Posts Tagged ‘exuviae’

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.

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.

Anax junius versus Anax longipes

September 10, 2021

The following photograph shows the relative size of odonate exuviae from two species in the Genus Anax: junius; and longipes. Both specimens are from the Family Aeshnidae (Darners).

Relative size of exuviae from Anax junius versus Anax longipes.

The Common Green Darner dragonfly (Anax junius) exuvia was collected on 17 June 2021 from a small pond at an undisclosed location in Prince William County, Virginia USA.

The Comet Darner dragonfly (Anax longipes) exuvia was collected by Stanley Caveney on 19 July 2021 from a pond at MeadowWoods in West Elgin, Ontario, Canada.

Taxonomy

There are five species of dragonflies in the Genus Anax for the United States and Canada: Amazon Darner (Anax amazili); Common Green Darner (Anax junius); Comet Darner (Anax longipes); Giant Darner (Anax walsinghami); and Blue-spotted Comet (Anax concolor).

Common Green Darner and Comet Darner are the only species from the Genus Anax found where I live in Northern Virginia USA.

Related Resources

Copyright © 2021 Walter Sanford. All rights reserved.

Comet Darner dragonfly (exuvia)

August 27, 2021

An odonate exuvia from a Comet Darner dragonfly (Anax longipes) was collected by Stanley Caveney on 19 July 2021 at MeadowWoods in West Elgin, Ontario, Canada.

This specimen is from Family Aeshnidae (Darners), as indicated by the following field marks: the exuvia has a flat labium that doesn’t cover the face (not mask-like); the antennae are thin and thread-like (not club-like, as in Gomphidae larvae/exuviae); and the eyes are large relative to the size of the head.

19 JUL 2021 | Ontario, Canada | Comet Darner exuvia (lateral view)

Lateral spines along abdominal segments seven, eight, and nine (S7-9) indicate the genus is Anax; the length of the exuvia indicates longipes (~6 cm, measured as is).

The Backstory

Stanley Caveney is shown in the first of several photos taken by Hugh Casbourn. Stan contacted me for confirmation of his tentative identification of several Comet Darner exuviae that he collected during July 2021. Stan kindly gave one of the exuviae to me.

Photo used with written permission from Hugh Casbourn.

I asked Stan whether he had taken photographs of the Comet Darner exuviae in situ. Stan hadn’t, so he and Hugh revisited a local pond where they searched for and found two more exuviae.

How many exuviae do you see in the next photo? Look closely — both cast skins are shown in the same image.

Photo used with written permission from Hugh Casbourn.

An exuvia from a female Comet Darner appears in the foreground of the preceding photograph…

Photo used with written permission from Hugh Casbourn.

and a male Comet Darner appears in the background.

Photo used with written permission from Hugh Casbourn.

I asked Stan for advice regarding where to look for Comet Darner exuviae.

The six exuviae found to date were mainly at the inner edge of the cattail beds, facing the open water of the pond and where the individual cattail plants were spaced out. Source Credit: Personal communication from Stanley Caveney.

Related Resource: Identification Keys to Northeastern Anisoptera Larvae, compiled by Ken Soltesz. Refer to pp. 21-22.

Editor’s Note: Sincere thanks to Derek Caveney, Stan’s son, for shipping the exuvia to me. The specimen was packed so carefully that it arrived in excellent condition, as you can see in the first photo in this blog post. I’m looking forward to shooting a complete photo set of the exuvia.

Copyright © 2021 Walter Sanford. All rights reserved.

Post update: Stylurus sp. exuvia

July 27, 2021

Three years ago I had the honor and pleasure of helping Michael Boatwright, my good friend and odonate hunting buddy, identify an interesting exuvia that he collected on 13 July 2018 at an undisclosed location in Amherst County, Virginia USA.

After working through several dichotomous keys for the identification of odonate larvae/exuviae, Mike and I determined the specimen is most likely from Zebra Clubtail (Stylurus scudderi). Zebra Clubtail is extremely rare in the state of Virginia.

The following annotated image shows a dorsal view of the exuvia.

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

The best way to confirm our tentative identification of the exuvia is to find adult Zebra Clubtail at the same location. Easier said than done! During the next few years, Mike found more 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, shown below.

Photo used with written permission from Mike Boatwright.

Look closely at the full-size version of the preceding photo. Notice the teneral dragonfly is perched on the exuvia from which it emerged. Mike collected the exuvia after the dragonfly flew high into the tree canopy, so now we have the type specimen for verification of other exuviae.

Persistence pays

Sincere congratulations, Mike! You never gave up when it would have been the easier thing to do.

Related Resources

  • Stylurus sp. exuvia – a blog post by Walter Sanford providing a detailed account of the process used to determine the identity of the specimen collected by Mike on 13 July 2018.
  • Mike’s post in the Virginia Odonata Facebook group announcing his discovery on 22 July 2021. Mike is the founder and administrator of Virginia Odonata.

Copyright © 2021 Walter Sanford. All rights reserved.

Common Green Darner dragonfly (external female reproductive anatomy)

June 5, 2020

For some species of odonate exuviae, sex is indicated by a form of remnant reproductive anatomy. These external structures don’t look exactly the same for all species of dragonflies and damselflies, but their function is identical.

As far as I know, this is true for all species in the Family Aeshnidae (Darners) such as Common Green Darner dragonfly (Anax junius).

The following photograph shows a ventral view of a female Common Green Darner dragonfly. Notice the external reproductive anatomical structure on abdominal segment nine (S9) is virtually identical to the remnant anatomical structure on S9 of the exuvia, shown above.

Original photo used with permission from Louisa C. Craven.

The Backstory

My dear friend Louisa Craven discovered the lifeless adult dragonfly while on vacation with her family in Nags Head, North Carolina USA. Louisa is an accomplished wildlife photographer who developed an interest in odonates as a result of many photowalks with me.

Related Resources

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.

Tramea carolina exuvia

January 22, 2020

I’m a man on a mission to demystify identification of odonate exuviae, as I’m fond of saying. Easier said than done. In my experience, the process of identification can be challenging at best and impossible at worst.

For example, it’s nearly impossible to differentiate exuviae from the Genus Tramea (Saddlebags) to the species level.

The search for reliable larval characters to distinguish species of Tramea has generated considerable confusion in the literature. Source Credit: Landwer, Brett & Sites, Robert. (2006). Diagnostic efficacy of morphological characters of larval Tramea lacerata Hagen and Tramea onusta Hagen (Odonata: Libellulidae). Great Lakes Entomologist. 38. 155-163.

More recently, Tennessen cited the preceding research as well as a follow-up article by the same authors in 2010, and wrote…

…specific identification is still problematic. Source Credit: Tennessen, Kenneth. (2019). Dragonfly Nymphs of North America – An Identification Guide. Springer International Publishing. 567.

The fact of the matter is the most reliable way to identify odonate larvae to the species level is to rear them to maturity and emergence, that is, unless you’re fortunate to find a larva emerging in the field. Since an exuvia is essentially a nearly perfect shell of the last instar, it can be used to identify other specimens of the same species by pattern matching.

Rearing an unknown species of larva from genus Tramea

A larva from the Genus Tramea (Saddlebags) was collected by Andy Davidson near Richmond, Virginia USA, and reared to maturity. The following photo shows the adult dragonfly soon after emergence.

Photo used with permission from Andy Davidson.

The image was rotated in order to get a better look at the shape of the “saddlebags” on the rear wings of the dragonfly.

Photo used with permission from Andy Davidson.

The following composite image — created by Ed Lam, author and illustrator of Damselflies of the Northeast — clearly shows the difference in the shape of the saddlebags for Carolina- versus Red Saddlebags. Look closely at the saddlebags in the full-size version of the preceding photo and you can see the pattern perfectly matches the Carolina Saddlebags in Ed’s image, shown below.

Composite image used with permission from Ed Lam.

Look-alikes: Genus Pantala and Genus Tramea

Two genera from the Family Libellulidae (Skimmers) look similar: Genus Pantala (Rainpool Gliders); and Genus Tramea (Saddlebags). If you find an exuvia with long “tail fins,” then it might be a member of one of these two genera.

A Spot-winged Glider dragonfly (Pantala hymenaea) exuvia was collected by Andy Davidson near Richmond, Virginia USA.

A Carolina Saddlebags dragonfly (Tramea carolina) larva was collected by Andy Davidson near Richmond, Virginia USA, and reared to maturity. Andy saved the exuvia after emergence.

The following couplet from Identification Keys to Northeastern Anisoptera Larvae, compiled by Ken Soltesz, can be used to differentiate exuvia from Genus Pantala and Genus Tramea.

p. 37, Key to the Genera of the Family Libellulidae
12a – Superior abdominal appendage (epiproct) as long as, or longer than inferiors [paraprocts]. Pantala
12b – Superior abdominal appendage (epiproct) shorter than inferiors [paraprocts]. Tramea

What are the take-aways?

If you find an exuvia from the genus Tramea, then you might be unable to identify it to the species level.

I collected a Tramea sp. exuvia during Fall 2016 from a water retention pond located at a small park in Fairfax County, Virginia USA. I keyed out the specimen and identified it as Tramea carolina, in part, because Carolina Saddlebags had been observed in numbers at the same location. Am I certain of the identity? Yes and no. I’m certain the specimen is from genus Tramea; I’m reasonably sure (but not certain) it’s T. carolina. That said, my rationale is fairly good.

Related Resources

Copyright © 2020 Walter Sanford. All rights reserved.

“Odonate Larvae and Exuviae” Facebook group

November 29, 2019

I created a new Facebook group called “Odonate Larvae and Exuviae.” Readers of this blog who enjoy my photographs of odonate exuviae might be interested in following the new group. Please join us!

Copyright © 2019 Walter Sanford. All rights reserved.

Odonate exuviae collecting sites

July 29, 2019

The following video shows a “boater’s-eye view” of some sites where odonate exuviae have been collected by Joseph Johnston along Aquia Creek, located in Stafford County, Virginia USA. Joe 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.

The first photo gallery features still images of several spots shown in the preceding video. Joe estimates the water is ~5-6 feet deep outside the channel markers, and much deeper in the middle of the creek.

Joe’s boat is somewhere between the long boat docks (lower-right quadrant) and Government Island (near center), as shown in an aerial view of Aquia Creek provided by Google Maps.

The last photo gallery features still images of several exuviae, shown in situ before Joe collected the specimens. The first photo shows where it all began, when Joe collected his first dragonfly exuvia for me on 20 June 2018.

Related Resources

Credits

All media Copyright © 2019 by Joseph Johnston. Used with permission from Mr. Johnston.

Copyright © 2019 Walter Sanford. All rights reserved.


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