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.
Both dragonfly exuviae are from the Family Gomphidae (Clubtails), as indicated by a flat labium that doesn’t cover the face as well as club-like antennae. The smaller specimen was identified as an Erpetogomphus designatus exuvia; this post describes the decision tree used to identify the larger specimen.
Refer to Photo No. 2, 3, and 4. Notice that abdominal segment nine (S9) is elongated, strongly suggesting this individual is a member of the genus Stylurus.
The dichotomous key for Stylurus larvae that appears on pp. 310-312 in Dragonflies of North America, Third Edition by Needham et al. was used to identify the species of the exuvia. The ninth couplet [9, 9′] is as follows.
9(7’). Length of abdominal segment 9 at least equal to its basal width; lateral spines of abdominal segment 9 at least 1-1/2 times as long as those of segment 8; dorsal hook of segment 9 often large, in southern specimens overhanging segment 10; each labial palp with 3 teeth in addition to end hook; greatest width of prementum at least 4/5 its length. [plagiatus]
9’. Length of abdominal segment 9 less than its basal width; lateral spines of abdominal segment 9 no more than 1-1/2 times as long as those of segment 8; dorsal hook of segment 9 small, sometimes vestigial; labial palp with 2-3 teeth in addition to end hook; greatest width of prementum no more than 3/4 its length. [10]
Abdominal segment nine (S9) is slightly longer than its basal width, as shown in Photo No. 2. The lateral spines of segment nine (S9) are much longer than segment eight (S8).
Photo No. 3 shows a dorsal view of the distal abdomen. Notice the large dorsal hook of abdominal segment nine (S9) overhangs segment 10 (S10), a key field mark for southern specimens of plagiatus. The dorsal hook couldn’t be seen before the exuvia was cleaned.
The flat labium doesn’t cover the face, as shown in Photo No. 4 and 5.
Photo No. 5 shows a close-up of the prementum. Each labial palp features at least three (3) teeth in addition to the end hook. The greatest width of the prementum is approximately four-fifths (4/5) of its length.
This specimen is confirmed as an exuvia from a Russet-tipped Clubtail dragonfly (Stylurus plagiatus).
The Backstory
Photo No. 6, featured in a recent blog post entitled Getting Started, is focused on abdominal segment nine (S9).
This specimen may need to be cleaned in order to see more clearly some key field marks used for identification.
The specimen was soaked in soapy water for at least 24 hours. A plastic spoon was used to scoop the exuvia from the water bath and transfer it to a dry plastic tray. Then a soft artist’s paintbrush was used to clean the exuvia, with extra attention on abdominal segment nine (S9). Two damselfly exuviae are soaking in the same water bath, shown below. Other useful tools include a magnifying glass and a plastic toothpick.
The odonate exuviae cleaning station at BoG Photo Studio.
The exuvia is pliable after soaking in water for at least 24 hours. After the specimen was cleaned, it was posed and allowed to dry for another day. The handle of a plastic spoon is a good drying rack that makes it easier to pose the legs. The Stylurus plagiatus exuvia is shown in the following photograph. The broken leg resting on the handle of the spoon was attached to the body only by spider web.
Stylurus plagiatus exuvia, posed on the handle of a plastic spoon.
Related Resources
Tech Tips
The following equipment was used to shoot Photo No. 1, 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. 3 and 5: 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.
A Panasonic Lumix DMC-FZ150 superzoom bridge camera was used to take photos of the odonate exuviae cleaning station.
Adobe Photoshop CC 2017 was used to annotate selected images.
Copyright © 2018 Walter Sanford. All rights reserved.
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