Four species of genus Cordulegaster are found in the Commonwealth of Virginia: Brown Spiketail (C. bilineata); Tiger Spiketail (C. erronea); Twin-spotted Spiketail (C. maculata); and Arrowhead Spiketail (C. obliqua).
According to the excellent datasets for the Commonwealth of Virginia by Dr. Steve Roble, Staff Zoologist at the Virginia Department of Conservation and Recreation, Division of Natural Heritage, the adult flight periods for spiketail dragonflies are as follows.
MAR 16 – JUL 10 = Twin-spotted
MAR 28 – AUG 08 = Brown
MAY 11 – JUL 17 = Arrowhead
MAY 28 – AUG 22 = Tiger
As you can see, there’s a lot of overlap between the flight periods for Twin-spotted Spiketail and Brown Spiketail. Also notice the overlap between the flight periods for Arrowhead Spiketail and Tiger Spiketail.
I think we can agree the distinctive arrowhead-shaped yellow markings on the abdomen of Arrowhead Spiketail (shown below) are unmistakeable for any other species of spiketail, including Tiger Spiketail.
In the opinion of the author it’s more likely a dark-colored Brown Spiketail, such as the one shown below, might be misidentified as a Twin-spotted Spiketail.
Differentiating Twin-spotted versus Brown
Twin-spotted and Brown Spiketail dragonflies can be differentiated by looking closely at the yellow markings on abdominal segments one through three (S1-S3).
The pattern of yellow markings on S1-S3 is simpler for Twin-spotted than Brown, as you can see by looking at the full-size versions of these two photos, shown above and below.
Female Twin-spotted versus Brown
Female Twin-spotted Spiketails, such as the one shown below, have a much longer subgenital plate (ovipositor) than female Brown Spiketails.
The subgenital plate for the following female Brown Spiketail is barely visible.
It isn’t a lot easier to see the subgenital plate in a close-up view of the same individual shown above.
Coach’s Corner
Thanks to Mike Boatwright, founder and administrator of the Virginia Odonata Facebook group, for coaching me up on how to differentiate Twin-spotted Spiketail from Brown Spiketail, including both males and females.
Look for yellow markings on the side of abdominal segments one through three (S1-S3): green arrows show the lack of yellow markings on S1-S3 for Twin-spotted; red arrows show yellow markings on the sides of S1-S3 for Brown.
Set 1
Twin-spotted Spiketail | male (dorsal view)
Brown Spiketail | male (dorsal view)
Set 2
Twin-spotted Spiketail | male (dorso-lateral view)
Brown Spiketail | male (dorso-lateral view)
What are the take-aways?
Remember the odonate hunter’s credo: Shoot first (photographs, that is); ask questions later. (Repeat it like a mantra.) Get a shot, any shot; refine the shot gradually.
Please don’t waste precious time in the field! You can study the photos when you return home in order to identify the subject(s) you shot as either Twin-spotted Spiketail or Brown Spiketail.
Copyright © 2022 Walter Sanford. All rights reserved.
walter sanford's photoblog 