A dragonfly exuvia from the Family Aeshnidae (Darners) was collected on 21 June 2016 at Hidden Pond, Meadowood Recreation Area, Fairfax County, Virginia USA. This specimen is an exuvia from a Common Green Darner dragonfly (Anax junius).
A two-step process was used to identify the genus and species of the specimen.
- Determine the family.
- 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 I used to identify the exuvia as a member of the Family Aeshnidae (Darners).
- The specimen has a flat labium that doesn’t cover the face (not mask-like), as shown in Photo No. 1-4.
- Antennae are thin and thread-like (not club-like, as in Gomphidae larvae), as shown in Photo No. 4.
- Eyes are large relative to the size of the head, as shown in Photo No. 5.
Step 2. Genus and species
As shown in Photo No. 1, lateral spines along abdominal segments seven, eight, and nine (S7-9) indicate the genus is Anax.
(See a full-size version of the original photo, without annotation.)
At this point, you know the species could be either junius (Common Green Darner dragonfly) or longipes (Comet Darner dragonfly). The species is determined by the shape of the palpal lobes (see Photo No. 3) and the length of the specimen (see Photo No. 2).
(See a full-size version of the original photo, without annotation.)
The labium, also known as the mentum, is 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 specimen is ~4.7 cm (~1.9 in) in length, not counting the bend in the body.
(See a full-size version of the original photo, without annotation.)
The rounded shape of the palpal lobes (see Photo No. 3, above) plus the length of the specimen (see Photo No. 2) indicate the species is junius. Anax junius is one of the more common species of Aeshnidae found in Northern Virginia.
Notice the antennae are thin and thread-like, as shown in the preceding photo. If you are an aquatic animal, this is a face you don’t want to see up-close and personally!
The eyes are large relative to the size of the head.
References
dichotomous key: a key for the identification of organisms based on a series of choices between alternative characters. Source Credit: Merriam-Webster Dictionary.
In long form, the decision tree is as follows (assuming the convention of labeling the two branches of each dichotomy as “a” and “b”, e.g. 1a, 1b, etc.):
p. 21, Key to the genera of the Family Aeshnidae
1b – Hind angles of head rounded … . (5)
5a – Lateral spines on abdominal segments 7 to 9 only. (6)
6b – Antenna about half as long as this distance [from the base of the antennae to the rear of head]. (Anax)
p. 22, Key to the species of the genus Anax
1a – Lateral lobes of labium tapering to a hooked point; total length about 40 mm. (junius) [Note: The total length of longipes is about 55 mm.]
Related Resource: 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); 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 Raynox DCR-250 close-up filter was used for Photo No. 3-5.
Adobe Photoshop CC 2017 was used to annotate selected images.
The first test shot for this exuvia was photographed using my Canon EF100mm f/2.8L Macro lens plus a Kenko 20mm macro automatic extension tube. As you can see in the following photo, the subject barely fit within the frame. Although the composition isn’t ideal, the resulting photo is dramatic nonetheless! The 20mm extension tube wasn’t used for the rest of the photo set.
The following photograph of the exuvia was taken in-situ along the shoreline of Hidden Pond using a Panasonic Lumix DMC-FZ150 superzoom bridge camera and Canon 580EX Speedlite, my go-to kit for photowalking.
Copyright © 2017 Walter Sanford. All rights reserved.
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