Epitheca princeps exuvia

The following Prince Baskettail dragonfly (Epitheca princeps) exuvia, on temporary loan from a friend, had been identified before I borrowed the specimen. A two-step process was used to verify the genus and species of the exuvia.

1. Determine the family.
2. Determine the genus and species.

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. 4.]: 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. 1 | Prince Baskettail (Epitheca princeps) | exuvia (face-head)

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

Step 2. Genus and species

Characters from two dichotomous keys were used to identify the genus and species for the exuvia. Although palpal/mental setae were not examined, all other characters match Epitheca princeps.

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

Dichotomous Key 1

Identification Keys to Northeastern Anisoptera Larvae, compiled by Ken Soltesz.

Key to the Families of Anisoptera, page 5.

• 6 Lateral caudal appendages (cerci) generally more than half as long as inferior appendages (paraprocts) [fig. 12] [See Photo No. 4.]; lateral spines of segment 9 longer than its mid-dorsal length [fig. 13] [See Photo No. 4.]; mid-dorsal hooks on abdomen often cultriform [fig 14] [See Photo No. 3.] Corduliidae

Key to the Genera of the Family Corduliidae, page 28.

• 1 Pair of small tubercles on top of head [See Photo No. 1.]; lateral lobe of labium with 4 or 5 setae… 2
• 2 Lateral spines of abdominal segment 8, if divergent at all, much weaker than those of 9; small setae on middle lobe of mentum numerous. Epicordulia (One species, Epicordulia princeps) [Editor’s Note: Epicordulia was previously considered to be a subgenera of Epitheca.]

Dichotomous Key 2

Corduliidae Selys – Emeralds, Odonata Nymphs of Michigan, by Ethan Bright and Mark F. O’Brien, UMMZ-Insect Division.

• 1b. Mid-dorsal hooks present, well-developed on some abdominal segments (picture) [See Photo No. 3.] – 4
• 4b. With lateral spines on Ab8 [See Photo No. 4.] – 5
• 5b. Crenulations on distal margin shallower than semicircle (picture) [See Photo No. 1.]; lateral spines on Ab9 equal or longer than those on Ab8, those on Ab8 not divergent (fig) [See Photo No. 4.] – 6
• 6a(5b). Lateral spines on Ab9 at least 2.0x as long as those on Ab8, at least equal to mid-dorsal length of Ab9 [See Photo No. 4.] – Epitheca

Epitheca Burmeister, 1839 (Corduliidae) – Baskettails

• 1a. Distal half of dorsal surface of prementum heavily setose; palpal setae usually 4, rarely 5(Fig. 2) – Subgenus Epicordulia, E. princeps

More annotated images

No. 2 | Prince Baskettail (Epitheca princeps) | exuvia (dorsal)

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

“Mid-dorsal hooks present, well-developed on some abdominal segments.”

No. 3 | Prince Baskettail (Epitheca princeps) | exuvia (dorso-lateral)

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

“With lateral spines on Ab8 [S8].” “Lateral spines on Ab9 [S9] at least 2.0x as long as those on Ab8 [S8], at least equal to mid-dorsal length of Ab9 [S9].” The cerci are at least half as long as the paraprocts.

No. 4 | Prince Baskettail (Epitheca princeps) | exuvia (anal pyramid)

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

Photo No. 5 shows a wider view of the ventral side of the specimen.

No. 5 | Prince Baskettail (Epitheca princeps) | exuvia (ventral)

Photo No. 6 shows a zoomed-in view of the prementum.

No. 6 | Prince Baskettail (Epitheca princeps) | exuvia (prementum)

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

Photo No. 7 shows another view of the prementum.

No. 7 | Prince Baskettail (Epitheca princeps) | exuvia (prementum)

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: Key to the Families of Anisoptera, page 5; Key to the Genera of the Family Corduliidae, page 28.
• Odonata Nymphs of Michigan, by Ethan Bright and Mark F. O’Brien, UMMZ-Insect Division: Corduliidae Selys – Emeralds; Epitheca Burmeister, 1839 (Corduliidae) – Baskettails.
• Odonate Exuviae – a hyperlinked list of identification guides to many species of odonate exuviae from seven families of dragonflies and three families of damselflies.

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 and a Raynox DCR-250 close-up filter; Canon 580EX II external flash, off-camera, in manual mode; Canon 580EX external flash, off-camera, in manual mode; and a Yongnuo YN-622C-TX E-TTL II Wireless Flash Controller for Canon plus a two-pack of Yongnuo YN-622C II E-TTL Wireless Flash Transceivers for Canon.

A Canon Extender EF 1.4x II was used for more magnification in Photo No. 4, 6, 7 and 9. Adding the tele-extender results in a 1 f/stop loss of light; additional backlight was added to the scene using a Nissin i40 external flash unit (off-camera, in SF mode).

Adobe Photoshop CC 2017 was used to annotate selected images.

Photo No. 8 and 9 show early work to get a good shot of the face-head, before Photo No. 1 emerged as the clear winner. I prefer Photo No. 1 because it provides the best view of the face-head, has the best composition and exposure, plus I like the way the exuvia seems to be floating in mid-air.

No. 8 | Prince Baskettail (Epitheca princeps) | exuvia (face-head)

No. 9 | Prince Baskettail (Epitheca princeps) | exuvia (face-head)

Although I have never seen a perching adult Prince Baskettail dragonfly, I was fortunate to shoot the following photo of a male in flight, featured in the blog post Changing of the guard.

No. 10 | 14 JUN 2016 | JMAWR | Prince Baskettail (male, in flight)

Copyright © 2017 Walter Sanford. All rights reserved.

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Tags: anal pyramid, cerci, crenulations, dorsal hooks, epiproct, Epitheca princeps, exuvia, Family Corduliidae (Emeralds), gear talk, labium, lateral spines, paraprocts, prementum, Prince Baskettail dragonfly