There are two (2) genera and five (5) species in Family Macromiidae (Cruisers) that can be found in the Commonwealth of Virginia.
Stream Cruiser (Didymops transversa). MAR 26 – SEP 11.
Allegheny River Cruiser (Macromia alleghaniensis). JUN 4 – AUG 27.
Swift River Cruiser (Macromia illinoiensis) MAY 08 – OCT 10. [This species includes two subspecies: Macromia illonoiensis illinoiensis; and Macromia illinoiensis georgina.]
Mountain River Cruiser (Macromia margarita). MAY 25 – JUN 15.
Royal River Cruiser (Macromia taeniolata). MAY 15 – OCT 10.
Source Credits: A Checklist of North American Odonata
Including English Name, Etymology, Type Locality, and Distribution, by Dennis R. Paulson and Sidney W. Dunkle. Adult flight periods excerpted from “CHECKLIST OF THE DRAGONFLIES AND DAMSELFLIES OF VIRGINIA, April 2017 and April 2020 updates” by Dr. Steve Roble, Staff Zoologist at the Virginia Department of Conservation and Recreation, Division of Natural Heritage.
General Characteristics for Cruisers
All cruisers have a single stripe on the lateral sides of their thorax. All cruisers have spots on top of their frons with the notable exception of Royal River Cruiser (Macromia taeniolata), a key field mark for that species.
Genus Didymops
Stream Cruiser
Stream Cruiser (Didymops transversa) is so distinctive in its appearance that no other species of dragonfly looks similar.
The following composite image shows two (2) female terminal appendages in the background photo; three (3) male appendages are shown in the inset photo.
Genus Macromia
In contrast with genus Didymops, the four species of genus Macromia look similar and can be difficult if not impossible to identify with certainty in the field (especially females of some species).
Accordingly, this identification guide will focus on genus Macromia. Our advice (say it over and over like a mantra): Shoot first (photos, that is) and ask questions later. At a minimum, we recommend photos that show both a dorsal view and lateral view. The more the better! All of that being said, be sure to get at least one “record shot” — get a shot, any shot, and refine the shot as the subject allows.
Photo-illustrated guides for each species in genus Macromia are divided into two sections: one part for males; another part for females. The following field marks can be used to differentiate male versus female dragonflies.
Male: hamules (secondary genitalia located underneath abdominal segments two and three (S2-3); three (3) terminal appendages including two (2) cerci and one (1) epiproct; and “indented” hind wings.
Female: thicker abdomen, no hamules; two (2) cerci; and rounded hind wings.
A three-step process can be used to determine the identity of species in genus Macromia.
- Examine the anterior side of the thorax for the presence or absence of prominent frontal stripes, sometimes referred to as antehumeral stripes. This is a key field mark.
- Examine the pattern of abdominal bands and spots. Bands on abdominal segments two and seven (S2 and S7) are key field marks. They can appear to be complete or broken dorsally, complete or broken laterally, or can encircle the entire abdominal segment.
- Examine the pattern of wing venation, as necessary, specifically the forewing triangle.
Females of Allegheny River Cruiser, Swift River Cruiser (especially the “Illinois” subspecies), and Mountain River Cruiser can be extremely difficult to identify.
Females can be very difficult to distinguish. Source Credit: Paulson, Dennis. Dragonflies and Damselflies of the East (Princeton Field Guides) (Kindle Location 7243). Princeton University Press. Kindle Edition.
Where the ranges of the two subspecies of Swift River Cruiser overlap (including the eastern Piedmont and Coastal Plain of Virginia) individuals with intermediate characteristics might be encountered. It will be impossible to assign these individuals to either subspecies. (Donnelly and Tennessen 1994).
Prominent frontal stripes are present in two species of genus Macromia: Royal River Cruiser (Macromia taeniolata); and Swift “Georgia” River Cruiser (Macromia illinoiensis georgina).
Royal River Cruiser
Male field marks: No pale spots on top of frons; prominent frontal stripes; no club.
Female field marks: No pale spots on top of frons; prominent frontal stripes; either small paired spots or no spots at the base of abdominal segment eight (S8).
Swift “Georgia” River Cruiser
Male field marks: Pale yellow spots on top of frons; prominent frontal stripes; prominent club.
Female field marks: Pale yellow spots on top of frons; prominent frontal stripes; prominent yellow crossbar or band at base of abdominal segment eight (S8).
Prominent frontal stripes are absent in three species of genus Macromia: Allegheny River Cruiser (Macromia alleghaniensis); Swift “Illinois” River Cruiser (Macromia illonoiensis illinoiensis); and Mountain River Cruiser (Macromia margarita).
Allegheny River Cruiser
Editor’s Note: Frontal stripes are present in many individuals, but they are generally short and less prominent.
Male field marks: Band on abdominal segment two (S2) slightly broken dorsally, complete laterally; band on abdominal segment seven (S7) completely encircles the abdomen; mesotibial keel length <20%. [See Michael Moore’s excellent annotated images for good illustrations of mesotibial keels.]
Female field marks: Band on abdominal segment two (S2) broken dorsally, complete laterally; band on abdominal segment seven (S7) broken laterally.
Swift “Illinois” River Cruiser
Male field marks: Band on abdominal segment two (S2) narrow and broken both dorsally and laterally; band on abdominal segment seven (S7) incomplete laterally; generally little or no yellow spots on middle abdominal segments; mesotibial keel length 25-50%.
Editor’s Note: This is the only species of genus Macromia with black auricles.
Female field marks: Band on abdominal segment two (S2) broken dorsally and laterally; band on abdominal segment seven (S7) broken laterally; spots on dorsum of abdomen generally smaller and more triangular than those of Mountain River Cruiser.
Some females might not be identifiable without in-hand examination of the subgenital plate, tibia length, and wing venation (refer to the section entitled “Wing Venation” toward the end of this guide).
Mountain River Cruiser
Editor’s Note: Yellow stripe on the face is brighter with a more narrow brown border.
Male field marks: Band on abdominal segment two (S2) broken dorsally, complete laterally; band on abdominal segment seven (S7) incomplete laterally; mesotibial keel length >50%.
Female field marks: Band on abdominal segment two (S2) broken dorsally and laterally; band on abdominal segment seven (S7) broken laterally; spots on dorsum of abdomen fairly large and squarish.
Wing venation
Wing venation can be used sometimes in conjunction with other characteristics to help distinguish some species of Macromia (river cruisers). However, there is variability within species. In addition, some individuals may exhibit different venation in each wing. Females generally have more crossveins than males. Therefore, one must not rely upon wing venation solely to make a positive identification. The information given here was derived from several scientific sources and represents the most commonly observed venation of both sexes within a species.
Mountain River Cruiser: Forewing triangle usually two-celled and subtriangle usually bordered by three cells; subtriangle one- or two-celled.
Allegheny River Cruiser: Forewing triangle usually one-celled and subtriangle usually bordered by two cells; subtriangle usually one-celled.
Mountain River Cruiser: Forewing triangle 2 celled (90%) and subtriangle bordered by 3 cells (75%); subtriangle 2 celled (55%).
Allegheny River Cruiser: Forewing triangle 1 celled (100%) and subtriangle bordered by 2 cells (100%); subtriangle 1 celled (90%).
Swift “Illinois” River Cruiser: Forewing triangle 1 celled (90%) and subtriangle bordered by 2 cells (70%); subtriangle 1 celled (100%).
Swift “Georgia” River Cruiser: Forewing triangle 2 celled (75%) and subtriangle bordered 2 cells (65%); subtriangle 1 celled (75%).
Royal River Cruiser: Forewing triangle 2 celled (75%) and subtriangle bordered by 3 cells (90%); subtriangle 2 celled (90%).
Editor’s Note: Percentage (%) refers to the percentage of wings showing the venation patterns, among study specimens. (Williamson 1909, and Westfall 1947).
Related Resources
- Williamson, Edward Bruce. 1909. “The North American dragonflies (Odonata) of the genus Macromia.” Proceedings of the United States National Museum. 37 (1710):369–398, 7 figs., 2 pls.. https://doi.org/10.5479/si.00963801.37-1710.369
- Westfall, M. J. “A NEW MACROMIA FROM NORTH CAROLINA.” Journal of the Elisha Mitchell Scientific Society, vol. 63, no. 1, 1947, pp. 32–36. JSTOR, http://www.jstor.org/stable/24334074.
- Donnelly, T. & Tennessen, Kenneth. (1994). Macromia illinoiensis and georgina: a study of their variation and apparent subspecific relationship (Odonata: Corduliidae). Bulletin of American Odonatology. 2. 27. [Editor’s Note: Refer to p. 51 for a map of the eastern half of the United States that shows the ranges for the two subspecies of Swift River Cruiser.]
- PDF version of this guide. [Tech Tip: You must sign in to Facebook in order to download the file.]
Credits
Thanks to Larry Lynch and Joseph Girgente for permission to use their excellent photographs in this guide.
Also sincere thanks to my good friend Mike Boatwright, without whom it would have been impossible for me to create this guide. Mike is a master at odonate identification based upon key field marks — his descriptors provide the essential framework for the guide. And Mike did most of the heavy lifting by annotating all but two of the images featured in this guide. Excellent work, Mike that I’m honored to be able to share with our fellow odonate enthusiasts.
Copyright © 2022 Walter Sanford. All rights reserved.
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