4m. S10 With/Without Pale Dorsal Markings (Males Only)
|Left to right: typical male Shadow Darner with black S10|
male Paddle-tailed Darner with blue on S10; atypical
male Shadow Darner with blue on S10.
I have some male Shadow Darner specimens with small, very obscure pale areas on S10 which may not even be visible in the field. However, I have photos of one exceptionally colorful (more blue than normal) individual which had obvious pale markings on S10, although they were less well-defined than they are on Paddle-tailed. If it wasn’t for that individual, I might have ranked this character a little bit higher in usefulness. On the other hand I have yet to see the opposite variation (lack of, or very small and obscure spots) on male Paddle-tailed Darners, although it’s not impossible. I suppose the rule of thumb here is that if S10 clearly lacks any pale markings, Shadow Darner is a safe bet; the presence of obvious, sharply-defined pale markings very likely indicates Paddle-tailed, but consider the possibility of odd-ball individuals. Again, I remind you to not rely on any single character if possible.
|Female Shadow Darner on left; female|
Paddle-tailed on right. S9, S10, and
bases of broken cerci. On both, note
the small pale areas on the posterior
edge of S10 where the cerci attach.
4f. Shape of Dorsal Abdominal Spots (Females Only)
|Female Shadow Darner on left; female|
Paddle-tailed on right. Middle abdominal
(part of S3 to S7) segments.
On female Shadow Darners, the posterior spots are usually narrow bars with a more-or-less flat (can be slightly convex or slightly concave) anterior edge; the middle spots are vary narrow and only slightly triangular with the inner ends just a little wider than the outer. If they are more clearly triangular, the inner side is less than half the the length of the anterior side.
On female Paddle-tailed Darners, the posterior posts are more oval with a clearly rounded anterior edge (there may be small concave “divets” along that edge); the middle spots are more obviously triangular with the inner edge more than half the length of the anterior edge.
5m. Epiproct Color (Males Only)
I started noticing in my photos that the epiproct (the lower abdominal appendage) on male Shadow Darners, when viewed dorsally, is mostly very pale off-white with a black border. The epiproct on most male Paddle-tailed Darners is all dark (medium brown in the middle if you get a close look), however there seems to be some regional variation in this. You can see the differences in images in section 4m above—it’s pretty obvious when you compare the two Shadow Darners (left and right) with the Paddle-tailed (middle). The epiproct is the shorter appendage between the cerci.
This difference appears to hold up pretty well over most of the Northwest, however I have some specimens of Paddle-tailed Darner from the very arid Alvord Basin in southeast Oregon (part of the Great Basin) which have pale epiprocts very similar to Shadow Darners. I’m going to keep an eye on this character, but it seems to be useful in the more humid, cooler parts of the region, at least.
5f. Presence/Absence of Cerci (Females Only—NOT Reliable)
|End of abdomen of Shadow Darner on|
the left; Paddle-tailed on the right.
I can’t help wondering if female Shadows remove their cerci intentionally as some kind of signal—that they are mature enough to copulate, or that they have already copulated. I don’t know, but I can’t imagine why else they would lose their cerci so much more often than other female darners. A couple of times I caught a female Shadow Darner and, as soon as I pulled her out of the net, the end of her abdomen curled toward the mandibles and “snip, snip”—both cerci fall away. In those cases it was certainly self-inflicted, and the fact that both cerci were bitten off—not just one of them, suggests to me that it wasn’t an “accidental”, random event. We may never know for sure, however.
6m. Shape of Anterior Thoracic Stripes (Males Only)
|Left to right: male Shadow Darner with continually widening anterior thoracic|
stripes; male Paddle-tailed Darner with constricted stripes; male Paddle-tailed
Darner with broken stripes.
There is some overlap in this character: occasional male Paddle-tailed Darners have anterior thoracic stripes which appear parallel-sided before the terminal expansion, and some male Shadow Darners have a very slight constriction before the terminal expansion. For now it appears that this character is useful if it is either wedge-shaped or obviously constricted (or broken), and anything in-between is not useful. As always, don’t rely on any single character whenever possible.
7m. S2 Mid-Dorsal Stripe (Males Only)
|The dorsal surface of S2. Two male Shadow Darners on the left; three Paddle-tailed on the right.|
Something I just noticed while looking at these is that Paddle-tailed Darner has a wide black posterior margin on S2, while Shadow Darner has an extra thin blue line within the black margin. That extra blue line is not always well-defined, but it is present on all of the male Shadow Darners that I have photographed. I also see some differences in the adjacent areas of S3—the extent of blue on the sides and whether they connect across the anterior end of the segment, although that is obviously variable. I’ll look into those some more too.
Over time, I’m sure, some of these characters may prove to be too variable to be very useful, while other potential field marks will come to light. It’s always interesting to see how geographic variation plays a role too—as it appears to do so with male Paddle-tailed Darner epiproct color.
As always, I appreciate feedback, especially if your observations differ from mine.