning text, I created a blue guide line by clicking on the ruler along the top of the screen and dragging down to position the guide line on the photo. The guide line can be repositioned using the “Move Tool.”

Line Tool settings

The next layer I added is an arrow that points from the label to the anatomical part, in this case an eye. The settings I used for “Arrow 1” are shown in the following screen capture.

Tech Tips: Add a new vertical guide line for Arrow 1 by clicking on the ruler along the left side of the screen and dragging to the right to position the guide line on the photo. Right-click on the “Rectangle Tool” and select the “Line Tool.” I used shift-click-and-drag to draw a straight arrow that is aligned with the new blue guide line.

Add more layers

I followed the same steps described above to add a Text layer for “wing pads,” a new guide line for Arrow 2 and an arrow that points from the label to the anatomical part, and another Text layer for “prementum.”

Saving / Exporting

I saved the final image as a Photoshop document by selecting File / Save as PSD. The resulting PSD file can be reopened in Photopea in order to continue working on the project. Post Update: .psd files created by Photopea can be opened in Adobe Photoshop, although it is likely the font(s) you chose to use in Photopea are not available in Photoshop. Photoshop will prompt the user to resolve the problem.

I also saved the file as a PNG by selecting File / Export as.

What are the take-aways?

Open Photopea in a Web browser: www.photopea.com (For what it’s worth, I prefer “Google Chrome.”) Since Photopea is Web-based, it runs on desktop computers, laptop computers, tablets, and smart phones. Having said that, I think it would be challenging to annotate a photo with a tablet or phone unless those devices are used in combination with an external keyboard and mouse. Not impossible, but definitely challenging.

My dear friend Phil Wherry passed away too long ago. Phil was my tech guru for many years. I’m the type of person who suffers from “approach avoidance” — I like to know what will happen BEFORE I do something. One of the best bits of tech advice Phil shared with me is “Don’t be afraid to experiment and see what happens.” That’s exactly what I did when I used Photopea to annotate one of my photos and I encourage you to do likewise. Good luck!

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Proof of concept

December 7, 2021

Can Photopea be used to annotate photographs? Yes!

Do the results look as good as photos of the same subject that were annotated using Adobe Photoshop? You be the judge.

Comet Darner (Anax longipes) | exuvia (lateral)

In my opinion the results are of comparable quality and that’s saying a lot considering this is my first attempt at using Photopea to annotate a photo.

As expected, the workflow flowed slowly since this was the first time I used many of the tools featured in Photopea.

I saved the final image as a Photoshop document by selecting File / Save as PSD. The resulting PSD file can be reopened in Photopea in order to continue working on the project. I also saved the file as a PNG by selecting File / Export as.

The Backstory

The preceding photo shows an exuvia from a Comet Darner dragonfly (Anax longipes) that was collected by Stanley Caveney on 19 July 2021 from a pond at MeadowWoods in West Elgin, Ontario, Canada. Sincere thanks to Stan for kindly sharing this beautiful specimen!

Related Resource: Learn Photopea

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 emerged.

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 Resources

Copyright © 2021 Walter Sanford. All rights reserved.


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