Posts Tagged ‘exuviae’

Epitheca cynosura exuvia

April 26, 2017

On 13 April 2017, a late-stage emergent teneral female Common Baskettail dragonfly (Epitheca cynosura) was observed at Painted Turtle Pond during a photowalk around Occoquan Bay National Wildlife Refuge, Prince William County, Virginia USA.

Several dragonfly exuviae were collected near the same location as the emergent teneral female. All of the exuviae look identical, although there is some variation in size. A two-step process was used to verify the genus and species for one of the larger exuvia.

  • Determine the family.
  • Determine the genus and species.

This specimen is approximately 22 mm (~0.87 in) in length.

Step 1. Family

First, determine the family of the specimen. For reference, watch the excellent Vimeo video, Identifying dragonfly larva to family (8:06). Here’s the decision tree used to identify the exuvia as a member of the Family Corduliidae (Emeralds).

  • The specimen has a mask-like labium that covers the face, characteristic of four families: Cordulegastridae (Spiketails); Corduliidae (Emeralds); Libellulidae (Skimmers); and Macromiidae (Cruisers).
  • There is no horn on top of the face-head, characteristic of Macromiidae, so it’s not a cruiser.
  • Cordulegastridae has jagged crenulations on its labium, so it’s not a spiketail. The crenulations for Corduliidae and Libellulidae look similar.
  • Look at the anal pyramid to differentiate Corduliidae and Libellulidae [See Photo No. 7.]: It’s probably Corduliidae if the cerci are at least half as long as the paraprocts. [Editor’s Note: It’s probably Libellulidae if the cerci are less than half the length of the paraprocts.]

In summary, the exuvia has a mask-like labium with relatively smooth crenulations, no horn on its face-head, and the cerci are more than half as long as the paraprocts, confirming that the specimen is a member of Family Corduliidae (Emeralds).

(See a full-size version of the original photo, without annotation.)

Notice that dorsal hooks are present and well developed on most abdominal segments.

No. 4 | Common Baskettail (Epitheca cynosura) | exuvia (dorso-lateral)

A lateral view of the exuvia provides a good look at the labium, also known as 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.

The white filaments that extend from the split in the thorax (as shown in Photo No. 1-7) are breathing tubes, artifacts of the unique respiratory system of dragonfly nymphs.

(See a full-size version of the original photo, without annotation.)

A closer view of the head shows two “bumps” that may be a pair of tubercles.

Step 2. Genus and species

Characters from Identification Keys to Northeastern Anisoptera Larvae, dichotomous keys compiled by Ken Soltesz, were used to identify the genus and species for the exuvia. Although palpal/mental setae were not examined, all other characters match Epitheca cynosura.

dichotomous key: a key for the identification of organisms based on a series of choices between alternative characters. Source Credit: Merriam-Webster Dictionary.

Alternate Key to the Genera of the Family Corduliidae, p. 29.

Key to the species of the genus (subgenus) Tetragoneuria, p. 32.

No. 7 | Common Baskettail (Epitheca cynosura) | exuvia (anal pyramid)

(See a full-size version of the original photo, without annotation.)

The last photo shows a ventral view of the exuvia. The vestigial hamuli located between abdominal segments two and three (S2-3) strongly suggests this individual is a male, therefore this specimen probably is not the same exuvia from which the teneral female emerged.

(See a full-size version of the original photo, without annotation.)

Tech Tips:

The following equipment was used to shoot all of the preceding photographs: Canon EOS 5D Mark II digital camera, in manual mode; Canon EF100mm f/2.8L Macro lens (set for manual focus) plus a Kenko 20mm macro automatic extension tube; Canon 580EX II external flash tethered to the camera by a coiled six-foot Vello Off-Camera TTL Flash Cord for Canon Cameras, off-camera, in manual mode; the Canon flash optically triggered a small Nissin i40 external flash (in SF mode) used for backlight; and a Sunpak LED-160 Video Light with a white translucent plastic filter used for side light.

Adobe Photoshop CC 2017 was used to annotate selected images.

Related Resources:

Editor’s Note: Sincere thanks to Sue Gregoire, Kestrel Haven Migration Observatory, for verifying my tentative identification, and for sharing some good odonate nymph knowledge regarding vestigial hamuli!

Copyright © 2017 Walter Sanford. All rights reserved.

Late-stage emergent baskettail dragonfly

April 18, 2017

Common Baskettail dragonfly (Epitheca cynosura) was spotted at Painted Turtle Pond during a photowalk around Occoquan Bay National Wildlife Refuge (OBNWR), Prince William County, Virginia USA. This individual is a late-stage emergent teneral female.

I photographed the process of emergence from the first sighting to the time when the teneral dragonfly flew away: I shot 23 photos in approximately 16 minutes; time is compressed by showcasing six (6) select photos taken at major milestones during the event.

The following photo is the first image from a time-series documenting the emergence of the teneral female. Elapsed time is expressed in hh:mm:ss format, e.g., 00:00:00 is the time when I spotted the emergent teneral female, and 00:16:08 is the total elapsed time.

13 APR 2016 | 11:38:41 am EDT | Elapsed time: 00:00:00

Notice the drop of fluid at the tip of the abdomen. Emerging dragonflies pump fluid into their wings, causing the wings to expand. Next, the same fluid is withdrawn from the wings and used to expand the abdomen. Excess fluid is expelled afterward.

13 APR 2016 | 11:40:48 am EDT | Elapsed time: 00:02:07

The next photo shows the first time the wings opened.

13 APR 2016 | 11:48:55 am EDT | Elapsed time: 00:10:14

Then the wings closed again and remained closed for a while.

13 APR 2016 | 11:51:02 am EDT | Elapsed time: 00:12:21

The wings reopened a few minutes later. Notice that several wings are malformed slightly.

13 APR 2016 | 11:54:14 am EDT | Elapsed time: 00:15:33

Finally, the wings open up, and very soon the teneral adult flies away. Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 468). Princeton University Press. Kindle Edition.

The teneral female dragonfly flew away immediately after the last photo in the time-series.

13 APR 2016 | 11:54:46 am EDT | Elapsed time: 00:16:08

This individual is a female, as indicated by her cerci (superior appendages) and thick abdomen. Common Baskettail females have shorter cerci and a thicker abdomen than males of the same species.

Exuviae (in situ)

Several dragonfly exuviae were spotted at Painted Turtle Pond. The exuviae were identified using a dichotomous key for dragonfly larvae; they are cast skins from Common Baskettail.

13 APR 2017 | OBNWR | Common Baskettail (exuvia)

These exuviae are not the one from which the teneral female featured in this post emerged.

13 APR 2017 | OBNWR | Common Baskettail (exuvia)

Copyright © 2017 Walter Sanford. All rights reserved.

Perithemis tenera exuviae

December 6, 2016

Several unknown dragonfly exuviae were collected on 07 July 2016 from the Potomac River, Fairfax County, Virginia USA; two of the specimens are featured in this post. A two-step process was used to identify the genus and species of the specimens.

Family

First, determine the family of the specimens. For reference, watch the excellent Vimeo video, Identifying dragonfly larva to family (8:06).

The exuviae have a mask-like labium (not flat) with smooth crenulations, indicating these individuals are members of Family Libellulidae (Skimmers).

Genus and species

A dichotomous key was used to tentatively identify the exuviae as Eastern Amberwing dragonfly (Perithemis tenera), as indicated by the following morphological characteristics.

  • The cerci (sing. cercus) are slightly less than half the length of the paraprocts.
  • Dorsal hooks are clearly visible on abdominal segments four through nine (S4-9), plus a “nub” that is visible on segment three (S3).
  • Lateral spines are clearly visible on abdominal segments eight and nine (S8-9).

These specimens are the first odonate exuviae that I was able to identify to the species level. Sincere thanks to Sue Gregoire, Kestrel Haven Migration Observatory, for verifying my preliminary observations and tentative identification.

No. 1

Each specimen is approximately 1.4 cm (~0.6″) in length and approximately 0.6 cm (~0.2″) in maximum width. In Photo No. 1, the specimen shown on the left is an emergent nymph that was stuck in its exuvia.

A pair of Eastern Amberwing dragonfly (Perithemis tenera) exuviae collected from the Potomac River, Dyke Marsh Wildlife Preserve, Fairfax County, Virginia USA.

No. 1 | Eastern Amberwing (Perithemis tenera) | exuviae (lateral, dorsal)

(See a full-size version of the original photo, without annotation.)

The white filaments that extend from the split in the thorax (as shown in Photo No. 1-3) are breathing tubes, artifacts of the unique respiratory system of dragonfly nymphs.

No. 2

An Eastern Amberwing dragonfly (Perithemis tenera) exuvia collected from the Potomac River, Dyke Marsh Wildlife Preserve, Fairfax County, Virginia USA.

No. 2 | Eastern Amberwing (Perithemis tenera) | exuviae (dorsal)

No. 3

The eyes are relatively small and widely separated. Notice the mask-like labium (sometimes referred to as “spoon-shaped”) with smooth crenulations along the margins between two lateral lobes.

An Eastern Amberwing dragonfly (Perithemis tenera) exuvia collected from the Potomac River, Dyke Marsh Wildlife Preserve, Fairfax County, Virginia USA.

No. 3 | Eastern Amberwing (Perithemis tenera) | exuviae (head-on)

(See a full-size version of the original photo, without annotation.)

No. 4

One of the keys to identifying skimmer dragonflies to the species level is to carefully examine the anal pyramid (see S10, shown below), including the cerci (sing. cercus) and paraprocts. Notice the cerci are slightly less than half the length of the paraprocts.

An Eastern Amberwing dragonfly (Perithemis tenera) exuvia collected from the Potomac River, Dyke Marsh Wildlife Preserve, Fairfax County, Virginia USA.

No. 4 | Eastern Amberwing (Perithemis tenera) | exuviae (anal pyramid)

(See a full-size version of the original photo, without annotation.)

Tech Tips:

The following equipment was used to shoot the preceding photographs:

Adobe Photoshop CC 2017 was used to annotate selected images.

Related Resources:

dichotomous key: a key for the identification of organisms based on a series of choices between alternative characters. Source Credit: Merriam-Webster Dictionary.

Assuming the convention of labeling the two branches of each dichotomy as “a” and “b”, e.g. 1a, 1b, etc., a list of branches in the decision tree that I used to identify the species of the dragonfly exuviae is as follows: 1b; 4b; 5a; 6a BINGO!

In long form, the decision tree is as follows:

p. 36, Key to the Genera of the Family Libellulidae
1b – Eyes lower, more broadly rounded and more lateral in position; abdomen usually ending more bluntly. [Go to] 4
4b – These appendages [inferior abdominal appendages (paraprocts)] straight or nearly so. [Go to] 5
5a – Dorsal hooks on some abdominal segments. [Go to] 6
6a – Dorsal hook on 9. Perithemis (One species, Perithemis tenera.) BINGO!

Copyright © 2016 Walter Sanford. All rights reserved.

Identifying dragonfly larvae to family

April 7, 2016

A couple of odonate exuviae were spotted in the bioswale (when it still retained water) at the head-end of the Hike-Bike Trail, Huntley Meadows Park. Both specimens are dragonfly exuvia, slightly less than 3/4″ long. I shot some quick-and-dirty still photos of the pair, as well as two sets of macro photos focusing on key anatomical parts.

Then I watched (and transcribed) the instructional video “Identifying dragonfly larva to family.” Be forewarned: Although the identification process is vocabulary-rich, the prerequisite terminology is well-illustrated in the video. Here’s the decision tree I used to make a tentative identification of the family.

Turns out I was correct — the exuviae are members of the Family Libellulidae (Skimmers)! Thanks to aquatic entomologist Celeste Searles Mazzacano, Ph.D., for verifying my tentative identification. The next (bigger) challenge: Learn how to identify odonate exuviae to the genus and species level.

A couple of odonate exuviae spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

ISO 800| 400mm (600mm, 35mm equivalent) | 0 ev | f/11 | 1/250s

The first two photos were taken using a Fujifilm X-T1 digital camera and Fujinon XF100-400mm telephoto zoom lens set for 400mm.

A couple of odonate exuviae spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

ISO 800| 400mm (600mm, 35mm equivalent) | 0 ev | f/11 | 1/250s

The next set of photos was taken using a Raynox DCR-250 close-up filter with my tripod-mounted Panasonic Lumix DMC-FZ150 superzoom digital camera; the scene was lighted using the built-in pop-up flash and Nissin i40 external flash (off-camera, in video mode).

A couple of odonate exuviae spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

ISO 100| 28mm (155mm, 35mm equivalent) | -1.3 ev | f/7.1 | 1/3s

A couple of odonate exuviae spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

ISO 100| 28mm (155mm, 35mm equivalent) | -1.3 ev | f/7.1 | 1/160s

The following photo is my favorite in this subset.

A couple of odonate exuviae spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

ISO 100| 57mm (318mm, 35mm equivalent) | -1.3 ev | f/7.1 | 1/250s

Notice the teeth on the margins of the labium are relatively smooth.

A couple of odonate exuviae spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

ISO 100| 55mm (304mm, 35mm equivalent) | -1.3 ev | f/7.1 | 1/250s

The last set of photos was taken using a Raynox DCR-250 close-up filter with my tripod-mounted Panasonic Lumix DMC-FZ150 superzoom digital camera; the scene was lighted using an off-camera Sunpak LED-160 Video Light (with a white translucent plastic filter) and Nissin i40 external flash (off-camera, in video mode).

A couple of odonate exuviae spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

ISO 100| 56mm (311mm, 35mm equivalent) | -1 ev | f/7.1 | 1/10s

A couple of odonate exuviae spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

ISO 100| 57mm (318mm, 35mm equivalent) | -1 ev | f/7.1 | 1/8s

The following photo is my favorite in this subset.

A couple of odonate exuviae spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

ISO 100| 30mm (164mm, 35mm equivalent) | -1 ev | f/7.1 | 1/6s

The last two shots are close-ups of the anal pyramid. Notice the cerci are less than half the length of paraprocts.

A couple of odonate exuviae spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

ISO 100| 28mm (158mm, 35mm equivalent) | -1 ev | f/7.1 | 1/8s

A couple of odonate exuviae spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

ISO 100| 56mm (311mm, 35mm equivalent) | -1 ev | f/7.1 | 1/8s

Related Resources:

Copyright © 2016 Walter Sanford. All rights reserved.

Odonate exuviae (in situ)

September 12, 2015

Odonates are aquatic insects that spend most of their life as larvae 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.

Careful and/or lucky observers will notice exuviae (sing. exuvia), also known as either “cast skins” or “shed skins,” left behind when odonate larvae emerge.

The first three photographs show exuviae of odonates that emerged from the bioswale at the head-end of the Hike-Bike Trail at Huntley Meadows Park.

The flash/no-flash debate is settled in my mind, as evidenced by the preceding two-image gallery of photos. Although the photo shown on the left may have a more natural or “artier” look, critical detail is lost in the shadows, including the Long-jawed Orb Weaver (Family Tetragnathidae) lurking in the darkness on the left-most cattail rush!

The next photo shows cast skins from two different species of odonates. Most experts agree it is virtually impossible to identify exuviae to the species level using only photographs, although some cast skins are so distinctive it is possible to identify the family from a photo.

Two odonate exuviae (genus/species unknown) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. These individuals emerged from the bioswale at the head-end of the Hike-Bike Trail.

05 AUG 2015 | HMP | two odonate exuviae (genus/species unknown)

The last photograph shows a cast skin spotted in the central wetland area, near beginning of boardwalk.

An odonate exuvia (genus/species unknown) spotted at Huntley Meadows Park, Fairfax County, Virginia USA.

21 AUG 2015 | HMP | odonate exuvia (genus/species unknown)

Related Resources: Be forewarned — identification of odonate larvae is difficult at best and impossible at worst. If you enjoy a challenge, then here are a few free resources that should be helpful.

Editor’s Note: Collecting specimens is prohibited at Huntley Meadows Park. Further, a permit for Collection of Wildlife for Scientific and/or Educational Purposes is required anywhere in the Commonwealth of Virginia.

Copyright © 2015 Walter Sanford. All rights reserved.

Full Circle

August 21, 2015

A mating pair of Common Green Darners (Anax junius) was spotted at a bioswale near the head-end of the Hike-Bike Trail at Huntley Meadows Park (HMP).

The bioswale was designed to filter the runoff which comes from the parking lot, removing heavy metals, salt, sand, etc. from the runoff before conveyance to Dogue Creek. It is supposed to slowly filter the rain water in 48-72 hours, to clean and purify the water before entering the creek. Source Credit: David M. Lawlor, Natural Resource Manager, HMP.

The pair is in tandem (a form of guarding behavior): the male (upper-right) guides the female (lower-left) to places where she can lay eggs in vegetation (endophytic oviposition).

A mating pair of Common Green Darner dragonflies (Anax junius) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This pair is in tandem as the female lays eggs by the process of oviposition.

05 AUG 2015 | HMP | Common Green Darner (mating pair, in tandem)

Did you notice the odonate exuvia located on the same reed as the Common Green Darners? Although it’s usually impossible to identify an exuvia from a photograph like the one shown above, I consulted the experts of the Northeast Odonata Facebook group.

I can’t identify the exuvia to species, but I’m pretty confident about the family — Libellulidae, a skimmer. Possibly Blue Dasher, but I’m mostly guessing there. Source Credit: Christopher E. Hill, Associate Professor, Department of Biology, Coastal Carolina University.

A mating pair of Common Green Darner dragonflies (Anax junius) spotted at Huntley Meadows Park, Fairfax County, Virginia USA. This pair is in tandem as the female lays eggs by the process of oviposition.

05 AUG 2015 | HMP | Common Green Darner (mating pair, in tandem)

Eggs may hatch after a few days, or embryonic development may take a month or more. In some species, the eggs overwinter and hatch the following spring. Each egg hatches into a very tiny prolarva that looks like a primitive insect form, quite different from the larva that will succeed it. Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 407-409). Princeton University Press. Kindle Edition.

As odonate larvae grow and outgrow their skin, they molt, on average 12 times. The duration of this stage of life can vary from a month to several years, depending upon both species and climate. The last molt, called “emergence,” is the metamorphosis from larva to adult; the “cast skin” that is left behind is an exuvia (pl. exuviae).

The juxtaposition of the exuvia and mating pair in the first photo is a metaphor for the circle of life, come full circle: eggs; prolarvae; larvae; emergence/adult males and females; mating pairs; males guide females to egg-laying sites.

Related Resources:

Copyright © 2015 Walter Sanford. All rights reserved.

Emerging Common Sanddragons

June 29, 2014

Two emerging Common Sanddragon dragonflies (Progomphus obscurus) were spotted on 15 June 2014 during the “Advanced Dragonfly Studies” adult class and field trip to the Patuxent Research Refuge. The field trip was led by Richard Orr, renowned expert on odonates of the mid-Atlantic region, and Stephanie Mason, Senior Naturalist, Audubon Naturalist Society.

emerge: to leave water and undergo metamorphosis into an adult; emergence is thus both from water and from exuvia Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 11593-11594). Princeton University Press. Kindle Edition.

The first two photos show a sanddragon emerging from its exuvia (plural exuviae), also known as a “cast skin.” Notice that its wings have not started expanding.

Common Sanddragon dragonfly (emerging, teneral, exuvia)

Common Sanddragon dragonfly (teneral, exuvia)

The wings, folded like accordions, then begin to fill from the base with fluid transferred from the body and fairly soon reach full length. The fluid is then pumped back into the abdomen, and it expands. Finally, the wings open up, and very soon the teneral adult flies away. Source Credit: Paulson, Dennis (2011-12-19). Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Locations 466-468). Princeton University Press. Kindle Edition.

The last photo shows a teneral adult (upper right) and its exuvia (lower left). Since it takes approximately 30 minutes for dragonfly wings to expand, we can infer this sanddragon emerged before the other one.

Common Sanddragon dragonfly (teneral, exuvia)

Copyright © 2014 Walter Sanford. All rights reserved.


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