There are quite a few blue dragonflies where I live, so I can’t simply rely on color to tell them apart. Fortunately, it is very easy to identify a male Spangled Skimmer (Libellula cyanea), because it has a white spot beside a black spot on the outer leading edge of each wing—as far as I know, no other dragonfly in our area has multi-colored stigmata, the technical name for those spots.
The stigmata are not there for decoration, but serve an important role in the flight of dragonflies. I do not really understand the physics of flight, but have read that the stigmata are heavier than the adjoining cells and help to stabilize the vibrations of the wings.
I spotted these two mature male Spangled Skimmers during recent trips to Occoquan Regional Park. Earlier this year I saw some immature male Spangled Skimmers at the same location that were brown and yellow in coloration, just like the females of the species. (See my posting from 30 May 2022 entitled Spangled Skimmer dragonflies to see photos of an immature male and a female of this species.) Although the color of the males changes completely as they mature, the distinctive stigmata are present even when they are young.
© Michael Q. Powell. All rights reserved.