Archive for October, 2021

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 emerges to become an adult. Therefore the instar equivalent 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.

Ventromedial groove

October 15, 2021

In North America (restricted to Canada and the United States of America) there are seven families of dragonflies in the suborder Anisoptera.

Identification of dragonfly larvae (nymphs)/exuviae to the Family Level is fairly straightforward for five of the seven families.

Flat labium

Three families feature a flat labium and are easy to differentiate: Aeshnidae (Darners); Gomphidae (Clubtails); and Petaluridae (Petaltails).

Darner larvae (nymphs)/exuviae have long, thin antennae; Clubtail larvae/exuviae have short, thick antennae. Petaltail larvae/exuviae feature several distinctive field marks that are easy to recognize.

Mask-like labium

Four families feature a mask-like labium: Cordulegastridae (Spiketails); Corduliidae (Emeralds); Libellulidae (Skimmers); and Macromiidae (Cruisers).

Two of these four families are easy to recognize. The distinctive jagged crenulations on the face mask of Spiketails are unmistakeable! Cruisers feature a prominent “horn” on the face-head.

In the opinion of the author, larvae/exuviae from Emeralds and Skimmers can be challenging to differentiate and identify to the family level.

Anal pyramid

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.

Ventromedial groove

Another 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.

For example, look at the full-size version of the following annotated image of a Common Baskettail dragonfly (Epitheca cynosura) exuvia. Notice the groove down the middle of the prementum, oriented vertically in the photo — that’s a “ventromedial groove” (a compound word derived from “ventral” and “medial/midline”) — indicating this specimen probably is from Family Corduliidae (Emeralds).

… the groove is developed on the basal half of the prementum … Source Credit: K. J. Tennessen, Dragonfly Nymphs of North America, https://doi.org/10.1007/978-3-319-97776-8_11, p. 346.

Here’s another example showing a ventromedial groove in the prementum of a Prince Baskettail dragonfly (Epitheca princeps) exuvia.

In contrast, look closely at the full-size version of the following photo of a Spot-winged Glider dragonfly (Pantala hymenaea) exuvia. Notice there is no ventromedial groove in the prementum, indicating this specimen probably is from Family Libellulidae (Skimmers).

An important caveat

Beware: Some larvae/exuviae in other families of dragonflies, such as Tiger Spiketail dragonfly (Cordulegaster erronea), feature a ventromedial groove in the prementum. Therefore the take-away from this post is the presence of a ventromedial groove is not a single definitive morphological character for Emeralds, rather it should be used in combination with other field marks.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Burrowing hooks

October 12, 2021

Odonate nymphs (larvae) can be classified broadly into three (3) groups: Burrowers; Climbers/Clingers; and Sprawlers. Source Credit: “Conservation of Illinois: Dragonflies” Webinar (1:17:19) by Marla Garrison, McHenry County College.

Some species of nymphs (larvae) in Family Gomphidae (Clubtails) are burrowers that have an anatomy adapted for burrowing into sandy substrates quickly, including a torpedo-shaped body and thick legs with burrowing hooks.

Pop Quiz: Using the preceding annotated image as a guide, can you find the burrowing hooks on the front- and middle legs of the following specimen?

Related Resources

The following videos from the Dragonfly Society of the Americas show two species of clubtails burrowing into sand. Thanks to Marla and Carlos Garrison for sharing these videos via YouTube. Both videos are hyperlinked from “The Search Begins” by Marla Garrison and Ken Tennessen (Argia, Volume 33, Issue 3).

Common Sanddragon (Progomphus obscurus)

Riverene Clubtail (Stylurus amnicola)

Copyright © 2021 Walter Sanford. All rights reserved.

Comet Darner exuvia: annotated images

October 8, 2021

My last blog post was a “sketch pad” of test shots of an exuvia from a Comet Darner dragonfly (Anax longipes) collected by Stanley Caveney on 19 July 2021 from a pond at MeadowWoods in West Elgin, Ontario, Canada. All of the shots in that post are unedited JPGs straight from my camera. This post features edited versions of the RAF (raw) files from that photo shoot, including some images with value-added annotations.

Lateral view

I considered annotating the first photo but decided to allow it to stand on its own as the latest addition to my Odonart© Portfolio.

Comet Darner (Anax longipes) | exuvia (lateral)

Ventral view

I used Adobe Photoshop to create a composite image that features the best parts of two photos from the sketch pad.

This specimen is from a male Comet Darner, as indicated by its vestigial primary- and secondary genitalia. The inset photo shows a clear view of the vestigial hamuli (secondary genitalia) that are partially obscured in the background photo.

Comet Darner (Anax longipes) | exuvia (ventral)

Prementum

The last photo shows a closer view of the mentum, a two-segment hinged “jaw” that is used to grab food: the prementum is the segment of the labium closer to the mouth; the postmentum is the segment closer to the base of the head. Only the prementum can be seen in the following photo.

Comet Darner (Anax longipes) | exuvia (prementum)

The preceding annotated image of the prementum includes labels for the moveable hooks (2 of 2) and palpal lobe (1 of 2). Notice that A. longipes palpal lobes are squared off, in contrast with the more rounded shape of the labial palps of Common Green Darner (Anax junius).

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Comet Darner exuvia: photo sketch pad

October 5, 2021

Sometimes I shoot test shots of an odonate exuvia that are used to plan the final shots I have in mind for an identification guide featuring annotated photos.

All of the shots in this post are unedited JPGs straight from my camera, with the exception of the first ventral view (cropped to remove a distracting element from the composition).

Lateral view

I started with a lateral view of an exuvia from a Comet Darner dragonfly (Anax longipes) exuvia collected by Stanley Caveney on 19 July 2021 from a pond at MeadowWoods in West Elgin, Ontario, Canada.

Comet Darner (Anax longipes) | exuvia (lateral)

Ventral view

The next two photos show my frustratingly poor attempts to pose the specimen for shots of the ventral side of the exuvia. Every time I positioned the subject the way I wanted, it rolled over before I could take a shot!

Comet Darner (Anax longipes) | exuvia (ventral)

The two shots combined show the vestigial primary- and secondary genitalia that indicate this specimen is from a male Comet Darner. Yeah, I know it would help to annotate those parts of its anatomy, but that’s the next step. In the meantime, please follow the embedded hyperlink shown above and you might be able to figure out what I’m saying.

Comet Darner (Anax longipes) | exuvia (ventral)

Prementum

The last photo shows a closer view of the prementum. My goal was to get a better look at the labial palps. Again, annotations would help, but if you know what I’m talking about then you can see the palpal lobes are squared off.

Comet Darner (Anax longipes) | exuvia (prementum)

Copyright © 2021 Walter Sanford. All rights reserved.

Mind blown!

October 1, 2021

I don’t know exactly what eBay is today, but I know it was a Den of Thieves where people could go to buy and sell stuff, usually used. And I know several people who were ripped off (lost money) on eBay, both as buyers and sellers. As a result, my mindset toward eBay has been “avoid it like the plague!”

eBay seems to have evolved into an Amazon-like online superstore where you can shop for new stuff as well as buy/sell used stuff. Imagine my surprise when I rolled the dice and ordered a hard-to-find item from a vendor in Japan and the experience turned out to be 99.9% positive. Mind blown!

The Backstory

A long time ago, I bought a “tele conversion lens” and adapter for my Panasonic Lumix DMC-FZ150 superzoom bridge camera. Both accessories were made by Panasonic. Using the tele conversion lens, the actual magnification is 1.7 times the display. For example, at 24x — the maximum zoom magnification of the FZ150 — the actual magnification is ~40x!

When I upgraded to the Panasonic Lumix DMC-FZ300, I wanted to be able to use the same “tele conversion lens.” It was unclear to me whether the DMW-LA5 adapter that works with the FZ150 would fit my FZ300. I was aware that Panasonic also made (past tense) a DMW-LA7 adapter for the Panasonic Lumix DMC-FZ200, but I wasn’t sure the same adapter/lens combo would work with my FZ300.

Impasse Breakthrough

Recently I stumbled across a comment by a Panasonic employee in the Q&A section of an archived product page for the DMW-LA7 adapter (regret I can’t remember where I read the comment) in which the employee clearly stated the adapter is compatible with the FZ300.

Product image courtesy Panasonic Store on Amazon.

Turns out the adapter is no longer made by Panasonic so I started searching online for a place to buy the adapter, new or used. After a lot of fruitless searching, I found several vendors on eBay that sell the adapter. I fully expected the adapter would turn out to be a knock-off of some sort, but hey, it’s essentially just a metal tube with screw threads on both ends so I figured any DMW-LA7 compatible adapter should work. I decided to place an order with a company called “Japan-Excite.”

My order was delivered 10 days later. I was STUNNED when I opened the “parcel” and discovered the adapter is original equipment from Panasonic, in the original box, and apparently new! And I was delighted that it fits perfectly on my FZ300 and with the DMW-LT55 tele conversion lens.

Needs Improvement

So why did I say the experience was 99.9% positive? Because the “parcel” used to ship the product looked like a laminated paper bag of some sort — it reminded me of the brown paper bag lunches my mother used to pack when I was in elementary school. Inside the bag, the item was packed in bubble wrap enclosed by corrugated cardboard folded four times to fit around the bubble wrap (open on both ends). All of that said, the product was delivered in good condition. But I must say that I would NEVER ship merchandise from Japan to the United States (or vice versa) using anything less than a sealed cardboard box with plenty of packing material surrounding all sides of the product.

Summary

Long story short, all’s well that ends well although I can’t help but feel like I was extraordinarily lucky!

In summary, the Panasonic DMW-LT55 tele conversion lens works with either the DMW-LA5 or DMW-LA7 adapter: the DMW-LA5 adapter works with the Panasonic Lumix DMC-FZ150; the DMW-LA7 adapter works with both the Panasonic Lumix DMC-FZ200 and Panasonic Lumix DMC-FZ300.

I’m eager to field test the new adapter with my FZ300 to see whether the tele conversion lens performs as well as it does using my FZ150.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.


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