Macromia illinoiensis exuvia

Post update: Macromiidae exuvia

When this blog post was published on 19 April 2016, I was a novice at identifying odonate exuviae and I was just starting to get serious about studio macro photography. At the time, I was satisfied to be able to identify the dragonfly exuvia as a member of the Family Macromiidae (Cruisers).

What’s new?

I’ve learned a lot since then, including the identity of the specimen to the genus/species level. This is a Swift River Cruiser dragonfly (Macromia illinoiensis) exuvia that was collected along the Potomac River in Fairfax County, Virginia USA.

The first annotated image shows several characters that were used to identify the exuvia to the family level, including a mask-like labium featuring spork-like crenulations and a horn between its pointy eyes.

Swift River Cruiser (Macromia illinoiensis) | exuvia (face-head)

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

The following dorsal view of the exuvia provides enough clues to identify the specimen to the genus/species level.

Swift River Cruiser (Macromia illinoiensis) | exuvia (dorsal)

The lateral spines of abdominal segment nine (S9) do not reach the tips of the inferior appendages (paraprocts), and if you look closely at the full-size version of the preceding photo then you should see a small mid-dorsal hook on abdominal segment 10 (S10). These characters indicate the genus is Macromia.

Notice the lateral spines of abdominal segments eight and nine (S8-9) are “directed straight to rearward,” indicating the species is illinoiensis.

Where it all began.

The last photo shows a teneral male Swift River Cruiser dragonfly clinging to the exuvia from which it emerged — the same exuvia featured in this post! Matt Ryan collected the exuvia after the adult dragonfly flew away from its perch. When Matt gave the exuvia to me several years later, he was unable to remember where it was collected. As soon as I was able to identify the exuvia to the genus/species level, I remembered seeing the following photo posted in one of Matt’s spottings on Project Noah.

Photo used with permission from Matthew J. Ryan.

With a little detective work, I was able to solve the mystery of the specific identity of the exuvia as well as when and where it was collected. Like I said, I’ve learned a lot since I published the first blog post related to this specimen!

Editor’s Notes: A funny thing happened on the way to the forum. I rediscovered the “Key to the Genera of the Family Macromiidae” (p. 27, shown above) while paging through the document Identification Keys to Northeastern Anisoptera Larvae in search of the “Key to the Genera of the Family Corduliidae” (page 28). One look at the line drawing at the bottom of p. 27 and I knew the specific identity of the cruiser exuvia.

I need to refresh this blog post with more annotated images of the Macromia illinoiensis exuvia, including one that clearly shows the mid-dorsal hook on S10, but I was so eager to update the old post that I couldn’t wait to shoot and post-process the new images.

Related Resources

Copyright © 2017 Walter Sanford. All rights reserved.

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