Michael Powell collected several odonate exuviae during a photowalk along the Potomac River in Fairfax County, Virginia USA, including two damselflies and two dragonflies. The exact date is uncertain, although Mike thinks the exuviae were collected sometime between 19-23 July 2017.
A two-step process was used to identify the genus and species of one of the two dragonfly exuviae.
- 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 used to identify the exuvia as a member of the Family Gomphidae (Clubtails).
- The specimen has a flat labium that doesn’t cover the face (not mask-like). [See Photo No. 4.]
- Antennae are club-like (not thin and thread-like, as in Aeshnidae). [See Photo No. 1.]
- Eyes not exceptionally large compared to the size of the head (not large, as in Aeshnidae). [See Photo No. 1.]
No. 1 | Eastern Ringtail (Erpetogomphus designatus) | exuvia (face-head)
(See a full-size version of the original photo, without annotation.)
Step 2. Genus and species
The dichotomous key for Erpetogomphus larvae that appears on pp. 156-157 in Dragonflies of North America, Third Edition by Needham et al. was used to identify the genus and species of the exuvia. The first couplet [1, 1′] is as follows.
1. Dorsal hooks well-developed on abdominal segments 2-9 (Fig. 183a) [2]
1’. Dorsal hooks absent or vestigial on abdominal segments 7-9 (Fig. 183c) (usually present on at least some of the more anterior segments [3]
No. 2 | Eastern Ringtail (Erpetogomphus designatus) | exuvia (dorsal)
(See a full-size version of the original photo, without annotation.)
A leap of faith is required to see the small dorsal hooks present on abdominal segments two through nine (S2 – S9), but they are there.
Notice the divergent wing pads. The white filaments that extend from the split in the thorax (as shown above) are breathing tubes, artifacts of the unique respiratory system of dragonfly nymphs.
2(1). Lateral spines present on abdominal segments 6-9 only; femora with long, hair-like setae [designatus] [Eastern Ringtail]
2’. Lateral spines present on abdominal segments 5-9 only; femora without long, hair-like setae [constrictor] [Knob-tipped Ringtail]
No. 3 | Eastern Ringtail (Erpetogomphus designatus) | exuvia (dorsal)
(See a full-size version of the original photo, without annotation.)
The caudal appendages (terminal appendages) are all about the same length, a key field mark for designatus.
Notice the flat labium that doesn’t cover the face, as shown in the following photo.
No. 4 | Eastern Ringtail (Erpetogomphus designatus) | exuvia (ventral)
This specimen is tentatively identified as an exuvia from an Eastern Ringtail dragonfly (Erpetogomphus designatus). The exuvia that Mike Powell collected is similar in appearance to the following excellent photograph of an Erpetogomphus designatus nymph by Steve Krotzer, Haysop Hill Photography.
Image used with permission from Steve Krotzer.
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 Photo No. 2 and 4: Canon EOS 5D Mark II digital camera, in manual mode; Kenko 20mm macro automatic extension tube; Canon EF100mm f/2.8L Macro lens (set for manual focus); and Canon MT-26EX-RT Macro Twin Lite. Photo No. 1 and 3: Canon EOS 5D Mark II digital camera, in manual mode; Canon MP-E 65mm Macro lens (manual focus only, set for 2x magnification); and Canon MT-26EX-RT Macro Twin Lite. A Sunpak LED-160 Video Light (with a white translucent plastic filter) was used for some photos.
Adobe Photoshop CC 2017 was used to annotate selected images.
Copyright © 2018 Walter Sanford. All rights reserved.
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