Archive for the ‘education’ Category

MYN – Clubtail exuvia (possible G. vastus)

February 21, 2020

An odonate exuvia was collected from the concrete boat ramp at Riverbend Park, Fairfax County, Virginia USA. This individual is a member of Family Gomphidae (Clubtails), possibly Cobra Clubtail (Gomphurus vastus).

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

The first photograph was especially challenging to shoot. The camera viewpoint and the beam of light used to backlight the “stage” were at a nearly 90° angle, relative to each other, with the net result that the light level fell below pure white toward the background. The work-around that I used is less than elegant and needs to be refined. Any suggestions?

27 MAY 2017 | Riverbend Park | Clubtail exuvia (face-head-dorsal view)

Although the next photo appeared in my last blog post, this version was rotated slightly for a more pleasing appearance than the last iteration.

27 MAY 2017 | Riverbend Park | Clubtail exuvia (dorsal view)

The last photo is focused on the thorax in order to provide a relatively clear view of the prementum. Notice the specimen has a flat labium that doesn’t cover the face (not mask-like), as shown in the first photo. This field mark indicates the exuvia is from either Family Aeshnidae (Darners) or Family Gomphidae (Clubtails). Other field marks, including club-like antennae and the shape of the body, indicate this individual is a species of clubtail.

27 MAY 2017 | Riverbend Park | Clubtail exuvia (ventral view)

Related Resource: Gomphurus vastus exuvia, an identification guide by Walter Sanford featuring annotated images.

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Cicada exuvia

February 17, 2020

An Annual/Periodical Cicada (Family Cicadidae) exuvia was collected from a wooden kayak rack near the concrete boat ramp at Riverbend Park, Fairfax County, Virginia USA.

The specimen was photographed against a pure white background using the “Meet Your Neighbours” (MYN) technique.

27 MAY 2017 | Riverbend Park | cicada exuvia (face-head-dorsal)

Notice the proboscis between the cicada’s two large front legs, as shown in the preceding photo. I’ve seen zillions of cicada exuviae but never noticed a proboscis. Macro photography. It’s good thing!

27 MAY 2017 | Riverbend Park | cicada exuvia (dorsal view)

27 MAY 2017 | Riverbend Park | cicada exuvia (dorsallateral view)

27 MAY 2017 | Riverbend Park | cicada exuvia (dorsallateral view)

The proboscis is plainly visible in the following photo. (Look between the base of the two front legs.)

27 MAY 2017 | Riverbend Park | cicada exuvia (ventral view)

In situ Photographs

Which photo set do you thinks looks more interesting, the Meet Your Neighbours style photographs or the more traditional style of nature photography? In my opinion, the winner is clear!

Related Resources

What are the take-aways?

Based upon the table of “broods” featured in the Wikipedia page listed under Related Resources, I’m thinking the cicada exuvia that I collected during 2017 is more likely an annual cicada than a periodical cicada. For what it’s worth, no evidence of a mass emergence of cicadas was observed.

Copyright © 2020 Walter Sanford. All rights reserved.

Sexing odonate exuviae (Zygoptera)

February 12, 2020

For some (but not all) species of odonate larvae/exuviae, sex is indicated by either a rudimentary ovipositor (female) or vestigial genitalia (male). These sex organs don’t look exactly the same for all species of damselflies, but their function is identical.

The following photo gallery shows relatively clear examples that illustrate how to sex odonate exuvia in Suborder Zygoptera (Damselflies).

Female (rudimentary ovipositor)

Family Calopterygidae (Broad-winged Damselflies)

(none)

Family Coenagrionidae (Narrow-winged Damselflies)

11 MAR 2017 | Argia sp. | exuvia (female)

Family Lestidae (Spreadwings)

(none)

Male (vestigial genitalia)

Family Calopterygidae (Broad-winged Damselflies)

Family Coenagrionidae (Narrow-winged Damselflies)

(none)

Family Lestidae (Spreadwings)

(none)

Related Resources

Copyright © 2020 Walter Sanford. All rights reserved.

Sexing odonate exuviae (Anisoptera)

February 10, 2020

For some (but not all) species of odonate larvae/exuviae, sex is indicated by either a rudimentary ovipositor (female) or vestigial genitalia (male). These sex organs don’t look exactly the same for all species of dragonflies, but their function is identical.

The following photo gallery shows relatively clear examples that illustrate how to sex odonate exuvia in Suborder Anisoptera (Dragonflies).

Female (rudimentary ovipositor)

Family Aeshnidae (Darners)

10 DEC 2018 | Hairy Dragonfly (Brachytron pratense) | exuvia (female)

Family Cordulegastridae (Spiketails)

Family Corduliidae (Emeralds)

(none)

Family Gomphidae (Clubtails)

20 MAR 2018 | Brook Snaketail (Ophiogomphus aspersus) | exuvia (female)

Family Libellulidae (Skimmers)

(none)

Family Macromiidae (Cruisers)

(none)

Family Petaluridae (Petaltails)

Male (vestigial genitalia)

Male odonates have two sets of sex organs: primary genitalia located on abdominal segment nine (S9); and secondary genitalia located on abdominal segments two-to-three (S2-3).

Both sets of vestigial genitalia are clearly visible on the ventral side of some (but not all) specimens, such as the A. umbrosa exuvia shown below.

Family Aeshnidae (Darners)

Family Cordulegastridae (Spiketails)

(none)

Family Corduliidae (Emeralds)

Family Gomphidae (Clubtails)

26 MAR 2018 | Appalachian Snaketail (Ophiogomphus incurvatus) | exuvia (male)

Family Libellulidae (Skimmers)

Family Macromiidae (Cruisers)

Family Petaluridae (Petaltails)

(none)

Related Resources

Copyright © 2020 Walter Sanford. All rights reserved.

Skunk cabbage flowers

February 5, 2020

The following photo gallery shows skunk cabbage (Symplocarpus foetidus) flowers in a forest seep located at Occoquan Regional Park (ORP), Fairfax County, Virginia USA.

This is ideal habitat for Gray Petaltail dragonfly (Tachopteryx thoreyi) larvae, and in fact, numerous adult “Grays” have been observed along a sunny trail near this location. Seeps are home for some species of larvae from Family Cordulegastridae (Spiketails) as well.

03 FEB 2020 | ORP | forest seep, with skunk cabbage flowers

03 FEB 2020 | ORP | forest seep, with skunk cabbage flowers

03 FEB 2020 | ORP | forest seep, with skunk cabbage flowers

03 FEB 2020 | ORP | forest seep, with skunk cabbage flowers

The last photo shows the same location during early Summer 2019. The plant with broad green leaves is skunk cabbage.

01 JUN 2019 | ORP | forest seep, with skunk cabbage

The following quote is perhaps the best description of a forest seep that I’ve read.

[Some] small tributaries … have their sources in numerous woodland seeps. While a few of these perennial springs bubble up out of the ground, most arise in moist hillside patches with lots of decaying leaf litter and luxuriant stands of skunk cabbage. Source Credit: White, Harold B., III. Natural History of Delmarva Dragonflies and Damselflies (Cultural Studies of Delaware and the Eastern Shore) (Kindle Locations 1213-1215). University Press Copublishing Division. Kindle Edition.

Related Resource: Skunk Cabbage: First Flower of the Year… by Alonso Abugattas, Capital Naturalist blog. The blog post includes an embedded link to an informative video by Mr. Abugattas: Capital Naturalist: Skunk Cabbage Blooming (3:58).

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Tramea sp. exuvia (ventral)

February 3, 2020

An odonate exuvia, collected by Andy Davidson near Richmond, Virginia USA, was photographed against a pure white background using the “Meet Your Neighbours” (MYN) technique. Two photos were used to create a composite image: one photo focused on the prementum; and another photo focused on abdominal segment eight (S8).

This individual is from the Genus Tramea (Saddlebags), in the Family Libellulidae (Skimmers). Since it’s nearly impossible to differentiate exuviae from the Genus Tramea to the species level, we’ll leave its identity as Tramea sp. It’s the same specimen featured in my last three blog posts: MYN – Tramea sp. exuvia (face-head-dorsal)MYN – Tramea sp. exuvia (dorsal); MYN – Tramea sp. exuvia (dorsal-lateral).

Tech Tips

The subject was photographed against a pure white background using the “Meet Your Neighbours” (MYN) technique. The exuvia was “staged” on a clear plastic surface raised ~1.5 in (~3.81 cm) above the white background.

The dorsal side of the specimen was lying on the clear plastic. The “eyes” were closer to the light source than all other photos/composite images in a four-part series of this subject; as a result, the eyes look washed out. I know from experience that problem can be solved by moving the clear plastic stage farther from the white background.

In this case, I was less concerned about showing the eyes in their best light and more concerned about looking for signs of sex organs that indicate gender. I don’t see anything that looks like either vestigial genitalia (male) or a rudimentary ovipositor (female).

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.

Pop quiz: Sex the exuvia

January 10, 2020

An odonate exuvia was photographed against a pure white background using the “Meet Your Neighbours” (MYN) technique.

This specimen is a Shadow Darner dragonfly (Aeshna umbrosa) exuvia, collected and identified by Andy Davidson near Richmond, Virginia USA. Shadow Darner is a member of Family Aeshnidae (Darners).

Can you tell whether the exuvia is from a female or male larva? (Hint: The Related Resource, shown below, might be a helpful reference.)

Related Resource: Post update: Aeshna umbrosa exuvia.

Copyright © 2020 Walter Sanford. All rights reserved.

Post update: Aeshna umbrosa exuvia

January 8, 2020

Male odonates have two sets of sex organs: primary genitalia located on abdominal segment nine (S9); and secondary genitalia located on abdominal segments two-to-three (S2-3).

Closer examination of some test shots of the following Shadow Darner dragonfly (Aeshna umbrosa) exuvia, photographed on 02 December 2018, showed both sets of vestigial genitalia are clearly visible on the ventral side of this specimen.

Aeshna umbrosa (mating pair)

All odonates (dragonflies and damselflies) have a 10-segmented abdomen, numbered from front to back. Male dragonfly secondary genitalia, called hamules, are located in segments two and three (S2 and S3); female genitalia in segment eight (S8). Male and female dragonflies form the mating wheel in order for their genitalia to connect during copulation.

A. umbrosa (in wheel). Photo used with permission from Patrick Boez.

Related Resource: Test shots: Aeshna umbrosa exuvia.

Copyright © 2020 Walter Sanford. All rights reserved.

MYN – Hagenius brevistylus exuvia (ventral)

January 6, 2020

An odonate exuvia was photographed against a pure white background using the “Meet Your Neighbours” (MYN) technique.

This specimen is a Dragonhunter dragonfly (Hagenius brevistylus) exuvia. Dragonhunter is a member of Family Gomphidae (Clubtails).

Dorsal view update

I’ve made the same mistake twice recently: When in doubt, the “model” should face the camera! In my opinion, the following updated photo looks better than the version that shows the model facing away from the camera (published in my last blog post).

Ventral view

This individual is a female, as indicated by the rudimentary ovipositor located along the boundary between abdominal segments eight and nine (S8-9).

Related Resources

Tech Tips

The first two photos were taken using the same MYN Field Studio setup described in detail in my last blog post.

The last photo was taken by swapping the Godox TT685F fill flash for my Canon MT-26EX-RT Macro Twin Lite. The Canon flash was set for a power ratio of 1/32.

Copyright © 2020 Walter Sanford. All rights reserved.


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