Epitheca cynosura exuvia

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.

No. 1 | Common Baskettail (Epitheca cynosura) | exuvia (face-head)

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

No. 2 | Common Baskettail (Epitheca cynosura) | exuvia (dorsal)

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).

No. 3 | Common Baskettail (Epitheca cynosura) | exuvia (face-head)

(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.

No. 5 | Common Baskettail (Epitheca cynosura) | exuvia (lateral)

(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.

No. 6 | Common Baskettail (Epitheca cynosura) | exuvia (face-head)

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.

• 1 Dorsal hooks present and well developed on some of the abdominal segments. [See Photo No. 4.] 2
• 2 Lateral spines on segment 8. [See Photo No. 7.] 3
• 3 Crenulations of labial palpi much shallower than a semicircle; … [See Photo No. 3.] 4
• 4 Lateral spines on segment 9 more than three times as long as those on segment 8, being at least as long as the mid-dorsal length of segment 9 and usually much longer. [See Photo No. 7.] = Epitheca (includes subgenera Epicordulia and Tetragoneuria)

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

• 1 Lateral spines of segment 9 pointing directly backward, their axes parallel. [See Photo No. 7.] 2
• 2 Lateral spines of segment 9 long, … [See Photo No. 7.] 4
• 4 Length of grown nymph about 22 mm. 5
• 5 Lateral spine of segment 9 about as long as mid-dorsal length of [S]9. [See Photo No. 7.] [premental setae not more than 10] = cynosura

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.

No. 8 | Common Baskettail (Epitheca cynosura) | exuvia (ventral)

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

Related Resources

• Vimeo video: Identifying dragonfly larva to family (8:06)
• Anatomy of a Dragonfly Larva, annotated illustration courtesy Jay Smith
• Identification Keys to Northeastern Anisoptera Larvae, compiled by Ken Soltesz: Alternate Key to the Genera of the Family Corduliidae, p. 29; Key to the species of the genus (subgenus) Tetragoneuria, p. 32.
• Odonate Exuviae – a hyperlinked list of identification guides to many species of odonate exuviae from seven families of dragonflies and three families of damselflies.

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!

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.

Copyright © 2017 Walter Sanford. All rights reserved.

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Tags: cerci, Common Baskettail dragonfly, crenulations, dorsal hooks, epiproct, Epitheca cynosura, exuvia, exuviae, Family Corduliidae (Emeralds), female, gear talk, hamules, labium, lateral spines, Occoquan Bay National Wildlife Refuge, Painted Turtle Pond, paraprocts, postmentum, prementum, teneral