Mike Powell

On Saturday I spotted my first Spangled Skimmer dragonflies (Libellula cyanea) of the year at Occoquan Bay National Wildlife Refuge. It is remarkable easy to identify this species, because it is the only dragonfly in our area that has both black and white stigmata.

The stigmata, or pterostigmata, which is the more technical name, are the pigmented hollow structures on the leading edge of dragonfly wings. They are slightly heavier than the adjoining cells and have a significant effect on the aerodynamics of the wing, particularly while gliding, according to an article entitled “Dragonfly wings: tried and tested over millennia!” I confess that I don’t understand aerodynamics at all and look at dragonfly flight as nothing short of miraculous.

You may have noted that all the dragonflies in all three photos look pretty much the same, but the first two are male and the third is a female. Mature males are blue in color, but when they are young, the immature males share the brown and yellow coloration of the females. The easiest way to tell them apart is to look at the tip of the abdomen (the “tail”)—the terminal appendages of the two genders are quite different in appearance.

© Michael Q. Powell. All rights reserved.