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Excerpts from Jim Conrad's
Naturalist Newsletter
from the July 27, 2014 Newsletter issued from the Frio Canyon Nature Education Center in the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau; elevation ~1750m (~5750 ft); N29.62°, W99.86°; USA
PLATEAU SPREADWING
A good half mile (800m) from the nearest standing water in the little Dry Frio River an unfamiliar dragonfly perched on a dead juniper snag near the top of our hill. Any dragonfly on a wooded slope so far from water is unusual, plus this one was boldly colored in a way I hadn't seen, so I worked hard to get the picture shown at http://www.backyardnature.net/n/14/140727df.jpg.
With such striking markings -- especially the thorax so brightly yellow on the sides, the dark "shoulder bands" above, and the long hairs on the legs -- in my Dragonflies through Binoculars field guide by Sidney Dunkle it was easy to peg this as the Black-shouldered Spinyleg, Dromogomphus spinosus, a species described as common in eastern North America.
However, as good ol' volunteer identifier Bea in Ontario was good enough to point out, that ID was wrong. The fundamental error was that our hillside species is not a dragonfly, but rather a damselfly, albeit a member of the Spreadwing Family, the Lestidae, who at rest spread their wings like dragonflies, instead of folding them neatly over their backs like decent damselflies. Bea's reckoning is that this is the Plateau Spreadwing, LESTES ALACER. in the US known from Texas, New Mexico and Arizona. Our Plateau Spreadwing is a female -- the male looking quite different -- and one wonders whether Nature has been at work evolving the two unrelated forms to look so similar!
I find very little about this species on the Internet. At least here we can say that in late July in this part of the world females turn up near the tops of very dry hills covered with scrubby junipers and oaks, and at least that's something.
Entry from field notes dated May 7, 2023, atop hill forested with pines and oaks about 1km east of Curva de la Doctorcilla, on unnamed road connecting Hwy120 and El Doctor; limestone bedrock; elevation ±2650m (8700 ft); Eastern Sierra Madre mountains of east-central Querétaro state, MÉXICO, (N20.88°, W99.62°)
PLATEAU SPREADWING FEMALE IN MEXICO
Here at ±2650m (8700 ft) elevation atop a droughty hill with no ponds, streams or lakes I knew about, it was surprising to see the above damselfly land beside me, turning her head this way and that, apparently waiting for prey to fly by. Damselfly larvae, or naiads, are nearly always aquatic, so where was the home water? Later, on Google Maps, a small, dammed lake was noticed in the valley just below the hilltop, to the east.
Within the insect order Odonata, which is home to both dragonflies and damselflies, damselflies constitute the suborder Zygoptera. Within the Zygoptera, there are various damselfly families. With such a smallish, slender damselfly with transparent wings, it's a good bet that you have a member of the Narrow-winged Damselfly Family, the Coanagrionidae. That's the largest and most commonly encountered damselfly family, with more than 1300 species found worldwide, in over 110 genera.
As seen above, the black, white and tan markings on the sides -- lateral stripes on the abdomen -- were good field marks.
Our hilltop individual was a female, relatively less brightly colored than the male. At the right you see that our female's abdomen tip was plain.
*UPDATE: By doing an image search on damselflies found in our part of upland central Mexico, I decided that this was the olive form of the female Rambur's Forktail, Ischnura ramburii, which we've seen before in Texas (first entry above). However, in 2024 when this page's photos were uploaded to iNaturalist, user "yeseniavega," an evolutionary biologist, recognized the Plateau Spreadwing, Lestes alacer. Despite Rambur's Forktail and the Plateau Spreadwing being in different genera, they are astonishingly similar in appearance. Both species occur here in highland central Mexico, though Rambur's Forktail is much less observed, and on iNatualist not yet recorded from the Eastern Sierra Madres occurring in Querétero state, while several observations of Plateau Spreadwing have been registered.
I can see why an evolutionary biologist would be interested in this species, and hope someday to learn why these two fairly unrelated species look so similar. The main difference I can see is that the white upper stripe on the female's back consistently is broader on the Plateau Spreadwing than the Rambur's Forktail.