Ophiogomphus aspersus exuvia

A Brook Snaketail dragonfly (Ophiogomphus aspersusnymph was collected by Bob Perkins on either 10 SEP 2017 or 03 OCT 2017 (the date is uncertain) along the New River in southwestern Virginia. The nymph was reared in captivity until it emerged on 31 OCT 2017 and metamorphosed into an adult female. The following specimen is the exuvia from the nymph. Brook Snaketail is a member of the Family Gomphidae (Clubtails).

A two-step process was used to verify the identity 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 Gomphidae (Clubtails).

  • The specimen has a flat labium that doesn’t cover the face (not mask-like), as shown in Photo No. 1, 4, and 5.
  • Antennae are club-like (not thin and thread-like, as in  Aeshnidae larvae), as shown in Photo No. 1.

No. 1 | Ophiogomphus aspersus | exuvia (face-head)

Step 2. Genus and species

The dichotomous key for Ophiogomphus that appears on p. 262 in Dragonflies of North America, Third Edition by Needham et al. was used to verify the genus and species of the exuvia. The eleventh couplet [11, 11′] is as follows.

11(10). Lateral margins of prementum slightly convergent in distal 1/2 (Fig. 320c); lateral abdominal spines about 1/8 length of lateral margin of corresponding segment; in dorsal view, cerci about 2-1/2 times as long as basal width; dorsal hooks on abdominal segments 3-6 erect (Fig. 322d). [aspersus]

11’. Lateral margins of prementum parallel or slightly divergent in distal 1/2 (Fig. 320K); lateral abdominal spines each about 1/5 length of lateral margin of corresponding segment; in dorsal view, cerci each about twice as long as basal width; dorsal hooks on abdominal segments 3-6 appressed (Fig. 322d). [rupinsulensis]

No. 2 | Ophiogomphus aspersus | exuvia (dorsal)

The word “process,” as in “dorsal abdominal process,” is defined as follows.

An upstanding prominence, usually narrow and rod-like or spine-like. Source Credit: Glossary, Dragonflies of North America.

The dorsal hooks, a.k.a., dorsal abdominal processes, on abdominal segments three through six (S3-S6) are erect. Hey, call them whatever you like, including “erect” — there are raised bumps along most of the mid-dorsal abdomen, some of which are raised more noticeably than others, as shown in Photo No. 3.

No. 3 | Ophiogomphus aspersus | exuvia (dorsal-lateral)

The next two annotated images show ventral views of the exuvia.

No. 4 | Ophiogomphus aspersus | exuvia (ventral)

The flat labium doesn’t cover the face and the lateral margins of the prementum are slightly convergent in the distal half, as shown in Photo No. 5.

No. 5 | Ophiogomphus aspersus | exuvia (prementum)

Lateral spines are present on abdominal segments seven through nine (S7-S9) only. Did I measure the length of the lateral abdominal spines to see whether they are about one-eighth (1/8) the length of the lateral margin of the corresponding segment? In a word, no — the length looks about right to my unaided eye.

The cerci are about two-and-a-half (2-1/2) times as long as their basal width. Again, the length looks about right to my unaided eye.

No. 6 | Ophiogomphus aspersus | exuvia (anal pyramid)

The rudimentary ovipositor shown in Photo No. 4 and 7 indicates this individual is a female.

No. 7 | Ophiogomphus aspersus | exuvia (rudimentary ovipositor)

After emergence

The next photograph shows the Brook Snaketail dragonfly after emergence from one of Bob Perkins‘ holding tanks. Ophiogomphus aspersus is 44-49 mm in total length (Paulson, 2011).

Image used with permission from Bob Perkins.

This individual is a female, as indicated by its rounded hind wings and terminal appendages.

Image used with permission from Bob Perkins.

The last close-up photo shows a ventral view of the subgenital plate.

Image used with permission from Bob Perkins.

Tech Tips

The following equipment was used to shoot Photo No. 2-4: Canon EOS 5D Mark II digital camera, in manual mode; Kenko 20mm macro automatic extension tubeCanon EF100mm f/2.8L Macro lens (set for manual focus); Canon MT-26EX-RT Macro Twin Lite set for “Master” mode, and Canon 580 EX- and Canon 580EX II Speedlites set for “Slave” mode. Photo No. 1 and 5-7: Canon MP-E 65mm Macro lens (manual focus only, set for 2x magnification) plus the multiple-flash setup.

Adobe Photoshop CC 2017 was used to annotate selected images.

Bob Perkins’ photos were shot using a Canon EOS Rebel T3i camera body and Canon EF-S 60mm macro lens.

Copyright © 2018 Walter Sanford. All rights reserved.

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